Double-tap to zoom and pinch to zoom on ImageView in android

Question

I was looking for iphone like tap and pinch zooming with android ImageView. Mike Ortiz have done some excellent work on TouchImageView to detect boundaries. His code can be found here .

This code is missing only one thing, ie, double-tap to zoom. Can anyone help add this feature to Mike Ortiz code?

Answer 1

It's old, but as no answer picked as correct, I would like to share it.

I've tweaked the TouchImageView class in this answer to support double tap for zooming in/out by implementing GestureDetector.OnGestureListener , GestureDetector.OnDoubleTapListener interfaces

import android.content.Context;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.ImageView;

public class TouchImageView extends ImageView implements GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener {

    Matrix matrix;

    // We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;

    // Remember some things for zooming
    PointF last = new PointF();
    PointF start = new PointF();
    float minScale = 1f;
    float maxScale = 3f;
    float[] m;

    int viewWidth, viewHeight;
    static final int CLICK = 3;
    float saveScale = 1f;
    protected float origWidth, origHeight;
    int oldMeasuredWidth, oldMeasuredHeight;

    ScaleGestureDetector mScaleDetector;

    Context context;

    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }

    GestureDetector mGestureDetector;

    private void sharedConstructing(Context context) {
        super.setClickable(true);
        this.context = context;
        mGestureDetector = new GestureDetector(context, this);
        mGestureDetector.setOnDoubleTapListener(this);

        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        matrix = new Matrix();
        m = new float[9];
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);

        setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent event) {
                mScaleDetector.onTouchEvent(event);
                mGestureDetector.onTouchEvent(event);

                PointF curr = new PointF(event.getX(), event.getY());

                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        last.set(curr);
                        start.set(last);
                        mode = DRAG;
                        break;

                    case MotionEvent.ACTION_MOVE:
                        if (mode == DRAG) {
                            float deltaX = curr.x - last.x;
                            float deltaY = curr.y - last.y;
                            float fixTransX = getFixDragTrans(deltaX, viewWidth,
                                    origWidth * saveScale);
                            float fixTransY = getFixDragTrans(deltaY, viewHeight,
                                    origHeight * saveScale);
                            matrix.postTranslate(fixTransX, fixTransY);
                            fixTrans();
                            last.set(curr.x, curr.y);
                        }
                        break;

                    case MotionEvent.ACTION_UP:
                        mode = NONE;
                        int xDiff = (int) Math.abs(curr.x - start.x);
                        int yDiff = (int) Math.abs(curr.y - start.y);
                        if (xDiff < CLICK && yDiff < CLICK)
                            performClick();
                        break;

                    case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        break;
                }

                setImageMatrix(matrix);
                invalidate();
                return true; // indicate event was handled
            }

        });
    }

    public void setMaxZoom(float x) {
        maxScale = x;
    }

    @Override
    public boolean onSingleTapConfirmed(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        // Double tap is detected
        Log.i("MAIN_TAG", "Double tap detected");
        float origScale = saveScale;
        float mScaleFactor;

        if (saveScale == maxScale) {
            saveScale = minScale;
            mScaleFactor = minScale / origScale;
        } else {
            saveScale = maxScale;
            mScaleFactor = maxScale / origScale;
        }

        matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2,
                viewHeight / 2);

        fixTrans();
        return false;
    }

    @Override
    public boolean onDoubleTapEvent(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onDown(MotionEvent e) {
        return false;
    }

    @Override
    public void onShowPress(MotionEvent e) {

    }

    @Override
    public boolean onSingleTapUp(MotionEvent e) {
        return false;
    }

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
        return false;
    }

    @Override
    public void onLongPress(MotionEvent e) {

    }

    @Override
    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
        return false;
    }

    private class ScaleListener extends
            ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScaleBegin(ScaleGestureDetector detector) {
            mode = ZOOM;
            return true;
        }

        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            float mScaleFactor = detector.getScaleFactor();
            float origScale = saveScale;
            saveScale *= mScaleFactor;
            if (saveScale > maxScale) {
                saveScale = maxScale;
                mScaleFactor = maxScale / origScale;
            } else if (saveScale < minScale) {
                saveScale = minScale;
                mScaleFactor = minScale / origScale;
            }

            if (origWidth * saveScale <= viewWidth
                    || origHeight * saveScale <= viewHeight)
                matrix.postScale(mScaleFactor, mScaleFactor, viewWidth / 2,
                        viewHeight / 2);
            else
                matrix.postScale(mScaleFactor, mScaleFactor,
                        detector.getFocusX(), detector.getFocusY());

            fixTrans();
            return true;
        }
    }

    void fixTrans() {
        matrix.getValues(m);
        float transX = m[Matrix.MTRANS_X];
        float transY = m[Matrix.MTRANS_Y];

        float fixTransX = getFixTrans(transX, viewWidth, origWidth * saveScale);
        float fixTransY = getFixTrans(transY, viewHeight, origHeight
                * saveScale);

        if (fixTransX != 0 || fixTransY != 0)
            matrix.postTranslate(fixTransX, fixTransY);
    }

    float getFixTrans(float trans, float viewSize, float contentSize) {
        float minTrans, maxTrans;

        if (contentSize <= viewSize) {
            minTrans = 0;
            maxTrans = viewSize - contentSize;
        } else {
            minTrans = viewSize - contentSize;
            maxTrans = 0;
        }

        if (trans < minTrans)
            return -trans + minTrans;
        if (trans > maxTrans)
            return -trans + maxTrans;
        return 0;
    }

    float getFixDragTrans(float delta, float viewSize, float contentSize) {
        if (contentSize <= viewSize) {
            return 0;
        }
        return delta;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = MeasureSpec.getSize(widthMeasureSpec);
        viewHeight = MeasureSpec.getSize(heightMeasureSpec);

        //
        // Rescales image on rotation
        //
        if (oldMeasuredHeight == viewWidth && oldMeasuredHeight == viewHeight
                || viewWidth == 0 || viewHeight == 0)
            return;
        oldMeasuredHeight = viewHeight;
        oldMeasuredWidth = viewWidth;

        if (saveScale == 1) {
            // Fit to screen.
            float scale;

            Drawable drawable = getDrawable();
            if (drawable == null || drawable.getIntrinsicWidth() == 0
                    || drawable.getIntrinsicHeight() == 0)
                return;
            int bmWidth = drawable.getIntrinsicWidth();
            int bmHeight = drawable.getIntrinsicHeight();

            Log.d("bmSize", "bmWidth: " + bmWidth + " bmHeight : " + bmHeight);

            float scaleX = (float) viewWidth / (float) bmWidth;
            float scaleY = (float) viewHeight / (float) bmHeight;
            scale = Math.min(scaleX, scaleY);
            matrix.setScale(scale, scale);

