Interactive UIViewController Transition with new "usingSpringWithDamping:initialSpringVelocity"-animation - objective-c

Question

I try to implement a interactive custom modal UIViewController transition using the new iOS7 APIs. Everything is working as desired as long as I don't use the new
+ (void)animateWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay usingSpringWithDamping:(CGFloat)dampingRatio initialSpringVelocity:(CGFloat)velocity options:(UIViewAnimationOptions)options animations:(void (^)(void))animations completion:(void (^)(BOOL finished))completion
method for animating the transition. It is working fine if I invoke the transition via a button. The problem occurs when the transition is interactive, driven by a GestureRecognzier. If I release my finger the animation is immediately cut of and won't finish. The same code is working if I use
animateWithDuration:delay:options:animations:completion:
instead.
Here is the code which animates the transition:
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
CGRect fullFrame = transitionContext.containerView.frame;
if (!self.dismissal) {
[transitionContext.containerView addSubview:fromViewController.view];
[transitionContext.containerView addSubview:toViewController.view];
fromViewController.view.frame = fullFrame;
toViewController.view.frame = CGRectMake(0, fullFrame.size.height, 0, 0);
[UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:0.5 initialSpringVelocity:0.5 options:UIViewAnimationOptionTransitionNone animations:^{
//animation
toViewController.view.frame = CGRectMake(0,0, fullFrame.size.width, fullFrame.size.height);
} completion:^(BOOL finished) {
[transitionContext completeTransition:![transitionContext transitionWasCancelled]];
}];
} else {
[transitionContext.containerView addSubview:toViewController.view];
[transitionContext.containerView addSubview:fromViewController.view];
fromViewController.view.frame = fullFrame;
[UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0 usingSpringWithDamping:.5 initialSpringVelocity:.5 options:0 animations:^{
fromViewController.view.frame = CGRectMake(0, fullFrame.size.height, fullFrame.size.width, fullFrame.size.height);
} completion:^(BOOL finished) {
[transitionContext completeTransition:![transitionContext transitionWasCancelled]];
}];
//This is working fine
// [UIView animateWithDuration:[self transitionDuration:transitionContext]/2 animations:^{
// fromViewController.view.frame = CGRectMake(0, fullFrame.size.height, fullFrame.size.width, fullFrame.size.height);
// } completion:^(BOOL finished) {
// [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
// }];
}
This is the code behind the gesture recogniser:
#pragma mark - Gesture recognition
- (void)handlePan:(UIScreenEdgePanGestureRecognizer *)pgr
{
CGPoint translation = [pgr translationInView:pgr.view];
CGFloat percentage = fabs(translation.x / CGRectGetWidth(pgr.view.frame));
switch (pgr.state) {
case UIGestureRecognizerStateBegan:
self.interactionInProgress = YES;
[self.respondingVC proceedToNextViewController];
break;
case UIGestureRecognizerStateChanged: {
[self updateInteractiveTransition:percentage];
break;
}
case UIGestureRecognizerStateEnded:
if(percentage < 0.5) {
[self cancelInteractiveTransition];
} else {
[self finishInteractiveTransition];
}
self.interactionInProgress = NO;
break;
case UIGestureRecognizerStateCancelled:
[self cancelInteractiveTransition];
self.interactionInProgress = NO;
default:
break;
}
}

Answer 1

It looks like you're using UIPercentDrivenInteractiveTransition. When you call finishInteractiveTransition, UIPercentDriventInteractiveTransition does not call animateTransition.
You should override both updateInteractiveTransition and finishInteractiveTransition to update your view states.
All my attempts to begin an animation block inside an interactive transition have ended in failure. I finally at least got it to finish the animation by calling [self updateInteractiveTransition:1] in finishInteractiveTransition. Otherwise the views will be left in the state they were in and the transition never completes or the transition is treated as completed but your views are in strange places.