Why isn't my segue being performed?

Question

I have a segue that should take place when one of a number of things happen, so it's called programatically, like so:

- (void)unwindAway
{
    NSLog(@"Let's segue");
    [self performSegueWithIdentifier:@"mySegue" sender:self];
    NSLog(@"We should have just performed the segue");
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    NSLog(@"Let's do a segue");
}

but the output I get in the console is:

2014-05-29 22:20:30.173 My App[7848:60b] Let's segue
2014-05-29 22:20:30.178 My App[7848:60b] We should have just performed the segue

so as you can see, it's not even calling prepareForSegue.

The segue name is correct - if I give an invalid segue name it errors as you'd expect.

Any ideas?

Answer 1

对于放松的segue，在视图控制器上调用prepareForSegue:sender: ：，它是segue的源，换句话说就是您要退出的那个。

Answer 2

As per Rob's suggestion in the comments I checked the name of the method in the destination View Controller in the segue. It looked right (and was selected in IB rather than typed) but pasting over it and recompiling fixed the problem. Something must have been messed up in the source code of the storyboard, perhaps an artefact of renaming methods.

It's worth noting if anyone has a similar issue that the app won't generate any error if the destination method of a segue isn't found anywhere (I've confirmed this by typing a nonsense method name).

Answer 3

I know that your issue has been fixed, but for future reference I just want to say that similar problems might be caused by the way the unwind process works (zie the technical note link above).

As soon as the segue has been triggered in a certain view controller, its parent (!) view controller is called with the message: viewControllerForUnwindSegueAction:fromViewController:withSender: . The implementation checks if the parent wants to handle the unwind action. If not, it's array with child view controllers is searched for a view controller that wants to handle the action.

My problem was that the unwind action was implemented in a child view controller of a view controller that was embedded in a navigation controller. So, when te segue began, the navigation controller (the parent) was asked: will you handle the action? It returned NO. Then, it's children were asked the same. It returned NO. Because the message isn't sent to a child view controller of a child of the parent view controller, there isn't a view controller that will handle the unwind action and it is aborted without an error message.

My solution was to implement the unwind action in the view controller itself and not in it's child view controller.