            // Center the image
            float redundantYSpace = (float) viewHeight
                    - (scale * (float) bmHeight);
            float redundantXSpace = (float) viewWidth
                    - (scale * (float) bmWidth);
            redundantYSpace /= (float) 2;
            redundantXSpace /= (float) 2;

            matrix.postTranslate(redundantXSpace, redundantYSpace);

            origWidth = viewWidth - 2 * redundantXSpace;
            origHeight = viewHeight - 2 * redundantYSpace;
            setImageMatrix(matrix);
        }
        fixTrans();
    }
}

Usage: You can replace your ImageView with TouchImageView in both XML & java

1. For XML

<?xml version="1.0" encoding="utf-8"?>
<com.example.android.myapp.TouchImageView 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/imViewedImage"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clickable="true"
    android:focusable="true" />

2. For Java

TouchImageView imViewedImage = findViewById(R.id.imViewedImage);

Answer 2

Pinch Zoom on ImageView in Android with Orientation handling

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PointF;
import android.os.Handler;
import android.util.AttributeSet;
import android.util.FloatMath;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.GestureDetector.SimpleOnGestureListener;

public class ZoomableImageView extends View {
    private static final String TAG = "ZoomableImageView";       

    private Bitmap imgBitmap = null;

    private int containerWidth;
    private int containerHeight;

    Paint background;   

    //Matrices will be used to move and zoom image
    Matrix matrix = new Matrix();
    Matrix savedMatrix = new Matrix();

    PointF start = new PointF();       

    float currentScale;
    float curX;
    float curY;

    //We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;

    //For animating stuff   
    float targetX;
    float targetY;
    float targetScale;
    float targetScaleX;
    float targetScaleY;
    float scaleChange;
    float targetRatio;
    float transitionalRatio;

    float easing = 0.2f;   
    boolean isAnimating = false;

    float scaleDampingFactor = 0.5f;

    //For pinch and zoom
    float oldDist = 1f;   
    PointF mid = new PointF();

    private Handler mHandler = new Handler();       

    float minScale;
    float maxScale = 8.0f;

    float wpRadius = 25.0f;
    float wpInnerRadius = 20.0f;

    float screenDensity;

    private GestureDetector gestureDetector;

    public static final int DEFAULT_SCALE_FIT_INSIDE = 0;
    public static final int DEFAULT_SCALE_ORIGINAL = 1;

    private int defaultScale;

    public int getDefaultScale() {
        return defaultScale;
    }

    public void setDefaultScale(int defaultScale) {
        this.defaultScale = defaultScale;
    }

    public ZoomableImageView(Context context) {
        super(context);       
        setFocusable(true);
        setFocusableInTouchMode(true);

        screenDensity = context.getResources().getDisplayMetrics().density;

        initPaints();
        gestureDetector = new GestureDetector(new MyGestureDetector());       
    }

    public ZoomableImageView(Context context, AttributeSet attrs) {
        super(context, attrs);

        screenDensity = context.getResources().getDisplayMetrics().density;       
        initPaints();
        gestureDetector = new GestureDetector(new MyGestureDetector());

        defaultScale = ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE;
    }

    private void initPaints() {
        background = new Paint();
    }

    @Override
    protected void onSizeChanged(int width, int height, int oldWidth, int oldHeight) {
        super.onSizeChanged(width, height, oldWidth, oldHeight);

        //Reset the width and height. Will draw bitmap and change
        containerWidth = width;
        containerHeight = height;

        if(imgBitmap != null) {
            int imgHeight = imgBitmap.getHeight();
            int imgWidth = imgBitmap.getWidth();

            float scale;
            int initX = 0;
            int initY = 0;           

            if(defaultScale == ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE) {               
                if(imgWidth > containerWidth) {           
                    scale = (float)containerWidth / imgWidth;           
                    float newHeight = imgHeight * scale;           
                    initY = (containerHeight - (int)newHeight)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(0, initY);
                }
                else {           
                    scale = (float)containerHeight / imgHeight;
                    float newWidth = imgWidth * scale;
                    initX = (containerWidth - (int)newWidth)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = scale;
                minScale = scale;
            }
            else {
                if(imgWidth > containerWidth) {                                   
                    initY = (containerHeight - (int)imgHeight)/2;                   
                    matrix.postTranslate(0, initY);
                }
                else {                               
                    initX = (containerWidth - (int)imgWidth)/2;                   
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = 1.0f;
                minScale = 1.0f;               
            }


            invalidate();           
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {               
        if(imgBitmap != null && canvas != null)
        {                                           
            canvas.drawBitmap(imgBitmap, matrix, background);                                                   
        }
    }

    //Checks and sets the target image x and y co-ordinates if out of bounds
    private void checkImageConstraints() {
        if(imgBitmap == null) {
            return;
        }

        float[] mvals = new float[9];
        matrix.getValues(mvals);

        currentScale = mvals[0];

        if(currentScale < minScale) {                               
            float deltaScale = minScale / currentScale;                   
            float px = containerWidth/2;
            float py = containerHeight/2;           
            matrix.postScale(deltaScale, deltaScale, px, py);
            invalidate();
        }       

        matrix.getValues(mvals);
        currentScale = mvals[0];
        curX = mvals[2];
        curY = mvals[5];

        int rangeLimitX = containerWidth - (int)(imgBitmap.getWidth() * currentScale);
        int rangeLimitY = containerHeight - (int)(imgBitmap.getHeight() * currentScale);


        boolean toMoveX = false;
        boolean toMoveY = false;   

        if(rangeLimitX < 0) {
            if(curX > 0) {
                targetX = 0;
                toMoveX = true;
            }
            else if(curX < rangeLimitX) {
                targetX = rangeLimitX;
                toMoveX = true;
            }
        }
        else {
            targetX = rangeLimitX / 2;
            toMoveX = true;
        }

        if(rangeLimitY < 0) {
            if(curY > 0) {
                targetY = 0;
                toMoveY = true;
            }
            else if(curY < rangeLimitY) {
                targetY = rangeLimitY;
                toMoveY = true;
            }
        }
        else {
            targetY = rangeLimitY / 2;
            toMoveY = true;
        }

        if(toMoveX == true || toMoveY == true) {
            if(toMoveY == false) {
                targetY = curY;
            }
            if(toMoveX == false) {
                targetX = curX;
            }           

            //Disable touch event actions
            isAnimating = true;
            //Initialize timer           
            mHandler.removeCallbacks(mUpdateImagePositionTask);
            mHandler.postDelayed(mUpdateImagePositionTask, 100);
        }
    }       


