Android 捏合缩放

Android 捏合缩放：提升用户体验的交互方式

xml
    android:id="@+id/imageView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:src="@drawable/image" />

java
ImageView imageView = findViewById(R.id.imageView);
imageView.setOnTouchListener(new View.OnTouchListener() {
    private float scaleFactor = 1.0f;
    private float lastScaleFactor = 1.0f;
    @Override
    public boolean onTouch(View v, MotionEvent event) {
        int action = event.getActionMasked();
        int pointerCount = event.getPointerCount();
        switch (action) {
            case MotionEvent.ACTION_POINTER_DOWN:
                lastScaleFactor = scaleFactor;
                break;
            case MotionEvent.ACTION_MOVE:
                if (pointerCount == 2) {
                    float currentDistance = getDistance(event);
                    scaleFactor = lastScaleFactor * (currentDistance / initialDistance);
                    imageView.setScaleX(scaleFactor);
                    imageView.setScaleY(scaleFactor);
                }
                break;
            case MotionEvent.ACTION_POINTER_UP:
                lastScaleFactor = scaleFactor;
                break;
        }
        return true;
    }
    private float getDistance(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);
    }
});