使用scaleFocus缩放画布会导致跳转

Question

我正在开发一个自定义视图,可以使用缩放手势进行缩放.当我没有使用比例焦点时,一切正常.但是,一旦我这样做canvas.scale(mScaleFactor, mScaleFactor, scaleFocus[0], scaleFocus[1]);,它会导致跳跃,同时缩小到一些低比例因子.这是视图的简化版本,它说明了问题:

public class TestView extends FrameLayout {

private ScaleGestureDetector mScaleGestureDetector;
private float mScaleFactor = 1.f;
private float mMinScaleFactor = 0.4f;
private static final float MAX_SCALE_FACTOR = 2.0f;
private Matrix canvasMatrix = new Matrix();
float[] scaleFocus = new float[2];
private Rect clipBounds = new Rect();

private static final String TAG = "TestView";

public TestView(@NonNull Context context) {
    super(context);
    sharedConstructor();
}

public TestView(@NonNull Context context, @Nullable AttributeSet attrs) {
    super(context, attrs);
    sharedConstructor();
}

public TestView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
    super(context, attrs, defStyleAttr);
    sharedConstructor();
}

public void setChildViews() {
    ImageView imageView = new ImageView(getContext());
    LayoutParams layoutParams = new LayoutParams(StateUtil.screenWidth*2, StateUtil.screenHeight*2);
    layoutParams.gravity = Gravity.CENTER;
    imageView.setLayoutParams(layoutParams);
    imageView.setImageResource(R.drawable.test);
    canvasMatrix.set(getMatrix());

    addView(imageView);

    //some additional views are added here
}

private void sharedConstructor(){
    mScaleGestureDetector = new ScaleGestureDetector(getContext(), mScaleGestureListener);

    setChildViews();
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    return mScaleGestureDetector.onTouchEvent(event) || super.onTouchEvent(event);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    canvas.getClipBounds(clipBounds);
    canvas.scale(mScaleFactor, mScaleFactor, scaleFocus[0], scaleFocus[1]);

    canvas.getMatrix().invert(canvasMatrix);
    canvas.save();
}

private final ScaleGestureDetector.OnScaleGestureListener mScaleGestureListener
        = new ScaleGestureDetector.SimpleOnScaleGestureListener() {

    @Override
    public boolean onScale(ScaleGestureDetector detector) {

        scaleFocus[0] = detector.getFocusX();
        scaleFocus[1] = detector.getFocusY();

        canvasMatrix.mapPoints(scaleFocus);
        if (clipBounds.contains((int) scaleFocus[0], (int) scaleFocus[1])){
            mScaleFactor *= detector.getScaleFactor();
            mScaleFactor = Math.max(mMinScaleFactor, Math.min(mScaleFactor, MAX_SCALE_FACTOR));
            TestView.this.invalidate();
        }

        return true;
    }
};

}

这是我的设备上的样子:

我已经尝试过这个答案的解决方案,但它对我不起作用.即使我不打电话super.onTouchEvent(event);,问题仍然存在.

是什么原因导致它以及如何解决？