    @Override
    public boolean onTouchEvent(MotionEvent event) {       
        if(gestureDetector.onTouchEvent(event)) {
            return true;
        }

        if(isAnimating == true) {
            return true;
        }

        //Handle touch events here       
        float[] mvals = new float[9];
        switch(event.getAction() & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            if(isAnimating == false) {
                savedMatrix.set(matrix);
                start.set(event.getX(), event.getY());           
                mode = DRAG;               
            }
        break;

        case MotionEvent.ACTION_POINTER_DOWN:
            oldDist = spacing(event);           
            if(oldDist > 10f) {
                savedMatrix.set(matrix);
                midPoint(mid, event);
                mode = ZOOM;
            }
        break;

        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_POINTER_UP:
            mode = NONE;

            matrix.getValues(mvals);
            curX = mvals[2];
            curY = mvals[5];
            currentScale = mvals[0];

            if(isAnimating == false) {                                       
                checkImageConstraints();
            }
        break;

        case MotionEvent.ACTION_MOVE:           
            if(mode == DRAG && isAnimating == false) {
                matrix.set(savedMatrix);
                float diffX = event.getX() - start.x;
                float diffY = event.getY() - start.y;

                matrix.postTranslate(diffX, diffY);

                matrix.getValues(mvals);
                curX = mvals[2];
                curY = mvals[5];
                currentScale = mvals[0];
            }
            else if(mode == ZOOM && isAnimating == false) {
                float newDist = spacing(event);               
                if(newDist > 10f) {
                    matrix.set(savedMatrix);
                    float scale = newDist / oldDist;                   
                    matrix.getValues(mvals);
                    currentScale = mvals[0];

                    if(currentScale * scale <= minScale) {
                        matrix.postScale(minScale/currentScale, minScale/currentScale, mid.x, mid.y);
                    }                   
                    else if(currentScale * scale >= maxScale) {
                        matrix.postScale(maxScale/currentScale, maxScale/currentScale, mid.x, mid.y);
                    }
                    else {
                        matrix.postScale(scale, scale, mid.x, mid.y);
                    }


                    matrix.getValues(mvals);
                    curX = mvals[2];
                    curY = mvals[5];
                    currentScale = mvals[0];                                       
                }
            }

        break;                               
        }

        //Calculate the transformations and then invalidate
        invalidate();
        return true;
    }

    private float spacing(MotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return FloatMath.sqrt(x * x + y * y);
    }

    private void midPoint(PointF point, MotionEvent event) {
        float x = event.getX(0) + event.getX(1);
        float y = event.getY(0) + event.getY(1);
        point.set(x/2, y/2);
    }

    public void setImageBitmap(Bitmap b) {       
        if(b != null) {
            imgBitmap = b;               

            containerWidth = getWidth();
            containerHeight = getHeight();

            int imgHeight = imgBitmap.getHeight();
            int imgWidth = imgBitmap.getWidth();

            float scale;
            int initX = 0;
            int initY = 0;

            matrix.reset();

            if(defaultScale == ZoomableImageView.DEFAULT_SCALE_FIT_INSIDE) {               
                if(imgWidth > containerWidth) {           
                    scale = (float)containerWidth / imgWidth;           
                    float newHeight = imgHeight * scale;           
                    initY = (containerHeight - (int)newHeight)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(0, initY);
                }
                else {           
                    scale = (float)containerHeight / imgHeight;
                    float newWidth = imgWidth * scale;
                    initX = (containerWidth - (int)newWidth)/2;

                    matrix.setScale(scale, scale);
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = scale;
                minScale = scale;
            }
            else {
                if(imgWidth > containerWidth) {
                    initX = 0;
                    if(imgHeight > containerHeight) {                       
                        initY = 0;
                    }
                    else {                       
                        initY = (containerHeight - (int)imgHeight)/2;
                    }

                    matrix.postTranslate(0, initY);
                }
                else {                               
                    initX = (containerWidth - (int)imgWidth)/2;
                    if(imgHeight > containerHeight) {
                        initY = 0;
                    }
                    else {
                        initY = (containerHeight - (int)imgHeight)/2;
                    }
                    matrix.postTranslate(initX, 0);
                }

                curX = initX;
                curY = initY;

                currentScale = 1.0f;
                minScale = 1.0f;               
            }

            invalidate();           
        }
        else {
            Log.d(TAG, "bitmap is null");
        }
    }

    public Bitmap getPhotoBitmap() {       
        return imgBitmap;
    }


    private Runnable mUpdateImagePositionTask = new Runnable() {
        public void run() {       
            float[] mvals;

            if(Math.abs(targetX - curX) < 5 && Math.abs(targetY - curY) < 5) {
                isAnimating = false;
                mHandler.removeCallbacks(mUpdateImagePositionTask);

                mvals = new float[9];
                matrix.getValues(mvals);

                currentScale = mvals[0];
                curX = mvals[2];
                curY = mvals[5];

                //Set the image parameters and invalidate display
                float diffX = (targetX - curX);
                float diffY = (targetY - curY);

                matrix.postTranslate(diffX, diffY);
            }
            else {
                isAnimating = true;
                mvals = new float[9];
                matrix.getValues(mvals);

                currentScale = mvals[0];
                curX = mvals[2];
                curY = mvals[5];

                //Set the image parameters and invalidate display
                float diffX = (targetX - curX) * 0.3f;
                float diffY = (targetY - curY) * 0.3f;

                matrix.postTranslate(diffX, diffY);               
                mHandler.postDelayed(this, 25);               
            }

            invalidate();           
        }
    };

    private Runnable mUpdateImageScale = new Runnable() {
        public void run() {           
            float transitionalRatio = targetScale / currentScale;           
            float dx;
            if(Math.abs(transitionalRatio - 1) > 0.05) {
                isAnimating = true;               
                if(targetScale > currentScale) {                                       
                    dx = transitionalRatio - 1;
                    scaleChange = 1 + dx * 0.2f;

                    currentScale *= scaleChange;

                    if(currentScale > targetScale) {
                        currentScale = currentScale / scaleChange;
                        scaleChange = 1;
                    }
                }
                else {                                   
                    dx = 1 - transitionalRatio;                   
                    scaleChange = 1 - dx * 0.5f;
                    currentScale *= scaleChange;

                    if(currentScale < targetScale) {
                        currentScale = currentScale / scaleChange;
                        scaleChange = 1;
                    }
                }


                if(scaleChange != 1) {
                    matrix.postScale(scaleChange, scaleChange, targetScaleX, targetScaleY);               
                    mHandler.postDelayed(mUpdateImageScale, 15);
                    invalidate();
                }
                else {
                    isAnimating = false;
                    scaleChange = 1;                   
                    matrix.postScale(targetScale/currentScale, targetScale/currentScale, targetScaleX, targetScaleY);
                    currentScale = targetScale;
                    mHandler.removeCallbacks(mUpdateImageScale);
                    invalidate();
                    checkImageConstraints();
                }               
            }
            else {
                isAnimating = false;
                scaleChange = 1;               
                matrix.postScale(targetScale/currentScale, targetScale/currentScale, targetScaleX, targetScaleY);
                currentScale = targetScale;
                mHandler.removeCallbacks(mUpdateImageScale);
                invalidate();
                checkImageConstraints();
            }                               
        }
    };

