Problem responding to view being popped from navigation controller

Question

I have a detail view controller which is pushed onto the application's navigation controller stack by a given parent controller. The user is able to select table values in the detail controller, which should update the parent controller when, and only when, the detail view is popped and the parent view is made visible again.
Is there a way to do this? I couldn't see any appropriate methods in UIViewController which would be called when the child view is popped. I've tried to make the parent controller conform the UINavigationControllerDelegate protocol and provided an implementation for willShowViewController method, but this method doesn't seem to get called when the view is displayed.
I'm not sure if I'm going about it the right way trying to implement the UINavigationControllerDelegate and there is a bug with my implementation, or there are better ways to go to implement this functionality, such as using a modal controller, etc.

Answer 1

m_userName wrote:
The user is able to select table values in the detail controller, which should update the parent controller when, and only when, the detail view is popped and the parent view is made visible again.
I don't understand why you require the update to be made only when the detail controller is popped, since during the time the detail controller is on top of the stack, the controller underneath isn't visible. It's common practice to pass data to the previous controller any time before the top controller is popped. Note that there's only a short interval between the time the top controller is removed from the stack and the time it's deallocated (unless you've retained that controller elsewhere, which should be avoided for best memory management).
That said, [viewDidDisappear:|http://developer.apple.com/library/ios/documentation/UIKit/R eference/UIViewControllerClass/Reference/Reference.html#//appleref/doc/uid/TP40006926-CH3-SW20] is called during that interval, so I think it would be a good choice for the requirement you described:
- (void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
if (self.navigationController == nil) {
NSLog(@"%s: *POPPED* level=%d", _func_, level);
// pass the data here
The test for a nil navigationController pointer tells us whether the controller is actually off the stack when viewDidDisappear: runs. This is useful in case an instance of this controller class ever pushes another controller on top of it, since viewDidDisappear: will run in that situation as well. But in that case the controller doing the pushing remains on the stack, so its navigationController property won't be nil. If that property is nil when viewDidDisappear: runs, we know self has just been popped.
You can also find the above example in [Problem with text in detailTextLabel of UITableViewCell |http://discussions.apple.com/message.jspa?messageID=12495708#12495708], so if you build the code in that thread you can see how things work together.
- Ray