tvOS preferredfocusedview is not always called - objective-c

Question

After a viewcontroller has been presented modally, the initial preferredfocusedview is called. However, after we dismiss the viewcontroller and it has been dealloc. preferredfocusedview is not called after presenting the viewcontroller again. Running on tvOS 9.2.
Even adding the following did not help:
-(void) viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
[self setNeedsFocusUpdate];
[self updateFocusIfNeeded];
}
Anyone know what's going on? Or if there's anyways to debug this?
Edit:
the way I am adding the viewcontroller:
viewController = [[UIViewController alloc] init];
[viewController addChildViewController:self];
[viewController.view addSubview:self.view];
[self didMoveToParentViewController:viewController];

Answer 1

If you are using a container view, having multiple ViewControllers or adding only one View Controller, the preferredFocusEnvironments method must be called from the rootView Controller indicating which View Controller to focus.
For eg.
View Controller A has a container View having ViewControllers B and ViewController C inside the Container.
View Controller A should have preferredFocusEnvironments returning which ViewController to focus.
This way, preferredFocusEnvironments on ViewController B or ViewController C will be called whenever the view becomes visible.
If the ViewController A doesn't have preferredFocusEnvironments, then it won't be called on the containerView ViewControllers.

Answer 2

Implementing custom focus behavior in tvOS 9 is disaster. Apple already mentioned that there is a limitation on redirecting focus specially when presenting/ dismissing a viewcontroller in WWDC.
tvOS10 will handle munch better with preferredFocusEnvironments.
https://developer.apple.com/videos/play/wwdc2016/215/
When I needed to fix this focus redirection issues in viewDidAppear in tvOS 9, I had exactly same issues. Sometimes it works, sometimes not. No clue what so ever. But after I put split second delay on setNeedsFocusUpdate / updateFocusIfNeeded in viewDidAppear it was way better in terms of consistency. preferredFocusedView get called all the time.
-(void) viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
[self setNeedsFocusUpdate];
[self updateFocusIfNeeded];
});
}
Do this in both presented and presenting view controllers, if you are manually changing focus. This is all from my observation and I don't think there is a proper way to achieve some focus behavior because tvOS API is kind of new and premature. Sorry about not being able to give you good explanation why this might work. Good luck.