   /** Show an event in the LogCat view, for debugging */
   private void dumpEvent(MotionEvent event) {
      String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE", "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
      StringBuilder sb = new StringBuilder();
      int action = event.getAction();
      int actionCode = action & MotionEvent.ACTION_MASK;
      sb.append("event ACTION_").append(names[actionCode]);
      if (actionCode == MotionEvent.ACTION_POINTER_DOWN || actionCode == MotionEvent.ACTION_POINTER_UP) {
         sb.append("(pid ").append(action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
         sb.append(")");
      }
      sb.append("[");

      for (int i = 0; i < event.getPointerCount(); i++) {
         sb.append("#").append(i);
         sb.append("(pid ").append(event.getPointerId(i));
         sb.append(")=").append((int) event.getX(i));
         sb.append(",").append((int) event.getY(i));
         if (i + 1 < event.getPointerCount())
            sb.append(";");
      }
      sb.append("]");
   }

   class MyGestureDetector extends SimpleOnGestureListener {
        @Override
        public boolean onDoubleTap(MotionEvent event) {           
            if(isAnimating == true) {
                return true;
            }

            scaleChange = 1;
            isAnimating = true;
            targetScaleX = event.getX();
            targetScaleY = event.getY();

            if(Math.abs(currentScale - maxScale) > 0.1) {           
                targetScale = maxScale;
            }
            else {
                targetScale = minScale;
            }
            targetRatio = targetScale / currentScale;
            mHandler.removeCallbacks(mUpdateImageScale);
            mHandler.post(mUpdateImageScale);           
            return true;
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            return super.onFling(e1, e2, velocityX, velocityY);
        }

        @Override
        public boolean onDown(MotionEvent e) {
            return false;
        }
    }
}

Answer 3

Here it works with both Pinch to Zoom and Double tap to Zoom:

import android.annotation.TargetApi;
import android.content.Context;
import android.content.res.Configuration;
import android.graphics.*;
import android.graphics.drawable.Drawable;
import android.net.Uri;
import android.os.Build.VERSION;
import android.os.Build.VERSION_CODES;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.widget.OverScroller;
import android.widget.Scroller;
import androidx.appcompat.widget.AppCompatImageView;

public class TouchImageView extends AppCompatImageView {

    private static final String DEBUG = "DEBUG";

    //
    // SuperMin and SuperMax multipliers. Determine how much the image can be
    // zoomed below or above the zoom boundaries, before animating back to the
    // min/max zoom boundary.
    //
    private static final float SUPER_MIN_MULTIPLIER = .75f;
    private static final float SUPER_MAX_MULTIPLIER = 1.25f;

    //
    // Scale of image ranges from minScale to maxScale, where minScale == 1
    // when the image is stretched to fit view.
    //
    private float normalizedScale;

    //
    // Matrix applied to image. MSCALE_X and MSCALE_Y should always be equal.
    // MTRANS_X and MTRANS_Y are the other values used. prevMatrix is the matrix
    // saved prior to the screen rotating.
    //
    private Matrix matrix, prevMatrix;

    private static enum State {NONE, DRAG, ZOOM, FLING, ANIMATE_ZOOM}

    ;
    private State state;

    private float minScale;
    private float maxScale;
    private float superMinScale;
    private float superMaxScale;
    private float[] m;

    private Context context;
    private Fling fling;

    private ScaleType mScaleType;

    private boolean imageRenderedAtLeastOnce;
    private boolean onDrawReady;

    private ZoomVariables delayedZoomVariables;

    //
    // Size of view and previous view size (ie before rotation)
    //
    private int viewWidth, viewHeight, prevViewWidth, prevViewHeight;

    //
    // Size of image when it is stretched to fit view. Before and After rotation.
    //
    private float matchViewWidth, matchViewHeight, prevMatchViewWidth, prevMatchViewHeight;

    private ScaleGestureDetector mScaleDetector;
    private GestureDetector mGestureDetector;
    private GestureDetector.OnDoubleTapListener doubleTapListener = null;
    private OnTouchListener userTouchListener = null;
    private OnTouchImageViewListener touchImageViewListener = null;

    public TouchImageView(Context context) {
        super(context);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        sharedConstructing(context);
    }

    public TouchImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        sharedConstructing(context);
    }

    private void sharedConstructing(Context context) {
        super.setClickable(true);
        this.context = context;
        mScaleDetector = new ScaleGestureDetector(context, new ScaleListener());
        mGestureDetector = new GestureDetector(context, new GestureListener());
        matrix = new Matrix();
        prevMatrix = new Matrix();
        m = new float[9];
        normalizedScale = 1;
        if (mScaleType == null) {
            mScaleType = ScaleType.FIT_CENTER;
        }
        minScale = 1;
        maxScale = 3;
        superMinScale = SUPER_MIN_MULTIPLIER * minScale;
        superMaxScale = SUPER_MAX_MULTIPLIER * maxScale;
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);
        setState(State.NONE);
        onDrawReady = false;
        super.setOnTouchListener(new PrivateOnTouchListener());
    }

    @Override
    public void setOnTouchListener(OnTouchListener l) {
        userTouchListener = l;
    }

    public void setOnTouchImageViewListener(OnTouchImageViewListener l) {
        touchImageViewListener = l;
    }

    public void setOnDoubleTapListener(GestureDetector.OnDoubleTapListener l) {
        doubleTapListener = l;
    }

    @Override
    public void setImageResource(int resId) {
        super.setImageResource(resId);
        savePreviousImageValues();
        fitImageToView();
    }

    @Override
    public void setImageBitmap(Bitmap bm) {
        super.setImageBitmap(bm);
        savePreviousImageValues();
        fitImageToView();
    }

    @Override
    public void setImageDrawable(Drawable drawable) {
        super.setImageDrawable(drawable);
        savePreviousImageValues();
        fitImageToView();
    }

    @Override
    public void setImageURI(Uri uri) {
        super.setImageURI(uri);
        savePreviousImageValues();
        fitImageToView();
    }

    @Override
    public void setScaleType(ScaleType type) {
        if (type == ScaleType.FIT_START || type == ScaleType.FIT_END) {
            throw new UnsupportedOperationException("TouchImageView does not support FIT_START or FIT_END");
        }
        if (type == ScaleType.MATRIX) {
            super.setScaleType(ScaleType.MATRIX);

