我如何在 android 中使用 xy position 在图像上制作可移动的小点？

Question

I Have a image and i want to make a 8 dot on image, that dot are move when touch dot and drag to screen, is this possible to make that type of touch and movable dots on image?

Show above image on 8 point, i want to result like this image and also that point are move when you touch that point and move on image and also want that point x,y coordinate.

i tried below code but its show dots are not in proper form, and all dots move at the same time.

class DrawingView extends View {
        Bitmap bitmap;

        float x, y;

        public DrawingView(Context context) {
            super(context);
            bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_dot);
        }


        public boolean onTouchEvent(MotionEvent event) {

            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN: {

                }
                break;

                case MotionEvent.ACTION_MOVE: {
                    x = (int) event.getX();
                    y = (int) event.getY();

                    invalidate();
                }

                break;
                case MotionEvent.ACTION_UP:

                    x = (int) event.getX();
                    y = (int) event.getY();
                    System.out.println(".................." + x + "......" + y); //x= 345 y=530
                    invalidate();
                    break;
            }
            return true;
        }

        @Override
        public void onDraw(Canvas canvas) {
            Paint paint = new Paint();
            paint.setStyle(Paint.Style.FILL);
            paint.setColor(Color.WHITE);
           // canvas.drawBitmap(bitmap, x, y, paint);  //originally bitmap draw at x=o and y=0
            for (int i = 0; i < 8; i++) {
                canvas.drawBitmap(bitmap, x++, y++,  null);
            }
        }
    }

if anyone know about that type of view or any solution for it then help.

Thanks in advance:)

Answer 1

1. Create a custom ImageView which extends the androidx.appcompat.widget.AppCompatImageView class, which implements an OnTouchListener with an ArrayList<Dot> which will keep track of the Dot s.

2. You override onDraw(Canvas canvas) of the custom ImageView and iterate through the ArrayList of Dot s and draw each Dot in the list using canvas.drawCircle(float cx, float cy, float radius, @NonNull Paint paint) .

3. Whenever MotionEvent.ACTION_DOWN is fired you check if the touch was inside an existing dot.

   If it was you set that Dot to a global variable ie touchedDot , when the users moves OnTouchListener fires MotionEvent.ACTION_MOVE which you then check if touchedDot != null and if so simply change its x and y to match the events via touchedDot.x = event.getX() and touchedDot.y = event.getY() and then call invalidate() which will call the ImageView s onDraw method and the dot will be moved as the users finger moves. When the user lifts their finger either from a touch or a move, MotionEvent.ACTION_UP is fired, there you simply check if touchedDot == null and if so you then create a new Dot at the x and y they touched in, otherwise you set touchedDot = null to reset it for the next move or touch event.

Here is an example I created using Picasso to load the image into the custom ImageView :

build.gradle:

dependencies {
    ...
    implementation 'com.squareup.picasso:picasso:2.71828'
}

AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET" />

DrawableDotImageView.java:

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.ArrayList;

public class DrawableDotImageView extends androidx.appcompat.widget.AppCompatImageView implements View.OnTouchListener {

    private final ArrayList<Dot> dots = new ArrayList<>();
    private Paint dotPaint;
    private Dot touchedDot;

    public DrawableDotImageView(@NonNull Context context) {
        super(context);
        setup();
    }

    public DrawableDotImageView(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        setup();
    }

    public DrawableDotImageView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        setup();
    }

    private void setup() {
        setOnTouchListener(this);
        dotPaint = new Paint();
        dotPaint.setColor(Color.WHITE);
        dotPaint.setAlpha(100);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        dots.forEach((dot) -> {
            canvas.drawCircle(dot.getX(), dot.getY(), dot.getRadius(), dotPaint);
            Log.d("ImageView", "Drawing X: " + dot.x + " Y: " + dot.y);
        });
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                dots.forEach((dot) -> {
                    if (dot.isInside(event.getX(), event.getY())) {
                        touchedDot = dot;
                        Log.d("ImageView", "Dot touched");
                    }
                });
                break;
            case MotionEvent.ACTION_MOVE:
                if (touchedDot != null) {
                    touchedDot.x = event.getX();
                    touchedDot.y = event.getY();
                    invalidate();
                    Log.d("ImageView", "Dot moving X: " + touchedDot.x + " Y: " + touchedDot.y);
                }
                break;
            case MotionEvent.ACTION_UP:
                if (touchedDot != null) {
                    touchedDot = null;
                } else {
                    dots.add(new Dot(event.getX(), event.getY(), 35));
                    invalidate();
                    Log.d("ImageView", "Dot created X: " + event.getX() + " Y: " + event.getY());
                }
                break;
            case MotionEvent.ACTION_CANCEL:
                break;
            default:
                break;
        }
        return true;
    }

    private static class Dot {
        private float x;
        private float y;
        private final float radius;

        public Dot(float x, float y, float radius) {
            this.x = x;
            this.y = y;
            this.radius = radius;
        }

        public float getX() {
            return x;
        }

        public float getY() {
            return y;
        }

        public float getRadius() {
            return radius;
        }

        //https://www.geeksforgeeks.org/find-if-a-point-lies-inside-or-on-circle/
        public boolean isInside(float x, float y) {
            return (getX() - x) * (getX() - x) + (getY() - y) * (getY() - y) <= radius * radius;
        }
    }
}

TestFrament.xml: (change package name according to your own)

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.example.myapplicationjava.DrawableDotImageView
        android:id="@+id/imageView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitXY" />

</androidx.constraintlayout.widget.ConstraintLayout>

TestFrament.java:

@Override
public void onViewCreated(@NonNull View view, Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    DrawableDotImageView imageView = view.findViewById(R.id.imageView);
    Picasso.get().load("https://i.pinimg.com/originals/d4/d8/a0/d4d8a016155f00165411066bb9a0ab42.jpg").into(imageView);
}

Which produces: