hello i'm studying iOS programming
i created a project, which is an empty application
and i created table view controller without xib file.
and i inserted follow code in didFinishLaunchingWithOptions
TableViewController *tvc = [[TableViewController alloc] init];
[self.window addSubView:tvc.view];
[tvc release];
this code was crashed when i scrolled down. why is that?
when i comment this code
[tvc release];
program doesn't crash.
i didn't write dealloc in AppDelegate file.
why is that??
i think i created table view controller with alloc
so retain count is 1.
and add sub view to window and table view controller retain count is 2.
so i release table view controller
but it crash when i scrolled down.
i don't know why..
help me please
Simple, adding tvc.view as a subview of the window causes tvc.view to be retained but does not retain tvc itself. In essence, your TableViewController instance becomes invalid as soon as you call release on it. The app crashes when you scroll presumably because the TableViewController instance is configured as a delegate or datasource for a UITableView or UIScrollView or any other thing associated with tvc.view.
Also note that the way you are displaying the view is not the recommended way to go about it. Really you should be calling presentModalViewController: or pushViewController: and passing the TableViewController instance. This will cause the TableViewController to be retained until it is dismissed/popped, making it safe for you to call release as in your example code.
Or, since you are doing this setup manually as part of didFinishLaunchingWithOptions, you can also set window.rootViewController directly, though again that's not really recommended. XCode allows you to specify the app's default/root view controller and will automatically set it up for you when the app launches.
Actually you have just added the view alone. So the view alone will be retained. The viewcontroller will be released. But the viewcontroller needs to be the datasource and delegate for the tableview. Since it has been deallocated, that datasource will not have any valid reference and so it crashes.
I have been developing iphone applications for around 3months now and theres a few things that stump me and i don't really have an idea how to work round them.
I have a navigation controller controlling the views in my application however every screen that is loaded, used then pushed back loses all the information as it seems to be reinstantiated... I believe this is a possible memory management issue?
But how to i create an app that navigates and retains all information in its views until the application is closed.
Thanks :)
Possible you didn't keep a reference to the view controller, the issue is for UIVIewController not to be released.
Make the view controller an ivar you will instanciate only one time when you push it on stack.
// in .h
MyViewController *mVC;
// in .m
// maybe when the user selects a row in a tableview
if(mVC == nil) {
// first time use, alloc/init
mVC = [[MyViewController ....];
}
// then push on the stack
[self.navigationController ....];
Of course don't forget to release it later.
In this part:
MyViewController *myViewController=[MyViewController alloc] initWithNibName:#"myView" bundle:nil];
[[self navigationController] pushViewController:myViewController animated:YES];
[myViewController release];
You will probably have something like this... Instead, make your myViewController a class's property so you have a reference to it. And drop the [myViewController release]; statement.
Possibly your app is receiving a didReceiveMemoryWarning.
In such cases, when the super class is called, the framework does memory cleaning by unloading all the views that are not currently displayed. This could explain the behavior you are seeing.
To check it further, override didReceiveMemoryWarning in one of your view controllers or applicationDidReceiveMemoryWarning in your app delegate, and put a breakpoint in it. Don't forget to call [super...] appropriately, otherwise pretty soon your app will be killed. What you should see in this way is that the views do not disappear before hitting the breakpoint, and do disappear after that.
If the hypothesis is correct, you should find a way to save the state of your view in viewDidUnload and restore it in viewDidLoad. Look also at didReceiveMemoryWarning reference.
Try to save data in NSUserDefaults it its small or use plist or it its too small like 5-10 objects save in in some variable in appDelegate, and if its too large use sqlite and for saving something like images of files like xml use Document directory
The UINavigationController works like a stack: you push and pop UIViewControllers on it. That means when a UIViewController get popped, it will have its retain count decremented by 1, and if no other object holds a reference to it, it will be deallocated. You can avoid the UIViewControllers getting dealloced by keeping a reference to them yourself by calling -retain on the objects, for instance in your appDelegate.
You can use NSUserDefaults to save the states of the UIControls in the view.
So whenever u r loading a view, set the values to the controls so that it looks like it resume from the place where we left.
I'm writing my own SplitViewController from scratch (i.e. by subclassing UIViewController and not UISplitViewController).
It has two sub-viewControllers (one for the left panel and one for the detail right panel), to which I need to send the appropriate messages (viewWillAppear, viewDidAppear, viewWillDisapppear and viewDidDisappear).
I am already forwarding those messages when my custom SplitViewController receives them and it works fine. However I am struggling to figure out when to send them when any of the two sub-viewcontrollers is replaced by a new one, which also needs to receive those messages. I am adding the view of the new UIViewController properly but the messages are not called adequately.
My initial approach was to call them in the setter of the sub-viewControllers, calling viewWillDisappear to UIViewController about to be released and viewWillAppear to the new UIViewController set, but this one is executed before viewDidLoad and therefore I presume is wrong.
I have also seen that UIView has a method didAddSubview: that might be useful to know when to call viewDidAppear on the correspondent UIViewController.
Any help would be much appreciated!
If you want to mirror UISplitViewController, it seems best to just have dummy UIViewControllers that print out whenever each method is called.
As for your current problem of the ordering of viewWillDisappear, viewWillAppear and viewDidLoad, just do:
-(void)setSomeViewController(UIViewController newVC)
{
[oldVC viewWillDisappear];
[newVC view]; // Causes newVC to load the view,
// and will automatically call -viewDidLoad
[newVC viewWillAppear];
[oldVC.view removeFromSuperview];
[self.view addSubview:newVC.view];
//retain and release as appropriate
// other stuff you'll need to mirror, etc. etc.
