Android ImageView的拖拽实现

在Android中我们可以通过对ImageView的ontouch事件进行监听，然后重新layout imageview来拖动它。这种情况下源ImageView也会跟着动。我们如果想实现源ImageView不动而有拖拽效果可以结合OnTouchListener 和 OnDragListener。、 我们对ImageView设置OnTouchListener 事件，对这个ImageView要拖到的目的区域设置OnDragListener事件。下面贴下代码。

/**
* Touch 事件
*/
final OnTouchListener movingEventListener = new OnTouchListener() {
private int downX;
private int downY;

public boolean onTouch(View view, MotionEvent motionEvent) {
int id = view.getId();
if (Constant.isScanning
&& (id == R.id.image_picture || id == R.id.image_file
|| id == R.id.image_music || id == R.id.image_video)) {

Toast.makeText(Constant.applicationContext, "正在扫描SDCard，请稍后。",
Toast.LENGTH_SHORT).show();
return false;

}
switch (motionEvent.getAction()) {
case MotionEvent.ACTION_DOWN:
downX = (int) motionEvent.getX();
downY = (int) motionEvent.getY();
break;
case MotionEvent.ACTION_MOVE:
int moveX = (int) motionEvent.getX();
int moveY = (int) motionEvent.getY();
int deltaY = moveY - downY;

if (Math.abs(deltaY) > 20) {
ClipData data = ClipData.newPlainText("", "");
DragShadowBuilder shadowBuilder = new View.DragShadowBuilder(
view);
view.startDrag(data, shadowBuilder, view, 0);

return true;
}
break;
}
return false;

}
};

picture.setOnTouchListener(movingEventListener);

picture 是要拖拽的ImageView的实例。对其设置onTouchListener监听事件，如果deltaY的绝对值大于20我们会触发它的拖拽动作。

/**
* 拖拽事件
*
* @Package com.example.privatecloud
* @ClassName: DragListener
* @date 2013-8-1 上午11:04:48
*/
class DragListener implements OnDragListener {
Drawable enterShape = getResources().getDrawable(
R.drawable.shape_droptarget);
Drawable normalShape = getResources().getDrawable(R.drawable.shape);

@Override
public boolean onDrag(View v, DragEvent event) {
int action = event.getAction();
switch (event.getAction()) {
case DragEvent.ACTION_DRAG_STARTED:
// Do nothing
break;
case DragEvent.ACTION_DRAG_ENTERED:
v.setBackgroundDrawable(enterShape);
break;
case DragEvent.ACTION_DRAG_EXITED:
v.setBackgroundDrawable(normalShape);
break;
case DragEvent.ACTION_DROP:
// Dropped, reassign View to ViewGroup
View view = (View) event.getLocalState();
// ViewGroup owner = (ViewGroup) view.getParent();
// owner.removeView(view);
// RelativeLayout container = (RelativeLayout) v;
// container.addView(view);

startTransmiss(view);
view.setVisibility(View.VISIBLE);
break;
case DragEvent.ACTION_DRAG_ENDED:
v.setBackgroundDrawable(normalShape);
default:
break;
}
return true;
}
}

serverLayout.setOnDragListener(new DragListener());

serverLayout就是我们的ImageView要拖拽的目的区域，在ACTION_DROP这个事件时，我们可以执行拖拽成功的操作了。