viewWillAppear, viewDidAppear not being called, not firing

 源自：http://www.readmespot.com/question/o/3560669/viewwillappear--viewdidappear-not-being-called--not-firing

 

viewWillAppear, viewDidAppear not being called, not firing

1

(This is both question and answer since it took quite a bit of digging to find the real answer.)

Symptom: viewWillAppear, viewDidAppear were not being called in my UIViewController.

Cause: Embedding a UINavigationController or UITabBarController (my case) in a UIViewController somehow interrupts with the calling of these methods.

Solution: Call them manually in the UIViewController that contains the aforementioned UINavigationController / UITabBarController.

For example (assuming projectNavigationController is your UINavigationController):

-(void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [projectNavigationController viewWillAppear:animated];
}

-(void)viewWillDisappear:(BOOL)animated { 
    [super viewWillDisappear:animated];
    [projectNavigationController viewWillDisappear:animated];
}

-(void)viewDidAppear:(BOOL)animated { 
    [super viewDidAppear:animated];
    [projectNavigationController viewDidAppear:animated];
}

-(void)viewDidDisappear:(BOOL)animated { 
    [super viewDidDisappear:animated];
    [projectNavigationController viewDidDisappear:animated];
}

In my case I had an inner UITabBarController and I called the methods accordingly and all was solved.

(Attribution on the solution: http://davidebenini.it/2009/01/03/viewwillappear-not-being-called-inside-a-uinavigationcontroller/)

Question posted on Stack Overflow by freshfunk

 

Selected Answer

2

I'm going to go ahead and disagree with @St3fan, and use UIKit as the counter-example.

However, the wisdom (or lack thereof), of embedding controllers in general should be guided by sane UI design principles.

The easiest counter-example is UINavigationControllers embedded in UITabBarControllers. These appear all over the place. Just off the top of my head, the iPod app on iPhone, and Contacts within the Phone app on iPhone.

I was curious enough to bother to check what they do with the views (add to the "super-controller" view or to the UIWindow. I was pretty sure I was going to find that the sub-controller views were descendants of the super-controller views in the view hierarchy, which is contrary to St3fan's recommendation.

I whipped up a very quick iPhone app hooking everything up in InterfaceBuilder to create a UITabBarController based app with two tabs, the first of which was a UINavigationController with a plain ole UIViewController as it's root view controller, and a 2nd tab with a plain old UIViewController just so I had a 2nd tab to click later.

Sprinkle in some NSLog statements to output the various UIView's for the controllers we see this:

tabBarController.view = <UILayoutContainerView: 0x5b0dc80; ...
navigationController.view = <UILayoutContainerView: 0x59469a0; ...
rootViewController.view = <UIView: 0x594bb70; ...
Superview: <UIViewControllerWrapperView: 0x594cc90; ...
Superview: <UINavigationTransitionView: 0x594a420; ...
Superview: <UILayoutContainerView: 0x59469a0; ... // navigationController.view
Superview: <UIViewControllerWrapperView: 0x594b430; ...
Superview: <UITransitionView: 0x5b0e110; ...
Superview: <UILayoutContainerView: 0x5b0dc80; ... // tabBarController.view
Superview: <UIWindow: 0x5942a30; ...

The lines prefixed with "Superview" were the output from walking up the rootViewController.view's superview chain until hitting nil.

Then of course a quick glance at the call stack in a couple of places where viewDidDisappear would get called on the root view controller.

First, the call stack when viewDidDisappear is called on the root controller as a result of a new controller being pushed on to the stack:

-[RootController viewDidDisappear:]
-[UINavigationController navigationTransitionView:didEndTransition:fromView:toView:]
...

Second, the call stack when another tab is selected in the top-most UITabBarController:

-[RootController viewDidDisappear:]
-[UINavigationController viewDidDisappear:]
-[UITabBarController transitionFromViewController:toViewController:transition:shouldSetSelected:]

So in all cases, it seems that Apple decided that controllers should be calling the various viewDidAppear, etc methods on their embedded subcontrollers and that the view's should be embedded similarly. I think the OP hit this nail right on the head if we're to take UIKit design as a good lead to follow.

Posted by imaginaryboy

0

Your fix is a workaround for your bad code. You are not supposed to 'embed' view controllers in other view controllers.

If you do, for example if you were writing your own tabbarcontroller-like view controller, then you should add the views of your 'sub-viewcontroller' to the window and not as subviews of the root uiviewcontroller.

If you add them to the window then the system will actually also send your view controller the right callbacks.

Posted by St3fan