        } else {
            mScaleType = type;
            if (onDrawReady) {
                //
                // If the image is already rendered, scaleType has been called programmatically
                // and the TouchImageView should be updated with the new scaleType.
                //
                setZoom(this);
            }
        }
    }

    @Override
    public ScaleType getScaleType() {
        return mScaleType;
    }

    /**
     * Returns false if image is in initial, unzoomed state. False, otherwise.
     *
     * @return true if image is zoomed
     */
    public boolean isZoomed() {
        return normalizedScale != 1;
    }

    /**
     * Return a Rect representing the zoomed image.
     *
     * @return rect representing zoomed image
     */
    public RectF getZoomedRect() {
        if (mScaleType == ScaleType.FIT_XY) {
            throw new UnsupportedOperationException("getZoomedRect() not supported with FIT_XY");
        }
        PointF topLeft = transformCoordTouchToBitmap(0, 0, true);
        PointF bottomRight = transformCoordTouchToBitmap(viewWidth, viewHeight, true);

        float w = getDrawable().getIntrinsicWidth();
        float h = getDrawable().getIntrinsicHeight();
        return new RectF(topLeft.x / w, topLeft.y / h, bottomRight.x / w, bottomRight.y / h);
    }

    /**
     * Save the current matrix and view dimensions
     * in the prevMatrix and prevView variables.
     */
    private void savePreviousImageValues() {
        if (matrix != null && viewHeight != 0 && viewWidth != 0) {
            matrix.getValues(m);
            prevMatrix.setValues(m);
            prevMatchViewHeight = matchViewHeight;
            prevMatchViewWidth = matchViewWidth;
            prevViewHeight = viewHeight;
            prevViewWidth = viewWidth;
        }
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Bundle bundle = new Bundle();
        bundle.putParcelable("instanceState", super.onSaveInstanceState());
        bundle.putFloat("saveScale", normalizedScale);
        bundle.putFloat("matchViewHeight", matchViewHeight);
        bundle.putFloat("matchViewWidth", matchViewWidth);
        bundle.putInt("viewWidth", viewWidth);
        bundle.putInt("viewHeight", viewHeight);
        matrix.getValues(m);
        bundle.putFloatArray("matrix", m);
        bundle.putBoolean("imageRendered", imageRenderedAtLeastOnce);
        return bundle;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        if (state instanceof Bundle) {
            Bundle bundle = (Bundle) state;
            normalizedScale = bundle.getFloat("saveScale");
            m = bundle.getFloatArray("matrix");
            prevMatrix.setValues(m);
            prevMatchViewHeight = bundle.getFloat("matchViewHeight");
            prevMatchViewWidth = bundle.getFloat("matchViewWidth");
            prevViewHeight = bundle.getInt("viewHeight");
            prevViewWidth = bundle.getInt("viewWidth");
            imageRenderedAtLeastOnce = bundle.getBoolean("imageRendered");
            super.onRestoreInstanceState(bundle.getParcelable("instanceState"));
            return;
        }

        super.onRestoreInstanceState(state);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        onDrawReady = true;
        imageRenderedAtLeastOnce = true;
        if (delayedZoomVariables != null) {
            setZoom(delayedZoomVariables.scale, delayedZoomVariables.focusX, delayedZoomVariables.focusY, delayedZoomVariables.scaleType);
            delayedZoomVariables = null;
        }
        super.onDraw(canvas);
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        savePreviousImageValues();
    }

    /**
     * Get the max zoom multiplier.
     *
     * @return max zoom multiplier.
     */
    public float getMaxZoom() {
        return maxScale;
    }

    /**
     * Set the max zoom multiplier. Default value: 3.
     *
     * @param max max zoom multiplier.
     */
    public void setMaxZoom(float max) {
        maxScale = max;
        superMaxScale = SUPER_MAX_MULTIPLIER * maxScale;
    }

    /**
     * Get the min zoom multiplier.
     *
     * @return min zoom multiplier.
     */
    public float getMinZoom() {
        return minScale;
    }

    /**
     * Get the current zoom. This is the zoom relative to the initial
     * scale, not the original resource.
     *
     * @return current zoom multiplier.
     */
    public float getCurrentZoom() {
        return normalizedScale;
    }

    /**
     * Set the min zoom multiplier. Default value: 1.
     *
     * @param min min zoom multiplier.
     */
    public void setMinZoom(float min) {
        minScale = min;
        superMinScale = SUPER_MIN_MULTIPLIER * minScale;
    }

    /**
     * Reset zoom and translation to initial state.
     */
    public void resetZoom() {
        normalizedScale = 1;
        fitImageToView();
    }

    /**
     * Set zoom to the specified scale. Image will be centered by default.
     *
     * @param scale
     */
    public void setZoom(float scale) {
        setZoom(scale, 0.5f, 0.5f);
    }

    /**
     * Set zoom to the specified scale. Image will be centered around the point
     * (focusX, focusY). These floats range from 0 to 1 and denote the focus point
     * as a fraction from the left and top of the view. For example, the top left
     * corner of the image would be (0, 0). And the bottom right corner would be (1, 1).
     *
     * @param scale
     * @param focusX
     * @param focusY
     */
    public void setZoom(float scale, float focusX, float focusY) {
        setZoom(scale, focusX, focusY, mScaleType);
    }

    /**
     * Set zoom to the specified scale. Image will be centered around the point
     * (focusX, focusY). These floats range from 0 to 1 and denote the focus point
     * as a fraction from the left and top of the view. For example, the top left
     * corner of the image would be (0, 0). And the bottom right corner would be (1, 1).
     *
     * @param scale
     * @param focusX
     * @param focusY
     * @param scaleType
     */
    public void setZoom(float scale, float focusX, float focusY, ScaleType scaleType) {
        //
        // setZoom can be called before the image is on the screen, but at this point,
        // image and view sizes have not yet been calculated in onMeasure. Thus, we should
        // delay calling setZoom until the view has been measured.
        //
        if (!onDrawReady) {
            delayedZoomVariables = new ZoomVariables(scale, focusX, focusY, scaleType);
            return;
        }

        if (scaleType != mScaleType) {
            setScaleType(scaleType);
        }
        resetZoom();
        scaleImage(scale, viewWidth / 2, viewHeight / 2, true);
        matrix.getValues(m);
        m[Matrix.MTRANS_X] = -((focusX * getImageWidth()) - (viewWidth * 0.5f));
        m[Matrix.MTRANS_Y] = -((focusY * getImageHeight()) - (viewHeight * 0.5f));
        matrix.setValues(m);
        fixTrans();
        setImageMatrix(matrix);
    }

