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Question

Inside of navigationController , when I'm in a ChildViewController and when the user taps on Back Button. I would love to send some data to the parentViewController before I go away.

Is any simple why to do this besides using

-(void)viewWillDisappear;

First, because this ChildViewController also has its own child, and when it gets pushed, viewWillDisappear gets called as well.

Second, when I user hits home button. it get called.(I guess)

Please, any reasonable and proper way to do this?

Answer 1

Here's a nice simple solution, that gets around the issue that viewWillDisappear is called when modalViewControllers are shown, or further viewControllers are pushed. Eg detects the case where we're actually taken off the stack.

-(void)viewWillDisappear:(BOOL)animated {
  NSUInteger ind = [[self.navigationController viewControllers] indexOfObject:self];
  if (ind == NSNotFound) {
      // do something, we're coming off the stack.
  }
}

The advantage of this is that you don't need to subclass UINavigationController.

Source: http://objectivesea.tumblr.com/post/21705735018/poppingoffthestack

Answer 2

I would solve this problem using the UINavigationControllerDelegate .

In this case, you can use it to keep track of your controllers and you can implement navigationController:willShowViewController:animated: to transfer the data you need between the controllers. It's a lot cleaner than trying to hook into the viewWillDisappear notification, because you can isolate the data transfer logic within that delegate instead of having pieces of it in every controller.

Answer 3

You can do this in any of following ways:

1. Send a notification when the second controller is going away and have the parent listen for it.

2. Create a delegate protocol that lets the second controller reference a parent method directly.

3. Use the parent's viewWillAppear: and check the isMovingToParentViewController property for whether it's just re-appearing.

and apply what is best for your value passing conditions and availability of values.