Custom Segue without presentViewController doesn't unwind correctly - ios

Question

I'm implementing a custom segue using controller containment API, e.g.
#implementation CustomSegue
- (void)perform {
UIViewController *sourceViewController = self.sourceViewController;
UIViewController *destinationViewController = self.destinationViewController;
[sourceViewController addChildViewController:destinationViewController];
destinationViewController.view.alpha = 0.0;
[sourceViewController.view addSubview:destinationViewController.view];
[UIView animateWithDuration:0.3 animations:^{
destinationViewController.view.alpha = 1.0;
} completion:^(BOOL finished) {
[destinationViewController didMoveToParentViewController:sourceViewController];
}];
}
#end
View controller hierarchy is trivial: sourceViewController → destinationViewController
When unwinding from the destinationViewController to the sourceViewController, app crashes in [UIStoryboardUnwindSegueTemplate _perform:] with exception Could not find a view controller to execute unwinding for <…>
I did not implement custom -[UIViewController viewControllerForUnwindSegueAction:fromViewController:withSender: or
-[UIViewController canPerformUnwindSegueAction:fromViewController:withSender: which means framework returns correct values (although I implemented it once to check).
When replacing my custom addChildViewController:… code with presentViewController:… in the segue, it works fine: unwinding performs like expected.
The question: is it possible to have a custom segue that creates a custom view controller hierarchy?
Test case project: https://bitbucket.org/zats/unwind/

Answer 1

I think that George Green's comment is relevant, and the way you have your controllers set up is the cause of the crash. I think to do what you want, you should have ZTSFirstViewController added as a child to a custom container controller which will do the unwinding, and the (forward) segue will exchange the children of that custom container controller (switch from ZTSFirstViewController to ZTSSecondViewController). The viewControllerForUnwindSegueAction:fromViewController:withSender: method needs to be implemented in the custom container controller (ViewController in my example). I tested this by adding a container view in IB to ViewController, and changed the class of the embedded controller to ZTSFirstViewController. I added a segue from a button in ZTSFirstViewController to ZTSSecondViewController, and connected the unwind segue from a button in that controller. The unwind: method is in ZTSFirstViewController. The code in the custom segue was this,
- (void)perform {
UIViewController *destinationViewController = self.destinationViewController;
UIViewController *sourceViewController = self.sourceViewController;
if (!self.unwind) {
[sourceViewController.parentViewController addChildViewController:destinationViewController];
destinationViewController.view.alpha = 0.0;
[sourceViewController.parentViewController.view addSubview:destinationViewController.view];
[UIView animateWithDuration:0.3 animations:^{
destinationViewController.view.alpha = 1.0;
} completion:^(BOOL finished) {
[destinationViewController didMoveToParentViewController:sourceViewController.parentViewController];
}];
} else {
[self.sourceViewController willMoveToParentViewController:nil];
[UIView animateWithDuration:0.3 animations:^{
sourceViewController.view.alpha = 0.0;
} completion:^(BOOL finished) {
[sourceViewController.view removeFromSuperview];
[sourceViewController removeFromParentViewController];
}];
}
}
I kept this segue close to your implementation -- it doesn't actually switch the controllers, it just adds the second one as a second child and hides the view of the first.