    /**
     * Set zoom parameters equal to another TouchImageView. Including scale, position,
     * and ScaleType.
     *
     * @param
     */
    public void setZoom(TouchImageView img) {
        PointF center = img.getScrollPosition();
        setZoom(img.getCurrentZoom(), center.x, center.y, img.getScaleType());
    }

    /**
     * Return the point at the center of the zoomed image. The PointF coordinates range
     * in value between 0 and 1 and the focus point is denoted as a fraction from the left
     * and top of the view. For example, the top left corner of the image would be (0, 0).
     * And the bottom right corner would be (1, 1).
     *
     * @return PointF representing the scroll position of the zoomed image.
     */
    public PointF getScrollPosition() {
        Drawable drawable = getDrawable();
        if (drawable == null) {
            return null;
        }
        int drawableWidth = drawable.getIntrinsicWidth();
        int drawableHeight = drawable.getIntrinsicHeight();

        PointF point = transformCoordTouchToBitmap(viewWidth / 2, viewHeight / 2, true);
        point.x /= drawableWidth;
        point.y /= drawableHeight;
        return point;
    }

    /**
     * Set the focus point of the zoomed image. The focus points are denoted as a fraction from the
     * left and top of the view. The focus points can range in value between 0 and 1.
     *
     * @param focusX
     * @param focusY
     */
    public void setScrollPosition(float focusX, float focusY) {
        setZoom(normalizedScale, focusX, focusY);
    }

    /**
     * Performs boundary checking and fixes the image matrix if it
     * is out of bounds.
     */
    private void fixTrans() {
        matrix.getValues(m);
        float transX = m[Matrix.MTRANS_X];
        float transY = m[Matrix.MTRANS_Y];

        float fixTransX = getFixTrans(transX, viewWidth, getImageWidth());
        float fixTransY = getFixTrans(transY, viewHeight, getImageHeight());

        if (fixTransX != 0 || fixTransY != 0) {
            matrix.postTranslate(fixTransX, fixTransY);
        }
    }

    /**
     * When transitioning from zooming from focus to zoom from center (or vice versa)
     * the image can become unaligned within the view. This is apparent when zooming
     * quickly. When the content size is less than the view size, the content will often
     * be centered incorrectly within the view. fixScaleTrans first calls fixTrans() and
     * then makes sure the image is centered correctly within the view.
     */
    private void fixScaleTrans() {
        fixTrans();
        matrix.getValues(m);
        if (getImageWidth() < viewWidth) {
            m[Matrix.MTRANS_X] = (viewWidth - getImageWidth()) / 2;
        }

        if (getImageHeight() < viewHeight) {
            m[Matrix.MTRANS_Y] = (viewHeight - getImageHeight()) / 2;
        }
        matrix.setValues(m);
    }

    private float getFixTrans(float trans, float viewSize, float contentSize) {
        float minTrans, maxTrans;

        if (contentSize <= viewSize) {
            minTrans = 0;
            maxTrans = viewSize - contentSize;

        } else {
            minTrans = viewSize - contentSize;
            maxTrans = 0;
        }

        if (trans < minTrans)
            return -trans + minTrans;
        if (trans > maxTrans)
            return -trans + maxTrans;
        return 0;
    }

    private float getFixDragTrans(float delta, float viewSize, float contentSize) {
        if (contentSize <= viewSize) {
            return 0;
        }
        return delta;
    }

    private float getImageWidth() {
        return matchViewWidth * normalizedScale;
    }

    private float getImageHeight() {
        return matchViewHeight * normalizedScale;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        Drawable drawable = getDrawable();
        if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0) {
            setMeasuredDimension(0, 0);
            return;
        }

        int drawableWidth = drawable.getIntrinsicWidth();
        int drawableHeight = drawable.getIntrinsicHeight();
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        viewWidth = setViewSize(widthMode, widthSize, drawableWidth);
        viewHeight = setViewSize(heightMode, heightSize, drawableHeight);

        //
        // Set view dimensions
        //
        setMeasuredDimension(viewWidth, viewHeight);

        //
        // Fit content within view
        //
        fitImageToView();
    }

    /**
     * If the normalizedScale is equal to 1, then the image is made to fit the screen. Otherwise,
     * it is made to fit the screen according to the dimensions of the previous image matrix. This
     * allows the image to maintain its zoom after rotation.
     */
    private void fitImageToView() {
        Drawable drawable = getDrawable();
        if (drawable == null || drawable.getIntrinsicWidth() == 0 || drawable.getIntrinsicHeight() == 0) {
            return;
        }
        if (matrix == null || prevMatrix == null) {
            return;
        }

        int drawableWidth = drawable.getIntrinsicWidth();
        int drawableHeight = drawable.getIntrinsicHeight();

        //
        // Scale image for view
        //
        float scaleX = (float) viewWidth / drawableWidth;
        float scaleY = (float) viewHeight / drawableHeight;

        switch (mScaleType) {
            case CENTER:
                scaleX = scaleY = 1;
                break;

            case CENTER_CROP:
                scaleX = scaleY = Math.max(scaleX, scaleY);
                break;

            case CENTER_INSIDE:
                scaleX = scaleY = Math.min(1, Math.min(scaleX, scaleY));

            case FIT_CENTER:
                scaleX = scaleY = Math.min(scaleX, scaleY);
                break;

            case FIT_XY:
                break;

            default:
                //
                // FIT_START and FIT_END not supported
                //
                throw new UnsupportedOperationException("TouchImageView does not support FIT_START or FIT_END");

        }

        //
        // Center the image
        //
        float redundantXSpace = viewWidth - (scaleX * drawableWidth);
        float redundantYSpace = viewHeight - (scaleY * drawableHeight);
        matchViewWidth = viewWidth - redundantXSpace;
        matchViewHeight = viewHeight - redundantYSpace;
        if (!isZoomed() && !imageRenderedAtLeastOnce) {
            //
            // Stretch and center image to fit view
            //
            matrix.setScale(scaleX, scaleY);
            matrix.postTranslate(redundantXSpace / 2, redundantYSpace / 2);
            normalizedScale = 1;

        } else {
            //
            // These values should never be 0 or we will set viewWidth and viewHeight
            // to NaN in translateMatrixAfterRotate. To avoid this, call savePreviousImageValues
            // to set them equal to the current values.
            //
            if (prevMatchViewWidth == 0 || prevMatchViewHeight == 0) {
                savePreviousImageValues();
            }

            prevMatrix.getValues(m);

            //
            // Rescale Matrix after rotation
            //
            m[Matrix.MSCALE_X] = matchViewWidth / drawableWidth * normalizedScale;
            m[Matrix.MSCALE_Y] = matchViewHeight / drawableHeight * normalizedScale;

