Android视图不响应绘制

Question

I'm currently experimenting with my first custom View in android and have been trying to draw points on a canvas via a onTouchEvent but have failed after several attempts. The View does detect my touches and successfully prints out a System.out.println message when touched however it still doesn't draw on the canvas.

After several various attempts this is what I came up with:

package com.techdigy.testapp;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class DrawingBoard extends View {
    Canvas canvas;
    Bitmap bmp;
    BitmapDrawable temp;

    public DrawingBoard(Context context, AttributeSet attributeSet) {
        super(context,attributeSet);
        // TODO Auto-generated constructor stub     
    }
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        bmp = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        canvas = new Canvas();
        }

    protected void onDraw(Canvas canvas) {
        //draw view
        }
    public boolean onTouchEvent(MotionEvent event) {
        //detect user touch
        float touchX = event.getX();
        float touchY = event.getY();
        Paint paint = new Paint();
        System.out.println("test");
        this.canvas.drawPoint(touchX, touchY, paint);
        temp = new BitmapDrawable(this.bmp);
        this.setBackground(this.temp);
        invalidate();
        return true;
        }
}

Answer 1

Use this code for draw point or any thing on canvas...

public class signature extends View {
        private static final float STROKE_WIDTH = 5f;
        private static final float HALF_STROKE_WIDTH = STROKE_WIDTH / 2;
        private Paint paint = new Paint();
        private Path path = new Path();

        private float lastTouchX;
        private float lastTouchY;
        private final RectF dirtyRect = new RectF();

        public signature(Context context, AttributeSet attrs) {
            super(context, attrs);
            paint.setAntiAlias(true);
            paint.setColor(Color.BLACK);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeJoin(Paint.Join.ROUND);
            paint.setStrokeWidth(STROKE_WIDTH);
        }

        public void save(View v) {
            Log.v("log_tag", "Width: " + v.getWidth());
            Log.v("log_tag", "Height: " + v.getHeight());
            if (mBitmap == null) {
                mBitmap = Bitmap.createBitmap(mContent.getWidth(),
                        mContent.getHeight(), Bitmap.Config.RGB_565);
                ;
            }
            Canvas canvas = new Canvas(mBitmap);
            try {
                FileOutputStream mFileOutStream = new FileOutputStream(new File(Environment.getExternalStorageDirectory().toString()
                        , "sign.png"));

                v.draw(canvas);
                mBitmap.compress(Bitmap.CompressFormat.PNG, 90, mFileOutStream);
                mFileOutStream.flush();
                mFileOutStream.close();
                String url = Images.Media.insertImage(getContentResolver(),
                        mBitmap, "title", null);
                Log.v("log_tag", "url: " + url);
                // In case you want to delete the file
                // boolean deleted = mypath.delete();
                // Log.v("log_tag","deleted: " + mypath.toString() + deleted);
                // If you want to convert the image to string use base64
                // converter

            } catch (Exception e) {
                Log.v("log_tag", e.toString());
            }
        }

        public void clear() {
            path.reset();
            invalidate();
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawPath(path, paint);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float eventX = event.getX();
            float eventY = event.getY();
            mGetSign.setEnabled(true);

            switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(eventX, eventY);
                lastTouchX = eventX;
                lastTouchY = eventY;
                return true;

            case MotionEvent.ACTION_MOVE:

            case MotionEvent.ACTION_UP:

                resetDirtyRect(eventX, eventY);
                int historySize = event.getHistorySize();
                for (int i = 0; i < historySize; i++) {
                    float historicalX = event.getHistoricalX(i);
                    float historicalY = event.getHistoricalY(i);
                    expandDirtyRect(historicalX, historicalY);
                    path.lineTo(historicalX, historicalY);
                }
                path.lineTo(eventX, eventY);
                break;

            default:
                debug("Ignored touch event: " + event.toString());
                return false;
            }

            invalidate((int) (dirtyRect.left - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.top - HALF_STROKE_WIDTH),
                    (int) (dirtyRect.right + HALF_STROKE_WIDTH),
                    (int) (dirtyRect.bottom + HALF_STROKE_WIDTH));

            lastTouchX = eventX;
            lastTouchY = eventY;

            return true;
        }

        private void debug(String string) {
        }

        private void expandDirtyRect(float historicalX, float historicalY) {
            if (historicalX < dirtyRect.left) {
                dirtyRect.left = historicalX;
            } else if (historicalX > dirtyRect.right) {
                dirtyRect.right = historicalX;
            }

            if (historicalY < dirtyRect.top) {
                dirtyRect.top = historicalY;
            } else if (historicalY > dirtyRect.bottom) {
                dirtyRect.bottom = historicalY;
            }
        }

        private void resetDirtyRect(float eventX, float eventY) {
            dirtyRect.left = Math.min(lastTouchX, eventX);
            dirtyRect.right = Math.max(lastTouchX, eventX);
            dirtyRect.top = Math.min(lastTouchY, eventY);
            dirtyRect.bottom = Math.max(lastTouchY, eventY);
        }
    }

Answer 2

try this...

public class DrawingBoard extends View {
    private Bitmap bmp;
    private float touchX;
    private float touchY;
    private Paint paint;
    public DrawingBoard(Context context, AttributeSet attributeSet) {
        super(context, attributeSet);
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setColor(Color.GREEN);
        paint.setStyle(Paint.Style.STROKE);
    }

    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        bmp = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        setBackgroundDrawable(new BitmapDrawable(getResources(), bmp));
    }

    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawPoint(touchX, touchY, paint);
    }

    public boolean onTouchEvent(MotionEvent event) {
        // detect user touch
        touchX = event.getX();
        touchY = event.getY();
        System.out.println("test");
        invalidate();
        return true;
    }
}