Android自定义imageview具有类似webview的缩放

Question

i think this question has been asked quite often, but I couldn`t find an appropriate solution for my implementation. I built an custom imageview with an onScaleListener and an onGestureListener that scales and pans the containing image. The scaling is done with a matrix scaling. The function looks like that:

    @Override
    public boolean onScale(ScaleGestureDetector scaleGestureDetector) {
            scaleFactor *= scaleGestureDetector.getScaleFactor();
            scaleFactor = Math.max(initScale, Math.min(scaleFactor, initScale + 3.0f));
            matrix = getImageMatrix();
            matrix.setScale(scaleFactor, scaleFactor);
            matrix.getValues(values);
            matrix.postTranslate(-values[Matrix.MTRANS_X] + Math.max(0, centerX - centerImageX),
                    -values[Matrix.MTRANS_Y] + Math.max(0, centerY - centerImageY));
            setImageMatrix(matrix);
}

postTranslate() is needed to center the image if needed. To finish this I need to scroll to (scrollTo(x,y)) the position where the focus of the scaling gesture stays in the same position on the screen. At the end it should look like scaling in a webview. Can anybody help me with this?
When I use:
float scrollPosX = ((scrollwidth) * ((getScrollX() + touchX) / imagewidth));
float scrollPosY = ((scrollheight) * ((getScrollY() + touchY) / imageheight));
it will work for the first scaling, but when scaling in a scaled image it will scroll to the relative position. I think it is all related to the fact that I only get the touch position with getScrollX() and getScrollY() [it`s difficult to explain]

Answer 1

Now I found a solution that works for me. In my case I have to use the scaling step instead of the scaling factor.

                scrollTo((int) (getScrollX() - x + (scaleGestureDetector.getScaleFactor() * x) ),
                         (int) (getScrollY() - y + (scaleGestureDetector.getScaleFactor() * y) ));

with x and y as the touch position on the scaled image.