Custom UIStoryboardSegue using segueWithIdentifier:source:destination:performHandler: - ios

Question

I am trying to use a custom UIStoryboardSegue to implement a transition between two view controllers. I can do this by subclassing UIStoryboardSegue, and then setting this class in IB. However, I was looking at the docs which say:
If your segue does not need to store additional information or provide anything other than a perform method, consider using the segueWithIdentifier:source:destination:performHandler: method instead.
Implying that you don't need to create the custom subclass, just use the custom performHandler.
I am confused as to where this code should go, and how I go about using it. Do I create the segue as normal in IB and then override that before it is fired (maybe in shouldPerformSegue: or similar). Elsewhere in apple's documentation it says:
Your app never creates segue objects directly; they are always created on your behalf by iOS when a segue is triggered
So I don't quite understand why they are then saying to instantiate a segue using a class creator method.

Answer 1

The point of segueWithIdentifier:source:destination:performHandler:
Provide an alternative to UIViewController performSegueWithIdentifier:sender in cases where you also want to create a custom transition, without creating a segue subclass.
Vend a segue that can be used as the return for segueForUnwindingToViewController:fromViewController:identifier
As noted above, this approach is only viable for segues which you would call manually -- i.e. not for segues that would otherwise be triggered via IB triggers.
So, for example, if you have a segue that needs to be triggered after a certain timeout period (such as a custom lock-screen), you could use segueWithIdentifier:source:destination:performHandler: to handle the custom transition.
-(void)appTimeoutLockScreen
{
UIStoryboardSegue *segue =
[UIStoryboardSegue segueWithIdentifier:#"LockScreenSegue"
source:sourceVC
destination:destinationVC
performHandler:^{
// transition code that would
// normally go in the perform method
}];
// Dev is responsible for calling prepareForSegue and perform.
// Note, the order of calls for an IB triggered segue as well as
// a performSegueWithIdentifier segue is perform first, then
// prepareForSegue:sender. Manual segues need to inverse the call
// in order to ensure VC setup is finished before transition.
[self prepareForSegue:segue sender:self];
[segue perform];
}
Another practical use for the method is unwinding segues. Using a similar scenario
to the previous example, we could use it to return a segue to transition from a lock screen back to the previous viewController:
-(UIStoryboardSegue *)segueForUnwindingToViewController:(UIViewController*)toVC
fromViewController:(UIViewController *)fmVC
identifier:(NSString *)identifier
{
UIStoryboardSegue *segue =
[UIStoryboardSegue segueWithIdentifier:#"FromLockScreenSegue"
source:fmVC
destination:toVC
performHandler:^{
// transition code
}];
return segue;
}