view 在父view 拖动不过边界（UIPanGestureRecognizer）

- (void)viewDidPan:(UIPanGestureRecognizer*)sender
{   
   
CGPoint
p = [sender
translationInView:self.superview];

    if(sender.state
==
UIGestureRecognizerStateBegan){

        _initialPoint
=
self.center;

    }

    CGFloat
newCenterX =
_initialPoint.x
+ p.x;

    if
(newCenterX <0) {

        newCenterX =
0;

    }else
if
(newCenterX >
self.superview.bounds.size.width)
{

        newCenterX =
self.superview.bounds.size.width;

    }

   

    CGFloat
newCenterY =
_initialPoint.y
+ p.y;

    if
(newCenterY <
0) {

        newCenterY =
0;

    }else
if
(newCenterY >
self.superview.bounds.size.height)
{

        newCenterY =
self.superview.bounds.size.height;

    }

   

    self.center
=
CGPointMake(newCenterX, newCenterY);

   
}