在Android中使用RelativeLayout的onTouchListener的奇怪跳跃值

Question

I wrote the following function in order to drag around an ImageView on the screen. Seems to work alright except while dragging the image jumps around like crazy.

Looking at the log the problem seems to be I'm getting incorrect values for X and Y in between every correct value. I'm not sure why though. Can anyone help me fix this?

hereOnTouchListener imageListener = new OnTouchListener(){

@Override
public boolean onTouch(View v, MotionEvent event) {

  // TODO Auto-generated method stub
  int eventAction = event.getAction();

  int X = (int)event.getX();
  int Y = (int)event.getY();
  if (eventAction == MotionEvent.ACTION_DOWN){
   dragging = true;
   tempParams = new RelativeLayout.LayoutParams(v.getWidth(), v.getHeight());
Log.i("v width and height", v.getWidth() + " " + v.getHeight());
  }     
  if (eventAction == MotionEvent.ACTION_UP){
   Log.i("dragging up","dragging up" + X + " " + Y);
   dragging = false;
  } else if (eventAction == MotionEvent.ACTION_MOVE){
   if (dragging){
    Log.i("dragging","dragging " + X + " " + Y);
    tempParams.leftMargin = X;
    tempParams.topMargin = Y;
    v.setLayoutParams(tempParams);
   // v.setPadding(X, Y, 0, 0);
    v.invalidate();
   }
  }


  return true;
 }

};

sample of log output:

11-27 19:43:34.484: INFO/dragging(3530): dragging 131 131
11-27 19:43:34.504: INFO/dragging(3530): dragging 84 288
11-27 19:43:34.519: INFO/dragging(3530): dragging 132 134
11-27 19:43:34.539: INFO/dragging(3530): dragging 84 292
11-27 19:43:34.554: INFO/dragging(3530): dragging 132 139
11-27 19:43:34.574: INFO/dragging(3530): dragging 84 294
11-27 19:43:34.594: INFO/dragging(3530): dragging 132 142
11-27 19:43:34.609: INFO/dragging(3530): dragging 84 294

Answer 1

Actually this is happening because you are changing the margins of the same view that has the onTouchListener set. To avoid this, you should use separate views - one view should grab the getX() or getY() from its onTouchListener and use that info to change the margins on the other view.

<FrameLayout
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <RelativeLayout
        android:id="@+id/content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"/>
    </RelativeLayout>

    <RelativeLayout
        android:id="@+id/touch_listener"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</FrameLayout>

Answer 2

@I82Much I had this same issue some while ago i also was using the getX() method but instead changed it to getRawX() and it works fine. Hope it helps

Answer 3

Finally figured it out. Problem was I was using event.getX() so I think as I was dragging my finger around it was calculating a value based on the ImageView as well as one based on the underlying surface.