Question

所以我一直在为这一天做好准备。假设我有一个自定义的ImageView，我想覆盖在背景视图上（都在RelativeLayout中），当触摸时，它会擦除View的源位图部分，就像MS Paint中的擦除工具一样，暴露下面的View。我已经检查了几乎所有的线程（如this one），他们建议在Paint对象中使用PorterDuff SRC模式，并创建一个Canvas out out out源位图的ARGB_8888卷影副本以应用掩码。

此外，我不能提前设置叠加源，因为我必须通过网络下载它，以便ImageView的缩放类型为我处理缩放。

每当我覆盖onDraw时，当我在IV的位图上应用擦除时，它会显示黑色背景而不是下面的视图，即使我将背景设置为透明。所以我在最后一条绳子上知道如何揭开背景视图。

这是我到目前为止所拥有的：

view constructor：

    paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));  
    paint.setColor(Color.TRANSPARENT);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeJoin(Paint.Join.ROUND);
    paint.setStrokeWidth(STROKE_WIDTH);
    paint.setAntiAlias(true);

覆盖setImageBitmap以从重新配置的源位图设置我的画布：

public void setImageBitmap(Bitmap bitmap){
    super.setImageBitmap(bitmap);
    Drawable bd = getDrawable();
    if(bd == null){
        return;
    }

    Bitmap fullSizeBitmap = ((BitmapDrawable) bd).getBitmap();
    overlay = fullSizeBitmap.copy(Config.ARGB_8888, true);
    c2 = new Canvas(overlay);
}

onDraw方法：

protected void onDraw(Canvas canvas) {
    /*
     * Override paint call by re-drawing the view's Bitmap first, then overlaying our path on top of it
     */
    Drawable bd = getDrawable();
    if(bd == null){
        return;
    }
    Bitmap fullSizeBitmap = ((BitmapDrawable) bd).getBitmap();
    if(fullSizeBitmap != null && c2 != null){
        canvas.drawColor(Color.TRANSPARENT);
        c2.drawBitmap(fullSizeBitmap, 0, 0, null);
        c2.drawPath(path, paint);
        canvas.drawBitmap(overlay, 0, 0, null);
    }
}

Answer 1

我知道这是一个非常古老的问题，但这是我为解决我遇到的类似问题而采取的措施。也许它有助于未来的人。

从API级别11及以上，您必须为ImageView指定这段代码，以便在后面而不是黑色区域显示图像。

if (Build.VERSION.SDK_INT >= 11) {
    imageview.setLayerType(View.LAYER_TYPE_SOFTWARE, null);
}

这有助于我成功显示背面图像

Answer 2

你能尝试这个解决方案，它可以帮助你在触摸Android时删除图像..或下载demo example

public class MainActivity extends Activity {

    Bitmap bp;
    Canvas bitmapCanvas;
    DrawView drawImg;
    LinearLayout ln1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        ln1 = (LinearLayout) findViewById(R.id.ln1);
        drawImg = new DrawView(this);
        ln1.addView(drawImg);

    }



    public class DrawView extends View implements View.OnTouchListener {

        private int x = 0;
        private int y = 0;

        Bitmap bitmap;
        Path circlePath;
        Paint circlePaint;

        private final Paint paint = new Paint();
        private final Paint eraserPaint = new Paint();


        public DrawView(Context context){
            super(context);
            setFocusable(true);
            setFocusableInTouchMode(true);
            this.setOnTouchListener(this);

            // Set background
            this.setBackgroundColor(Color.CYAN);
            bp = BitmapFactory.decodeResource(getResources(), R.drawable.bg);

            // Set bitmap
            bitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
            bitmapCanvas = new Canvas();
            bitmapCanvas.setBitmap(bitmap);
            bitmapCanvas.drawColor(Color.TRANSPARENT);
            bitmapCanvas.drawBitmap(bp, 0, 0, null);

            circlePath = new Path();
            circlePaint = new Paint();
            circlePaint.setAntiAlias(true);
            circlePaint.setColor(Color.BLUE);
            circlePaint.setStyle(Paint.Style.STROKE);
            circlePaint.setStrokeJoin(Paint.Join.MITER);
            circlePaint.setStrokeWidth(4f);

            // Set eraser paint properties
            eraserPaint.setAlpha(0);
            eraserPaint.setStrokeJoin(Paint.Join.ROUND);
            eraserPaint.setStrokeCap(Paint.Cap.ROUND);
            eraserPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
            eraserPaint.setAntiAlias(true);

        }

        @Override
        public void onDraw(Canvas canvas) {

            canvas.drawBitmap(bitmap, 0, 0, paint);
            bitmapCanvas.drawCircle(x, y, 30, eraserPaint);

            canvas.drawPath(circlePath, circlePaint);
        }

        public boolean onTouch(View view, MotionEvent event) {
            x = (int) event.getX();
            y = (int) event.getY();

            bitmapCanvas.drawCircle(x, y, 30, eraserPaint);

            circlePath.reset();
            circlePath.addCircle(x, y, 30, Path.Direction.CW);

            int ac=event.getAction();
            switch(ac){
                case MotionEvent.ACTION_UP:
                    Toast.makeText(MainActivity.this, String.valueOf(x), Toast.LENGTH_SHORT).show();
                    circlePath.reset();
                    break;
            }
            invalidate();
            return true;
        }
    }
}

Android - 触摸以擦除前景ImageView的部分以显示背景视图

2 个答案: