UIViewController viewWillAppear not called when adding as subView - ios

I have a UIViewController that I am loading from inside another view controller and then adding its view to a UIScrollView.
self.statisticsController = [self.storyboard instantiateViewControllerWithIdentifier:#"StatisticsViewController"];
self.statisticsController.match = self.match;
[self.scrollView addSubview:self.statisticsController.view];
I've put breakpoints in the statistics view controller and viewDidLoad is being called but viewWillAppear isn't.
Is it because I'm not pushing it onto the hierarchy or something?

You should add statisticsController as a child view controller of the controller whose view you're adding it to.
self.statisticsController = [self.storyboard instantiateViewControllerWithIdentifier:#"StatisticsViewController"];
self.statisticsController.match = self.match;
[self.scrollView addSubview:self.statisticsController.view];
[self addChildViewController:self.statisticsController];
[self.statisticsController didMoveToParentViewController:self];
I'm not sure this will make viewDidAppear get called, but you can override didMoveToParentViewController: in the child controller, and that will be called, so you can put any code that you would have put in viewDidAppear in there.

I encounter -viewWillAppear: not called problem again. After googling, I came here. I did some tests, and find out that the calling order of -addSubview and -addChildViewController: is important.
Case 1. will trigger -viewWillAppear: of controller, but Case 2, it WON'T call -viewWillAppear:.
Case 1:
controller?.willMoveToParentViewController(self)
// Call addSubview first
self.scrollView.addSubview(controller!.view)
self.addChildViewController(controller!)
controller!.didMoveToParentViewController(self)
Case 2:
controller?.willMoveToParentViewController(self)
// Call adChildViewController first
self.addChildViewController(controller!)
self.scrollView.addSubview(controller!.view)
controller!.didMoveToParentViewController(self)

By default, appearance callbacks are automatically forwarded to children.
It's determined with shouldAutomaticallyForwardAppearanceMethods property. Check value of this propery, if it's NO and if your child viewController should appear right on container's appearance, you should notify child with following methods in container's controller life-cycle implementation:
- (void)viewWillAppear:(BOOL)animated {
[super viewWillAppear:animated];
for (UIViewController *child in self.childViewControllers) {
[child beginAppearanceTransition:YES animated:animated];
}
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
[self.child endAppearanceTransition];
}
- (void)viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
for (UIViewController *child in self.childViewControllers) {
[child beginAppearanceTransition:NO animated:animated];
}
}
- (void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
[self.child endAppearanceTransition];
}
Customizing Appearance and Rotation Callback Behavior
Fixed my problem! Hope it would be helpful.

As mentioned in another answer, the parent view controller might not call viewWillAppear etc. when shouldAutomaticallyForwardAppearanceMethods is set to false. UINavigationController and UITabBarController are known to do that. In this case, you need to call beginAppearanceTransition(_ isAppearing: Bool, animated: Bool) on the child view controller with isAppearing set to true when the view appears and vice versa.
You have to place these calls at appropriate places in your code, normally when you add and remove your child view controller.
Don't forget to call endAppearanceTransition on your child view controller when your custom transition has ended, otherwise viewDidAppear and viewDidDisappear are not called.

Per Apple (https://developer.apple.com/library/content/featuredarticles/ViewControllerPGforiPhoneOS/ImplementingaContainerViewController.html), the correct order of API calls to add a child view controller is:
[self addChildViewController:childVC];
[self.view addSubview:childVC.view];
[childVC didMoveToParentViewController:self];
But I still had the problem where viewWillAppear in the child VC was not sporadically getting called. My issue was that there was a race condition that could cause the code above to get executed before viewDidAppear in the container view controller was called. Ensuring that viewDidAppear had already been called (or deferring the addition of the child VC until it was) solved it for me.

The previous answers are correct, but in case it helps someone - if you override loadView in the child view controller, then none of the other UIViewController methods get called.
Took me some time to realize why my code wasn't running properly, until I realized that I had accidentally overridden loadView instead of viewDidLoad.

Check if your parent VC is a UINavigationViewController (or any other container). In this case the shouldAutomaticallyForwardAppearanceMethods is False and the appearance methods are not called.

I can't understand your questions and your description.
My problem was similar to this only.
CustomTabBarController -> CustomUINavigationController -> RootViewcontroller
viewWillAppear of CustomUINavigationController and RootViewController are not getting called unless you switched to another tab and come back.
The solution is call super.viewWillAppear(animated: true)
override func viewWillAppear(_ animated: Bool) {
**super.viewWillAppear(true)**
}
I struggled for more than a day for this small mistake.

View appearance methods also will not get forwarded if your view controller hasn't loaded its view. This could happen if you override loadView in your child view controller, and the view is already added to the view hierarchy.
In that case, you could do
addChild(childVC)
childVC.loadViewIfNeeded()
childVC.didMove(toParent: self)

Related

viewWillAppear called but viewDidAppear not called after pushViewController

In my app, sometimes pushViewController fails for no reason and what happens is very weird. The navigationBar and navigationItem change but the ViewController is not pushed. Then I can tap nothing on the screen. I find that viewWillAppear is called but viewDidAppear isn't called. I push the home button of iPhone to enter background. After entering foreground again, the ViewController is pushed and viewDidAppear is called. I don't know why and when it happens.
normal viewDidAppear callstack
viewDidAppear after enterBackground callstack
If you can repro by:
Try using the left edge pop gesture when there are no view
controllers below it (i.e on root view controllers, your VC-Home
controller)
Try clicking on any UI elements after this.
Then Disable interactivePopGestureRecognizer when current viewController is the firstVC in navigation controller.
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
self.navigationController.interactivePopGestureRecognizer.enabled = NO;
}
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
self.navigationController.interactivePopGestureRecognizer.enabled = YES;
}
reference:
iOS App Freezes on PushViewController
Is the viewcontroller which you pushed into the view hierarchy overwrite the viewWillAppear/viewDidAppear accidently without calling [super viewWillAppear/viewDidAppear:animated]?
You're probably accidentally calling [super viewDidLoad] inside your viewWillAppear method
For anyone having the same issue as me: Check all your custom views to see if you're not having an infinite loop of layoutSubviews. This is on of the things that happens in between a viewWillAppear and a viewDidAppear.
In my implementation I had a custom Tab bar controller and fore some reason viewDid Appear was empty, putting super calling solved it.
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated) //was missing this line
}
You know,if you overwrite navigationController.interactivePopGestureRecognizer.delegate and not restore it appropriately, this bug will appear,too

Is it necessary to call super in viewWillAppear?

I am trying to understand the scenario of the method calls to view did/will appear and disappear.
What I did is selecting the table cell (higlights in grey) , go to detail view and go back and deselect the selected row (remove the selected cell grey color).
Here are my methods:
-(void)viewDidAppear:(BOOL)animated {
DLog(#"%# did appear", self);
[super viewDidAppear:animated];
if (_isPushed) {
[self.tableView deselectRowAtIndexPath:[self.tableView indexPathForSelectedRow] animated:YES];
_isPushed=NO;
}
}
-(void)viewWillAppear:(BOOL)animated {
DLog(#"%# will appear", self);
[super viewWillAppear:animated]; //If I remove this super call , then it works fine and there is no delay in deselecting the table cell
}
-(void)viewWillDisappear:(BOOL)animated {
DLog(#"%# will disappear", self);
[super viewWillDisappear:animated];
}
-(void)viewDidDisappear:(BOOL)animated {
[super viewDidDisappear:animated];
_isPushed=YES;
}
So , when I put breakpoint the flow goes like this:
without super call:
while pushing to new VC:
current viewWillDisappear //makes sense
new viewWillAppear //makes sense
current viewDidAppear // doesnt make sense , y this should get called as the view is already appeared?
current viewWillDisappear // make sense
current viewDidDisappear //make sense
new viewDidAppear //make sense
while coming back from pushed VC:
current viewWillDisappear
new viewDidDisappear
current viewDidDisappear
new viewDidAppear
with super call:
while pushing to new VC:
current viewWillDisappear
new viewWillAppear
current viewDidAppear
current viewWillDisappear
current viewDidDisappear
new viewDidAppear
while going back from pushed VC:
current viewWillDisappear
new viewDidDisappear
current viewDidDisappear
new viewDidAppear
The flow is pretty much the same either I use super call or not.
But the problem I am facing is, when I use super call in viewWillAppear, there is a delay(around >1second) in deselcting the cell.
If I dont use the super call in viewWillAppear , there is no delay and the cell is deselcting (around <0.5 seconds)
I am not sure to use super call or not.
Can anyone please tell me why there is a delay in deselecting the cell?
Yes, the documentation states you must:
Discussion
This method is called before the receiver's view is about
to be added to a view hierarchy and before any animations are
configured for showing the view. You can override this method to
perform custom tasks associated with displaying the view. For example,
you might use this method to change the orientation or style of the
status bar to coordinate with the orientation or style of the view
being presented. If you override this method, you must call super at
some point in your implementation.
Generally yes, call super. I've seen weird things happen in nav controllers when I forget.
In this case, if you have a UITableViewController, try using its clearsSelectionOnViewWillAppear flag to clear the selection for you.
Yes It's necessary to write super.

UIViewController: detecting when view appears again

I have a UIViewController class that contains a WKWebView and implements WKNavigationDelegate.
I would like to detect when a the view controller appears again. I understand the method loadView but, if I push a new view on the stack and then go back from that view to the previous view (my view controller) which method is called on the view controller?
The method that will be called is viewWillAppear:.
If you push to next view then viewDidLoad will be called first
Then viewWillAppear, viewDidAppear
If you pop to previous screen again (your UIViewController) then
viewWillAppear will be called first and after entire view appears
then viewDidAppear will be called..
viewDidAppear is useful in the cases where any method called at viewWillAppear after that you can Load the data at ViewDidAppear..
The ViewControllers viewDidLoad method is only called once when the view is created for the first time.
// viewDidLoad is called only once when the view is created for the first time
- (void) viewDidLoad
{
[super viewDidLoad];
// do your code here
}
You can also implement the below two methods in side your ViewController.m class
// viewWillAppear is called just before the view is about to be appeared
- (void) viewWillAppear
{
[super viewWillAppear];
// do your code here
}
// is called when the view has appeared
- (void) viewDidAppear
{
[super viewDidAppear];
// do your code here
}

uiview duplicated when switching view controller

I have 2 ViewControllers that I use App delegate to switch them according to user interaction.
in AppDelegate.m I have:
- (void) switchViews
{
if (_viewController.view.superview == nil) {
[_window addSubview:_viewController.view];
[_window bringSubviewToFront:_viewController.view];
[viewController2.view removeFromSuperview];
} else
{
[_window addSubview:_viewController2.view];
[_window bringSubviewToFront:_viewController2.view];
[_viewController.view removeFromSuperview];
}
}
_viewController is for main view and _viewController2 is for glview(I am using isgl3d). The switch works but everytime I switch back to glview, I see duplicated view on top, which I suspect even main view is duplicated too.
Any idea how can I remove the view entirely so that I don't have this issue? Thanks!
You shouldn't be adding and removing the views like this, just change which controller is the root view controller of the window. Doing that make the new controller's view a subview of the window, and removes the old controller's view.
if ([self.window.rootViewController isEqual: _viewController]) {
self.window.rootViewController = viewController2;
}else{
self.window.rootViewController = viewController;
I found out how to do this after watching Stanford Coding Together:IOS.
Some critical info of VC that I am not aware of:
Everytime VC is instantiate, viewDidLoad is called once to setup all the important stuff like outlets and such. Then viewWillAppear and viewWillDisappear will be called for in between view swapping. Because it is called just a moment before view is shown to user, all the geometry setting like view orientation and size is set here.
so what I do is:
I addSubview in viewDidLoad, the do all the running setup in viewWillappear and viewWillDisappear.
one more note: view will remain there as long as the app still running.
anyway Thanks rdelmar for helping.

viewWillAppear not invoked for subview controller

I have an odd case -- a view controller that creates its own view in loadView and which is then added to an existing view.
Here is the code that creates and adds the VC:
self.doneButtonViewController = [[DoneButtonViewController alloc] init];
[self.view addSubview:self.doneButtonViewController.view];
This code is executed in viewDidLoad of the "parent" VC.
The odd thing is that the viewWillAppear method of the added VC is never invoked (nor is viewDidAppear), but the viewWillDisappear method of the added VC is invoked (at the appropriate time), just as one would expect.
Any clue as to why viewWillAppear is not getting invoked?
The application isn't aware of the subview's view controller if you do this, you need to introduce view controller containment to make the root view controller aware. Doing so will handle any events like this.
Because loadView could be called more than once pre iOS 6, I'd advise creating the view controller within init, and then add the subview within loadView. It should be like this:
- (id)init {
...
self.doneButtonViewController = [[DoneButtonViewController alloc] init];
[self addChildViewController:self.doneButtonViewController];
[self.doneButtonViewController didMoveToParentViewController:self];
...
}
- (void)loadView {
...
[self.view addSubview:self.doneButtonViewController.view];
...
}
See "Implementing a Container View Controller" at http://developer.apple.com/library/ios/#documentation/uikit/reference/UIViewController_Class/Reference/Reference.html
As for me, adding child view controller in parent view controller can solve the problem that "viewWillAppear" of the child view controller not get called.

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