【Android__WebView】多点触摸实现缩放和拖拽图片

http://www.4byte.cn/question/634906/android-webview-can-t-be-scrolled-after-being-set-to-a-touch-listener.html

在MotionEvent中有两个事件值得注意一下，分别是ACTION_DOWN和ACTION_POINTER_DOWN。

ACTION_DOWN：这个很好理解，当屏幕检测到有手指按下之后就触发到这个事件。

ACTION_POINTER_DOWN：这个是实现多点的关键，当屏幕检测到有多个手指同时按下之后，就触发了这个事件。

通过getAction()可以获得当前屏幕的事件类型：ACTION_DOWN, ACTION_MOVE, ACTION_UP, or ACTION_CANCEL。但是如果像获得如上的ACTION_POINTER_DOWN，则得和ACTION_MASK相与才能得到ACTION_POINTER_DOWN事件。

@Override
        public boolean onTouch(View v, MotionEvent event) {
                ImageView view = (ImageView) v;
                dumpEvent(event);
                // Handle touch events here...
                switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:
                        matrix.set(view.getImageMatrix());
                        savedMatrix.set(matrix);
                        start.set(event.getX(), event.getY());
                        //Log.d(TAG, "mode=DRAG");
                        mode = DRAG;
                        //Log.d(TAG, "mode=NONE");
                        break;
                case MotionEvent.ACTION_POINTER_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");
                        }// ACTION_DOWN, ACTION_MOVE, ACTION_UP, or ACTION_CANCEL.
                        break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_POINTER_UP:
                        mode = NONE;
                        break;
                case MotionEvent.ACTION_MOVE:
                        if (mode == DRAG) {
                                // ...
                                matrix.set(savedMatrix);
                                matrix.postTranslate(event.getX() - start.x, event.getY()
                                                - start.y);
                        } else if (mode == ZOOM) {
                                float newDist = spacing(event);
                                //Log.d(TAG, "newDist=" + newDist);
                                if (newDist > 10f) {
                                        matrix.set(savedMatrix);
                                        float scale = newDist / oldDist;
                                        matrix.postScale(scale, scale, mid.x, mid.y);
                                }
                        }
                        break;
                }

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

        private void dumpEvent(MotionEvent event) {
                String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
                                "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
                StringBuilder sb = new StringBuilder();
                int action = event.getAction();
                int actionCode = action & MotionEvent.ACTION_MASK;
                sb.append("event ACTION_").append(names[actionCode]);
                if (actionCode == MotionEvent.ACTION_POINTER_DOWN
                                || actionCode == MotionEvent.ACTION_POINTER_UP) {
                        sb.append("(pid ").append(
                                        action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
                        sb.append(")");
                }
                sb.append("[");
                for (int i = 0; i < event.getPointerCount(); i++) {
                        sb.append("#").append(i);
                        sb.append("(pid ").append(event.getPointerId(i));
                        sb.append(")=").append((int) event.getX(i));
                        sb.append(",").append((int) event.getY(i));
                        if (i + 1 < event.getPointerCount())
                                sb.append(";");
                }
                sb.append("]");
                //Log.d(TAG, sb.toString());
        } 

/**
 * 求两点间距离：
 */
private float spacing(MotionEvent event) {
	float x = event.getX(0) - event.getX(1);
	float y = event.getY(0) - event.getY(1);
	return FloatMath.sqrt(x * x + y * y);
}
/**
 * 求两点间中点
 */
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);
}

将以上代码写到MulitPointTouchListener .java中，然后对你相应的图片进行OnTouchListener
比如：imageView.setOnTouchListener(new MulitPointTouchListener ());在xml中要将图片的缩放格式改成Matrix