UIPanGestureRecognizer get swipe distance in pixels - ios

Question

I'm trying to track the horizontal distance that a user has swiped using a UIPanGestureRecognizer, but I'm having difficulty interpreting the results. Here is the code that I am using:
- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer {
CGPoint startLocation;
if (recognizer.state == UIGestureRecognizerStateBegan) {
startLocation = [recognizer locationInView:self.view];
}
if (recognizer.state == UIGestureRecognizerStateEnded) {
CGPoint stopLocation = [recognizer locationInView:self.view];
CGFloat dx = stopLocation.x - startLocation.x;
NSLog(#"dx: %f", dx);
}
}
If I swipe left-to-right, I get output something like this:
dx: 50328911327402404790403072.000000
My screen is only 320 pixels wide, so my end result cannot be greater than 320. Is there a problem with my code or am I just interpreting this number incorrectly? How can I get this value stated in pixels? Thanks!

Answer 1

startLocation doesn't persist after handlePan: returns, so you're getting garbage.
Either declare startLocation as static or save it in an instance variable / property.

Answer 2

You can use UIPanGestureRecognizer as below:-
CGPoint translatedPoint = [(UIPanGestureRecognizer*)sender translationInView:self.view];
if ([(UIPanGestureRecognizer*)sender state] == UIGestureRecognizerStateBegan) {
firstX = [[sender view] center].x;
firstY = [[sender view] center].y;
}
translatedPoint = CGPointMake(firstX+translatedPoint.x, firstY);
[[sender view] setCenter:translatedPoint];
if ([(UIPanGestureRecognizer*)sender state] == UIGestureRecognizerStateEnded) {
CGFloat velocityX = (0.2*[(UIPanGestureRecognizer*)sender velocityInView:self.view].x);
CGFloat finalX = translatedPoint.x + velocityX;
CGFloat finalY = firstY;