本帖最后由 李小然 于 2014-5-16 14:24 编辑
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());
}
/**
* 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);
} |
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