Assign proper velocity to pan gesture iOS? - ios

Question

I have a tableView with a panGesture. I am able to pan this tableView from bottom part of the screen vertically. However, I want the panGesture to continue with a certain velocity, to get a scrollView kind of effect while panning up/down.
What happens is that the tableView pans very quickly in upwards or downwards direction with no sign of stopping.
Here's what I have done so far :
-(void)handlePanWithVelocity:(UIPanGestureRecognizer *)gestureRecognizer{
CGPoint displacement;
CGPoint velocity = [gestureRecognizer velocityInView:self.mapView];
switch (gestureRecognizer.state) {
case UIGestureRecognizerStateBegan:{
break;
};
case UIGestureRecognizerStateChanged:{
CGPoint translation = [gestureRecognizer translationInView:self.view];
displacement = (isVerticalPan) ? CGPointMake(0, translation.y) : CGPointMake(translation.x, 0);
mytableView.transform = CGAffineTransformMakeTranslation(displacement.x, displacement.y);
break;
};
case UIGestureRecognizerStateEnded: {
displacement.y = displacement.y + velocity.y;
[UIView animateWithDuration:1 animations:^{
mytableView.transform = CGAffineTransformMakeTranslation(displacement.x, displacement.y);
}];
break;
};
case UIGestureRecognizerStatePossible:break;
case UIGestureRecognizerStateCancelled:break;
case UIGestureRecognizerStateFailed:break;
}
}
What can be done to improve the current behaviour?

Answer 1

The thing is that you dont measure the time that it takes to move in the first place. Since velocity it x/t you need to adjust the duration of you UIView animation. You have to measure the time between the Pan Recognizer callbacks and then calculate the speed.
global variables:
double velocity;
NSDate *date;
and then:
-(void)handlePanWithVelocity:(UIPanGestureRecognizer *)gestureRecognizer{
CGPoint displacement;
CGPoint velocity = [gestureRecognizer velocityInView:self.mapView];
switch (gestureRecognizer.state) {
case UIGestureRecognizerStateBegan:{
break;
};
case UIGestureRecognizerStateChanged:{
CGPoint translation = [gestureRecognizer translationInView:self.view];
displacement = (isVerticalPan) ? CGPointMake(0, translation.y) : CGPointMake(translation.x, 0);
mytableView.transform = CGAffineTransformMakeTranslation(displacement.x, displacement.y);
if(date){
double timePassed_ms = [date timeIntervalSinceNow] * -1000.0;
velocity = displacement.y/timePassed_ms;
}
date = [NSDate date];
break;
};
case UIGestureRecognizerStateEnded: {
displacement.y = displacement.y + velocity.y;
[UIView animateWithDuration:1 animations:^{
mytableView.transform = CGAffineTransformMakeTranslation(0, velocity);
}];
break;
};
case UIGestureRecognizerStatePossible:break;
case UIGestureRecognizerStateCancelled:break;
case UIGestureRecognizerStateFailed:break;
}
}
I didnt test the code but you get the general idea.