iOS: different addSubview behavior between iOS 4.3 and 5.0

Question

while coding in iOS 4.3 before, I found while add a view controller's view to another view with [superview addSubView:controller.view], the controller instance will not receive the -viewWillAppear/viewDidAppear message, than I found same issue in some thread in stack overflow. After that, I manually call -viewWillAppear/-viewDidAppear as needed.

but, after upgrade to iOS 5.0, some frisky UIView behavior happened. Finally I found that in iOS 5, the [superview addSubView:controller.view] , will send a -viewWillAppear/-viewDidAppear message to the controller instance automatically, plus my manually calls, there are two duplicated message each time the controller action its behavior.

and I also found a similar issue: iOS 5 : -viewWillAppear is not called after dismissing the modal in iPad

Now, the problem is, after search apple's documents, I didn't find any explicitly doc for diff about these issues. I even wonder if this is a guaranteed view life cycle behavior in iOS 5.0 .

Does anyone fix similar issues or find some guidelines about these difference. cause I want to run my app both in 4.x & 5.x iOS.

Answer 1

In iOS 4 you had to manually call -viewWillAppear, -viewWillDisappear, etc. when adding or removing a view from your view hierarchy. These are called automatically in iOS 5 if the view is being added or removed from the window hierarchy. Fortunately, iOS 5 has a method in UIViewController that you can override to revert the behaviour back to how it worked with iOS 4. Just add this to your UIViewController:

-(BOOL)automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers {
   return NO;
}

This is probably the easiest solution as long as you're supporting both iOS 4 and iOS 5. Once you drop support for iOS 4 you might consider modifying your code to use the newer approach when swapping views.

Edit 5 February 2012

Apparently this function requires the child view controller be added to the main view controller using the addChildViewController: method. This method doesn't exist in iOS4, so you need to do something like this:

  if ([self respondsToSelector:@selector(addChildViewController:)] ) {
     [self addChildViewController:childViewController];
  }

Thanks to everyone who corrected me on this.

Answer 2

This may not be an answer what you want, but I had same kind of problem.

In my case, when I added a view controller's view to another view controller's view as a subview, the subview was received viewWillAppear only in iOS 5.0 not iOS 4.X.

So I added a nasty condition.

[self.view addSubview:self.viewController.view];
if ([[[UIDevice currentDevice] systemVersion] compare:@"5.0"] == NSOrderedAscending) {
    [self.viewController viewWillAppear:animated];
}

From iOS 5.0, Apple provides a way to implement custom container view controllers like UINavigationController or UITabController. I think this change affects when viewWillAppear is called.

This problem may be solvable if we use -[UIViewController addChildViewController:].

Answer 3

The answers above a slightly incomplete. Let's presume you have 2 view controllers, ControllerA, and ControllerB.

ControllerA.view is already added to the window(it is the parent), and you want to add ControllerB.view as a subview of ControllerA.

If you do not add ControllerB as a child of ControllerA first, the automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers will be ignored, and you will still be called by iOS5, meaning that you'll call your view controller callbacks twice.

Example in ControllerA:

- (BOOL)automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers {
    return NO;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.controllerB = [[ControllerB alloc] initWithNibName:@"ControllerB" bundle:nil];

    [self.view addSubview:self.controllerB.view];
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.controllerB viewWillAppear:animated];
}

In ControllerB NSLogging in viewWillAppear:

- (void)viewWillAppear:(BOOL)animated
{
    NSLog("@ControllerB will appear");
}

This will result in iOS5 only displaying that NSLog message twice. i.e. You're automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers has been ignored.

In order to fix this, you need to add controllerB as a child of controller a.

Back in ControllerA's class:

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.controllerB = [[ControllerB alloc] initWithNibName:@"ControllerB" bundle:nil];
    if ([self respondsToSelector:@selector(addChildViewController:)])
        [self addChildViewController:self.controllerB];

    [self.view addSubview:self.controllerB.view];
}

This will now work as expected in both iOS4 and iOS5 without resorting to the horrible hack of checking iOS version strings, but instead checking on if the function we're after is available.

Hope this helps.

Answer 4

It is iOS5 behavior:
viewWillAppear, viewDidAppear, ... are executed automatically after addSubView: for iOS5.
So for iOS5 no need to execute manually those methods as need for iOS<5.0.

The fix may be:

if ([[UIDevice currentDevice].systemVersion doubleValue] < 5.0) {
...execute viewWillAppear or other
}