I've created an onTouchListener for dragging Views. Images drag smoothly if I use getRawX()
and getRawY()
. The problem with that is the image will jump to the second pointer when you place a second pointer down then lift the first pointer.
This onTouchListener attempts to fix that issue by keeping track of the pointerId
. The problem with this onTouchListener is while dragging an ImageView, the ImageView jumps around pretty crazily. The getX()
and getY()
values jump around.
I feel like I'm doing this correctly. I don't want to have to write a custom view for this because I've already implemented a scaleGestureDetector and written a custom rotateGestureDetector that work. Everything works fine but I need to fix the issue I get when using getRawX()
and getRawY()
.
Does anybody know what I'm doing wrong here?
Here's my onTouchListener:
final View.OnTouchListener onTouchListener = new View.OnTouchListener()
{
@Override
public boolean onTouch(View v, MotionEvent event)
{
relativeLayoutParams = (RelativeLayout.LayoutParams) v.getLayoutParams();
final int action = event.getAction();
switch (action & MotionEvent.ACTION_MASK)
{
case MotionEvent.ACTION_DOWN:
{
final float x = event.getX();
final float y = event.getY();
// Where the user started the drag
lastX = x;
lastY = y;
activePointerId = event.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE:
{
// Where the user's finger is during the drag
final int pointerIndex = event.findPointerIndex(activePointerId);
final float x = event.getX(pointerIndex);
final float y = event.getY(pointerIndex);
// Calculate change in x and change in y
final float dx = x - lastX;
final float dy = y - lastY;
// Update the margins to move the view
relativeLayoutParams.leftMargin += dx;
relativeLayoutParams.topMargin += dy;
v.setLayoutParams(relativeLayoutParams);
// Save where the user's finger was for the next ACTION_MOVE
lastX = x;
lastY = y;
v.invalidate();
break;
}
case MotionEvent.ACTION_UP:
{
activePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_CANCEL:
{
activePointerId = INVALID_POINTER_ID;
break;
}
case MotionEvent.ACTION_POINTER_UP:
{
// Extract the index of the pointer that left the touch sensor
final int pointerIndex = (action & MotionEvent.ACTION_POINTER_INDEX_MASK) >> MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = event.getPointerId(pointerIndex);
if(pointerId == activePointerId)
{
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
lastX = (int) event.getX(newPointerIndex);
lastY = (int) event.getY(newPointerIndex);
activePointerId = event.getPointerId(newPointerIndex);
}
break;
}
}
return true;
}
};
image1.setOnTouchListener(onTouchListener);
The issue was simple, but unexpected. getRawX/Y()
returns absolute coordinates, while getX/Y()
returns coordinates relative to the view. I would move the view, reset lastX/Y
, and the image wouldn't be in the same spot anymore so when I get new values they'd be off. In this case I only needed where I originally pressed the image (not the case when using `getRawX/Y').
So, the solution was to simply remove the following:
// Save where the user's finger was for the next ACTION_MOVE
lastX = x;
lastY = y;
I hope this will help somebody in the future, because I've seen others with this problem, and they had similar code to me (resetting lastX/Y
)
After a lot of research, I found this to be the issue, getRawX is absolute and getX is relative to view. hence use this to transform one to another
//RawX = getX + View.getX
event.getRawX == event.getX(event.findPointerIndex(ptrID1))+view.getX()
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