ios drag and drop subview only working once - objective-c

Question

I have UIView in which I want to be able to drag and drop subviews, and this is working fine once.
- (void)pan: (UIPanGestureRecognizer *)recognizer
{
if (recognizer.state == UIGestureRecognizerStateBegan) {
CGPoint startPos = [recognizer locationInView:self];
for (UIControl *sv in self.subviews){
if ([sv pointInside:startPos withEvent:nil]){
self.controlBeingDragged = sv;
}
}
}
if (((recognizer.state == UIGestureRecognizerStateChanged) ||
(recognizer.state == UIGestureRecognizerStateEnded)) &&
self.controlBeingDragged){
CGPoint translation = [recognizer translationInView:self];
self.controlBeingDragged.center = CGPointMake(self.controlBeingDragged.center.x + translation.x, self.controlBeingDragged.center.y + translation.y);
[recognizer setTranslation:CGPointZero inView:self];
if (recognizer.state == UIGestureRecognizerStateEnded){
self.controlBeingDragged = nil;
}
}
}
However, if I try to drag the same UIControl again, the containing view no longer knows where it is. I can drag it again by starting at the original position, so clearly there is something I am not doing to inform the containing view that its subview has moved. But what?

Answer 1

I'm surprised it's even working once. The pointInside:withEvent: message requires a point in the receiver's coordinate system, but you're sending a point that's in the receiver's superview's coordinate system. You can use convertPoint:toView: for each subview to convert the point to the subview's coordinate system before sending the point in the pointInside:withEvent: message.
CGPoint subviewPoint = [self convertPoint:startPos toView:sv];
if ([sv pointInside:subviewPoint withEvent:nil]) {
...
You might also want to check whether the -[UIView hitTest:withEvent:] message can replace the entire subview-searching loop.