Android通过手势（多点）缩放和拖拽图片

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。

所以我们运用一个switch-case结构就可以实现对图片进行拖拽或缩放，而缩放的只要思想是在移动的过程中计算两个点之间的距离，然后再进行缩放。

上代码：

@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());

}

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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);

}

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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);

}

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还有一点要主要的是：ImageView在main.xml 设置为： android:scaleType="matrix"