Ich versuche, das Zoomen und Ziehen mit dem Gesten- und Skalen-Listener von Android zu implementieren. Das Problem ist, dass das Bild (das ich zu zoomen versuche) bei der Ausführung des Pinch-Zooms an einer bestimmten Stelle abprallt. Auch die Zoomposition ist nicht zentriert. Der folgende Code zeigt, was ich erreichen möchte. Irgendeine Idee, warum das Bild springt (und wie man es korrigiert)?

public class CustomView extends View {
    Bitmap image;
    int screenHeight;
    int screenWidth;
    Paint paint;
    GestureDetector gestures;
    ScaleGestureDetector scaleGesture;
    float scale = 1.0f;
    float horizontalOffset, verticalOffset;

    int NORMAL = 0;
    int ZOOM = 1;
    int DRAG = 2;
    boolean isScaling = false;
    float touchX, touchY;
        int mode = NORMAL;

    public CustomView(Context context) {
    super(context);
            //initializing variables
    image = BitmapFactory.decodeResource(getResources(),
            R.drawable.image_name);
            //This is a full screen view
    screenWidth = getResources().getDisplayMetrics().widthPixels;
    screenHeight = getResources().getDisplayMetrics().heightPixels;
    paint = new Paint();
    paint.setAntiAlias(true);
    paint.setFilterBitmap(true);
    paint.setDither(true);
    paint.setColor(Color.WHITE);

    scaleGesture = new ScaleGestureDetector(getContext(),
            new ScaleListener());
    gestures = new GestureDetector(getContext(), new GestureListener());
    mode = NORMAL;
    initialize();
}

//Best fit image display on canvas 
    private void initialize() {
    float imgPartRatio = image.getWidth() / (float) image.getHeight();
    float screenRatio = (float) screenWidth / (float) screenHeight;

    if (screenRatio > imgPartRatio) {
        scale = ((float) screenHeight) / (float) (image.getHeight()); // fit height
        horizontalOffset = ((float) screenWidth - scale
                * (float) (image.getWidth())) / 2.0f;
        verticalOffset = 0;
    } else {
        scale = ((float) screenWidth) / (float) (image.getWidth()); // fit width
        horizontalOffset = 0;
        verticalOffset = ((float) screenHeight - scale
                * (float) (image.getHeight())) / 2.0f;
    }
        invalidate();
}

@Override
protected void onDraw(Canvas canvas) {
    canvas.save();
    canvas.drawColor(0, Mode.CLEAR);
    canvas.drawColor(Color.WHITE);
    if(mode == DRAG || mode == NORMAL) {
        //This works perfectly as expected
        canvas.translate(horizontalOffset, verticalOffset);
        canvas.scale(scale, scale);
        canvas.drawBitmap(image, getMatrix(), paint);
    }
    else if (mode == ZOOM) {
        //PROBLEM AREA - when applying pinch zoom,
        //the image jumps to a position abruptly
        canvas.scale(scale, scale, touchX, touchY);
        canvas.drawBitmap(image, getMatrix(), paint);
    }
    canvas.restore();
}

public class ScaleListener implements OnScaleGestureListener {
    @Override
    public boolean onScale(ScaleGestureDetector detector) {
        float scaleFactorNew = detector.getScaleFactor();
        if (detector.isInProgress()) {
            touchX = detector.getFocusX();
            touchY = detector.getFocusY();
            scale *= scaleFactorNew;
            invalidate(0, 0, screenWidth, screenHeight);
        }
        return true;
    }

    @Override
    public boolean onScaleBegin(ScaleGestureDetector detector) {
        isScaling = true;
        mode=ZOOM;
        return true;
    }

    @Override
    public void onScaleEnd(ScaleGestureDetector detector) {
        mode = NORMAL;
        isScaling = false;
    }

}

public class GestureListener implements GestureDetector.OnGestureListener,
        GestureDetector.OnDoubleTapListener {

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

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
            float distanceX, float distanceY) {
        if (!isScaling) {
            mode = DRAG;
            isScaling = false;
            horizontalOffset -= distanceX;
            verticalOffset -= distanceY;
            invalidate(0, 0, screenWidth, screenHeight);
        } else {
            mode = ZOOM;
            isScaling = true;
        }
        return true;
    }
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    scaleGesture.onTouchEvent(event);
    gestures.onTouchEvent(event);
    return true;
}
}

Danke im Voraus.