            //
            // TransX and TransY from previous matrix
            //
            float transX = m[Matrix.MTRANS_X];
            float transY = m[Matrix.MTRANS_Y];

            //
            // Width
            //
            float prevActualWidth = prevMatchViewWidth * normalizedScale;
            float actualWidth = getImageWidth();
            translateMatrixAfterRotate(Matrix.MTRANS_X, transX, prevActualWidth, actualWidth, prevViewWidth, viewWidth, drawableWidth);

            //
            // Height
            //
            float prevActualHeight = prevMatchViewHeight * normalizedScale;
            float actualHeight = getImageHeight();
            translateMatrixAfterRotate(Matrix.MTRANS_Y, transY, prevActualHeight, actualHeight, prevViewHeight, viewHeight, drawableHeight);

            //
            // Set the matrix to the adjusted scale and translate values.
            //
            matrix.setValues(m);
        }
        fixTrans();
        setImageMatrix(matrix);
    }

    /**
     * Set view dimensions based on layout params
     *
     * @param mode
     * @param size
     * @param drawableWidth
     * @return
     */
    private int setViewSize(int mode, int size, int drawableWidth) {
        int viewSize;
        switch (mode) {
            case MeasureSpec.EXACTLY:
                viewSize = size;
                break;

            case MeasureSpec.AT_MOST:
                viewSize = Math.min(drawableWidth, size);
                break;

            case MeasureSpec.UNSPECIFIED:
                viewSize = drawableWidth;
                break;

            default:
                viewSize = size;
                break;
        }
        return viewSize;
    }


    ........

Ref: https://gist.github.com/myinnos/e14b750be9503a2b2611f5a5a74a9e6c

As SOF limit to 30000 characters it may miss the last line of code, Please take the class from the above link.

Use it in your XML like:

<com.mypackagename.TouchImageView
            android:id="@+id/productImage"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:scaleType="fitCenter"/>

Answer 4

I have gone through almost 15+ libraries or JAVA classes so far to implement the pinch and double-tap zoom feature on ImageView. But PhotoView is the best I've used and implemented in terms of functionality and memory management. Go and check this. If it helps you, give an upvote so that others can use it.

Answer 5

Zoomable imageview with singletap listener

import android.content.Context;
import android.graphics.Rect;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

import it.sephiroth.android.library.imagezoom.ImageViewTouch;

public class MyZoomableImageViewTouch extends ImageViewTouch
{

    static final float SCROLL_DELTA_THRESHOLD = 1.0f;

    public MyZoomableImageViewTouch(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
        init();
    }

    public MyZoomableImageViewTouch(Context context, AttributeSet attrs) {
         super(context, attrs);
         init();
    }

    public MyZoomableImageViewTouch(Context context)
    {
        super(context);
        init();
    }

    private void init() {
        View.OnTouchListener listener = new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                 if (getScale() > 1f) {
                 getParent().requestDisallowInterceptTouchEvent(true);
                 } else {
                 getParent().requestDisallowInterceptTouchEvent(false);
                 }
                 return false;
            }
           };
           setOnTouchListener(listener);
           setDisplayType(DisplayType.FIT_TO_SCREEN);
     }

     @Override
    protected float onDoubleTapPost(float scale, float maxZoom) {
        if (scale != 1f) {
           mDoubleTapDirection = 1;
           return 1f;
       }
       if (mDoubleTapDirection == 1) {
            mDoubleTapDirection = -1;
          if ((scale + (mScaleFactor * 2)) <= maxZoom) {
              return scale + mScaleFactor;
          }   else {
              mDoubleTapDirection = -1;
              return maxZoom;
          }
        } else {
          mDoubleTapDirection = 1;
          return 1f;
       }
  }

    @Override
    public boolean canScroll(int direction) {
       RectF bitmapRect = getBitmapRect();
       updateRect(bitmapRect, mScrollRect);
       Rect imageViewRect = new Rect();
       getGlobalVisibleRect(imageViewRect);

       if (null == bitmapRect) {
          return false;
       }

       if (Math.abs(bitmapRect.right - imageViewRect.right) < SCROLL_DELTA_THRESHOLD) {
           if (direction < 0) {
                return false;
           }
       }

       if (Math.abs(bitmapRect.left - mScrollRect.left) <  SCROLL_DELTA_THRESHOLD) {
           if (direction > 0) {
               return false;
           }
       }
       return true;
   }

   @Override
   public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY)
   {
        if (getScale() == 1f) return false;
        if (distanceX != 0 && !canScroll((int) -distanceX)) {
             getParent().requestDisallowInterceptTouchEvent(false);
             return false;
        } else {
             getParent().requestDisallowInterceptTouchEvent(true);
             mUserScaled = true;
             scrollBy(-distanceX, -distanceY);
            invalidate();
            return true;
       }
   }
}

Use this method for single tap

    imageView.setSingleTapListener(new ImageViewTouch.OnImageViewTouchSingleTapListener()
    {
        @Override
        public void onSingleTapConfirmed()
        {
        }
     }

Answer 6

i know this is late but i have not seen any of the previous answers in kotlin

class ImageZoomingClass : AppCompatImageView, View.OnTouchListener,
GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener {
//shared constructing
private var mContext: Context? = null
private var mScaleDetector: ScaleGestureDetector? = null
private var mGestureDetector: GestureDetector? = null
var mMatrix: Matrix? = null
private var mMatrixValues: FloatArray? = null
var mode = NONE

// all possible state
companion object {
    const val NONE = 0
    const val DRAG = 1
    const val ZOOM = 2
}

// Scales
var mSaveScale = 1f
var mMinScale = 1f
var mMaxScale = 4f

// view dimensions
var origWidth = 0f
var origHeight = 0f
var viewWidth = 0
var viewHeight = 0
private var mLast = PointF()
private var mStart = PointF()

constructor(context: Context) : super(context) {
    sharedConstructing(context)
}

constructor(context: Context, @Nullable attrs: AttributeSet?) : super(context, attrs) {
    sharedConstructing(context)
}

constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(
    context!!,
    attrs,
    defStyleAttr
)

private fun sharedConstructing(context: Context) {
    super.setClickable(true)
    mContext = context
    mScaleDetector = ScaleGestureDetector(context, ScaleListener())
    mMatrix = Matrix()
    mMatrixValues = FloatArray(9)
    imageMatrix = mMatrix
    scaleType = ScaleType.MATRIX
    mGestureDetector = GestureDetector(context, this)
    setOnTouchListener(this)
}

private inner class ScaleListener : ScaleGestureDetector.SimpleOnScaleGestureListener() {
    override fun onScaleBegin(detector: ScaleGestureDetector): Boolean {
        mode = ZOOM
        return true
    }

    override fun onScale(detector: ScaleGestureDetector): Boolean {
        var mScaleFactor = detector.scaleFactor
        val prevScale = mSaveScale
        mSaveScale *= mScaleFactor
        if (mSaveScale > mMaxScale) {
            mSaveScale = mMaxScale
            mScaleFactor = mMaxScale / prevScale
        } else if (mSaveScale < mMinScale) {
            mSaveScale = mMinScale
            mScaleFactor = mMinScale / prevScale
        }
        if (origWidth * mSaveScale <= viewWidth
            || origHeight * mSaveScale <= viewHeight
        ) {
            mMatrix!!.postScale(
                mScaleFactor, mScaleFactor, viewWidth / 2.toFloat(),
                viewHeight / 2.toFloat()
            )
        } else {
            mMatrix!!.postScale(
                mScaleFactor, mScaleFactor,
                detector.focusX, detector.focusY
            )
        }
        fixTranslation()
        return true
    }
}

private fun fitToScreen() {
    mSaveScale = 1f
    val scale: Float
    val drawable = drawable
    if (drawable == null || drawable.intrinsicWidth == 0 || drawable.intrinsicHeight == 0) return
    val imageWidth = drawable.intrinsicWidth
    val imageHeight = drawable.intrinsicHeight
    val scaleX = viewWidth.toFloat() / imageWidth.toFloat()
    val scaleY = viewHeight.toFloat() / imageHeight.toFloat()
    scale = scaleX.coerceAtMost(scaleY)
    mMatrix!!.setScale(scale, scale)

    // Center the image
    var redundantYSpace = (viewHeight.toFloat()
            - scale * imageHeight.toFloat())
    var redundantXSpace = (viewWidth.toFloat()
            - scale * imageWidth.toFloat())
    redundantYSpace /= 2.toFloat()
    redundantXSpace /= 2.toFloat()
    mMatrix!!.postTranslate(redundantXSpace, redundantYSpace)
    origWidth = viewWidth - 2 * redundantXSpace
    origHeight = viewHeight - 2 * redundantYSpace
    imageMatrix = mMatrix
}

fun fixTranslation() {
    mMatrix!!.getValues(mMatrixValues) //put matrix values into a float array so we can analyze
    val transX =
        mMatrixValues!![Matrix.MTRANS_X] //get the most recent translation in x direction
    val transY =
        mMatrixValues!![Matrix.MTRANS_Y] //get the most recent translation in y direction
    val fixTransX = getFixTranslation(transX, viewWidth.toFloat(), origWidth * mSaveScale)
    val fixTransY = getFixTranslation(transY, viewHeight.toFloat(), origHeight * mSaveScale)
    if (fixTransX != 0f || fixTransY != 0f) mMatrix!!.postTranslate(fixTransX, fixTransY)
}

private fun getFixTranslation(trans: Float, viewSize: Float, contentSize: Float): Float {
    val minTrans: Float
    val maxTrans: Float
    if (contentSize <= viewSize) { // case: NOT ZOOMED
        minTrans = 0f
        maxTrans = viewSize - contentSize
    } else { //CASE: ZOOMED
        minTrans = viewSize - contentSize
        maxTrans = 0f
    }
    if (trans < minTrans) { // negative x or y translation (down or to the right)
        return -trans + minTrans
    }
    if (trans > maxTrans) { // positive x or y translation (up or to the left)
        return -trans + maxTrans
    }
    return 0F
}

private fun getFixDragTrans(delta: Float, viewSize: Float, contentSize: Float): Float {
    return if (contentSize <= viewSize) {
        0F
    } else delta
}

override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec)
    viewWidth = MeasureSpec.getSize(widthMeasureSpec)
    viewHeight = MeasureSpec.getSize(heightMeasureSpec)
    if (mSaveScale == 1f) {

        // Fit to screen.
        fitToScreen()
    }
}

//OnTouch
override fun onTouch(view: View?, event: MotionEvent): Boolean {
    mScaleDetector!!.onTouchEvent(event)
    mGestureDetector!!.onTouchEvent(event)
    val currentPoint = PointF(event.x, event.y)
    when (event.action) {
        MotionEvent.ACTION_DOWN -> {
            mLast.set(currentPoint)
            mStart.set(mLast)
            mode = DRAG
        }
        MotionEvent.ACTION_MOVE -> if (mode == DRAG) {
            val dx = currentPoint.x - mLast.x
            val dy = currentPoint.y - mLast.y
            val fixTransX = getFixDragTrans(dx, viewWidth.toFloat(), origWidth * mSaveScale)
            val fixTransY = getFixDragTrans(dy, viewHeight.toFloat(), origHeight * mSaveScale)
            mMatrix!!.postTranslate(fixTransX, fixTransY)
            fixTranslation()
            mLast[currentPoint.x] = currentPoint.y
        }
        MotionEvent.ACTION_POINTER_UP -> mode = NONE
    }
    invalidate()
    imageMatrix = mMatrix
    return false
}

//GestureListener
override fun onDown(motionEvent: MotionEvent): Boolean {
    return false
}

override fun onShowPress(motionEvent: MotionEvent) {}
override fun onSingleTapUp(motionEvent: MotionEvent): Boolean {
    return false
}

override fun onScroll(
    motionEvent: MotionEvent,
    motionEvent1: MotionEvent,
    v: Float,
    v1: Float
): Boolean {
    return false
}

override fun onLongPress(motionEvent: MotionEvent) {}
override fun onFling(
    motionEvent: MotionEvent,
    motionEvent1: MotionEvent,
    v: Float,
    v1: Float
): Boolean {
    return false
}

//onDoubleTap
override fun onSingleTapConfirmed(motionEvent: MotionEvent): Boolean {
    return false
}

// zoom the image
// double tap again to return to normal
override fun onDoubleTap(e: MotionEvent): Boolean {
    // Double tap is detected
    Log.i("MAIN_TAG", "Double tap detected")
    val origScale = mSaveScale
    val mScaleFactor: Float
    if (mSaveScale == mMaxScale) {
        mSaveScale = mMinScale
        mScaleFactor = mMinScale / origScale
    } else {
        mSaveScale = mMaxScale
        mScaleFactor = mMaxScale / origScale
    }
    mMatrix?.postScale(
        mScaleFactor, mScaleFactor, (viewWidth / 2).toFloat(), (
                viewHeight / 2).toFloat()
    )
    fixTranslation()
    return false
}

override fun onDoubleTapEvent(motionEvent: MotionEvent): Boolean {
    return false
}

}

and your xml layout should look like this

<com.example.imagezooming.ImageZoomingClass
    android:id="@+id/largeImage"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="2dp"
    android:layout_marginEnd="2dp"
    android:clickable="true"
    android:focusable="true"
    android:src="@drawable/theImageYouWant"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

happy Coding!!!