Iphone – How to pop a view from a UINavigationController and replace it with another in one operation

cocoa-touchiphoneuinavigationcontrolleruiviewanimation

I have an application where I need to remove one view from the stack of a UINavigationController and replace it with another. The situation is that the first view creates an editable item and then replaces itself with an editor for the item. When I do the obvious solution within the first view:

MyEditViewController *mevc = [[MYEditViewController alloc] initWithGizmo: gizmo];

[self retain];
[self.navigationController popViewControllerAnimated: NO];
[self.navigationController pushViewController: mevc animated: YES];
[self release];

I get very strange behavior. Usually the editor view will appear, but if I try to use the back button on the nav bar I get extra screens, some blank, and some just screwed up. The title becomes random too. It is like the nav stack is completely hosed.

What would be a better approach to this problem?

Thanks,
Matt

Best Solution

I've discovered you don't need to manually mess with the viewControllers property at all. Basically there are 2 tricky things about this.

  1. self.navigationController will return nil if self is not currently on the navigation controller's stack. So save it to a local variable before you lose access to it.
  2. You must retain (and properly release) self or the object who owns the method you are in will be deallocated, causing strangeness.

Once you do that prep, then just pop and push as normal. This code will instantly replace the top controller with another.

// locally store the navigation controller since
// self.navigationController will be nil once we are popped
UINavigationController *navController = self.navigationController;

// retain ourselves so that the controller will still exist once it's popped off
[[self retain] autorelease];

// Pop this controller and replace with another
[navController popViewControllerAnimated:NO];
[navController pushViewController:someViewController animated:NO];

In that last line if you change the animated to YES, then the new screen will actually animate in and the controller you just popped will animate out. Looks pretty nice!

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