ImageView Drag Limitation In Android

Question

I have an ImageView in a layout and set OnTouchListener on ImageView to drag the ImageView. It\'s working perfectly. My problem is how can I prevent from move ImageView to out o

Answer 1

I used the answer from Benito Bertoli and modified the ACTION_MOVE code changing minor and major sign to make image zoom and drag for image zoomed

here´s the code

private static final float MIN_ZOOM = 1f; 
private static final float MAX_ZOOM = 2.5f; 

public boolean onTouch(View v, MotionEvent event) {
    ImageView view = (ImageView) v;
    view.setScaleType(ImageView.ScaleType.MATRIX);

    // Handle touch events here...
    switch (event.getAction() & MotionEvent.ACTION_MASK) {

        case MotionEvent.ACTION_DOWN: //first finger down only
            savedMatrix.set(matrix);
            start.set(event.getX(), event.getY());
            Log.d(TAG, "mode=DRAG" );
            mode = DRAG;
            break;
        case MotionEvent.ACTION_UP: //first finger lifted
        case MotionEvent.ACTION_POINTER_UP: //second finger lifted
            mode = NONE;
            Log.d(TAG, "mode=NONE" );
            break;
        case MotionEvent.ACTION_POINTER_DOWN: //second finger down
            oldDist = spacing(event);
            Log.d(TAG, "oldDist=" + oldDist);
            if (oldDist > 10f) {
                savedMatrix.set(matrix);
                midPoint(mid, event);
                mode = ZOOM;
                Log.d(TAG, "mode=ZOOM" );
            }
            break;
        case MotionEvent.ACTION_MOVE:
            if (mode == DRAG) {
                //matrix.set(savedMatrix);
                //matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);
                matrix.set(savedMatrix);

                matrix.getValues(matrixValues);
                matrixX = matrixValues[2];
                matrixY = matrixValues[5];
                width = matrixValues[0] * (view.getDrawable().getIntrinsicWidth());
                height = matrixValues[4] * (view.getDrawable().getIntrinsicHeight());


                dx = event.getX() - start.x;
                dy = event.getY() - start.y;

                //if image will go outside left bound
                if (matrixX + dx  > 0){
                    Log.e("dx","lef bound " + dx);
                    dx = -matrixX;
                }
                //if image will go outside right bound
                if(matrixX + dx + width < view.getWidth()){
                    dx = view.getWidth() - matrixX - width;
                }
                //if image will go oustside top bound
                if (matrixY + dy > 0){
                    dy = -matrixY;
                }
                //if image will go outside bottom bound
                if(matrixY + dy + height < view.getHeight()){
                    dy = view.getHeight() - matrixY - height;
                }

                matrix.postTranslate(dx, dy);
            }
            else if (mode == ZOOM) {
                Float newDist = spacing(event);
                Log.d(TAG, "newDist=" + newDist);
                if (newDist > 10f) {
                    matrix.set(savedMatrix);
                    float scale = newDist / oldDist;
                    float[] values = new float[9];
                    matrix.getValues(values);
                    float currentScale = values[Matrix.MSCALE_X];
                    if(scale * currentScale > MAX_ZOOM)
                        scale = MAX_ZOOM / currentScale;
                    else if (scale * currentScale < MIN_ZOOM)
                        scale = MIN_ZOOM / currentScale;
                    matrix.postScale(scale, scale, mid.x, mid.y);

                }
                break;
            }
    } //perform the transformation.

    view.setImageMatrix(matrix);
    return true; // indicate event was handled

}

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

    return drawable;
}