}
I am using UINavigationController to move between views. When I move back and forth in views, the memory used by my app keeps on increasing. On placing NSLog statements in the dealloc method of all viewcontrollers, I noticed it was being called for only some viewcontrollers and not all that were popped.
For instance, this is the sequence in which views are pushed MainViewController -> viewcontroller1 -> viewcontroller2 -> viewcontroller3
Now in viewcontroller3 if I do a popToViewController:mainController, dealloc is called only for viewcontroller3. It is not called for viewcontroller1 and 2.
Can someone please tell me why this is happening.
Found the problem. The dealloc method was not being called if any of the references held by a viewcontroller were still in memory. In my case it was the MPMoviePlayerController object which was not released in viewcontroller1 and viewcontroller2.
It is a case of last on, first off. So if you imagine your first view controller is the bottom bun of a burger, you then add the burger (second view controller) and then the top burger (third view controller).
If you go back to the burger you take off the top bun (popViewController: calls the dealloc method of the view that is popped). If you want to go back to the bottom bun then you have to pop the burger (dealloc is called every time the view is popped).
not sure why on pop to root the second view controller's dealloc wouldn't be called though..
hmm
where you navigate your controllers there should be need to write this line after pushviewcontroller,
[viewControllername release];
then it would be call each viewcontroller Dealloc method :)
You should also keep in mind that dealloc is not always guaranteed to run.
use like [self.navigationController popToRootViewControllerAnimated:YES];
It worked for me... calls all dealloc methos of my 10 view controllers
I've read numerous posts about people having problems with viewWillAppear when you do not create your view hierarchy just right. My problem is I can't figure out what that means.
If I create a RootViewController and call addSubView on that controller, I would expect the added view(s) to be wired up for viewWillAppear events.
Does anyone have an example of a complex programmatic view hierarchy that successfully receives viewWillAppear events at every level?
Apple's Docs state:
Warning: If the view belonging to a view controller is added to a view hierarchy directly, the view controller will not receive this message. If you insert or add a view to the view hierarchy, and it has a view controller, you should send the associated view controller this message directly. Failing to send the view controller this message will prevent any associated animation from being displayed.
The problem is that they don't describe how to do this. What does "directly" mean? How do you "indirectly" add a view?
I am fairly new to Cocoa and iPhone so it would be nice if there were useful examples from Apple besides the basic Hello World crap.
If you use a navigation controller and set its delegate, then the view{Will,Did}{Appear,Disappear} methods are not invoked.
You need to use the navigation controller delegate methods instead:
navigationController:willShowViewController:animated:
navigationController:didShowViewController:animated:
I've run into this same problem. Just send a viewWillAppear message to your view controller before you add it as a subview. (There is one BOOL parameter which tells the view controller if it's being animated to appear or not.)
[myViewController viewWillAppear:NO];
Look at RootViewController.m in the Metronome example.
(I actually found Apple's example projects great. There's a LOT more than HelloWorld ;)
I finally found a solution for this THAT WORKS!
UINavigationControllerDelegate
I think the gist of it is to set your nav control's delegate to the viewcontroller it is in, and implement UINavigationControllerDelegate and it's two methods. Brilliant! I'm so excited i finally found a solution!
Thanks iOS 13.
ViewWillDisappear, ViewDidDisappear, ViewWillAppear and
ViewDidAppear won't get called on a presenting view controller on
iOS 13 which uses a new modal presentation that doesn't cover the
whole screen.
Credits are going to Arek Holko. He really saved my day.
I just had the same issue. In my application I have 2 navigation controllers and pushing the same view controller in each of them worked in one case and not in the other. I mean that when pushing the exact same view controller in the first UINavigationController, viewWillAppear was called but not when pushed in the second navigation controller.
Then I came across this post UINavigationController should call viewWillAppear/viewWillDisappear methods
And realized that my second navigation controller did redefine viewWillAppear. Screening the code showed that I was not calling
[super viewWillAppear:animated];
I added it and it worked !
The documentation says:
If you override this method, you must call super at some point in your implementation.
I've been using a navigation controller. When I want to either descend to another level of data or show my custom view I use the following:
[self.navigationController pushViewController:<view> animated:<BOOL>];
When I do this, I do get the viewWillAppear function to fire. I suppose this qualifies as "indirect" because I'm not calling the actual addSubView method myself. I don't know if this is 100% applicable to your application since I can't tell if you're using a navigation controller, but maybe it will provide a clue.
Firstly, the tab bar should be at the root level, ie, added to the window, as stated in the Apple documentation. This is key for correct behavior.
Secondly, you can use UITabBarDelegate / UINavigationBarDelegate to forward the notifications on manually, but I found that to get the whole hierarchy of view calls to work correctly, all I had to do was manually call
[tabBarController viewWillAppear:NO];
[tabBarController viewDidAppear:NO];
and
[navBarController viewWillAppear:NO];
[navBarController viewDidAppear:NO];
.. just ONCE before setting up the view controllers on the respective controller (right after allocation). From then on, it correctly called these methods on its child view controllers.
My hierarchy is like this:
window
UITabBarController (subclass of)
UIViewController (subclass of) // <-- manually calls [navController viewWill/DidAppear
UINavigationController (subclass of)
UIViewController (subclass of) // <-- still receives viewWill/Did..etc all the way down from a tab switch at the top of the chain without needing to use ANY delegate methods
Just calling the mentioned methods on the tab/nav controller the first time ensured that ALL the events were forwarded correctly. It stopped me needing to call them manually from the UINavigationBarDelegate / UITabBarControllerDelegate methods.
Sidenote:
Curiously, when it didn't work, the private method
- (void)transitionFromViewController:(UIViewController*)aFromViewController toViewController:(UIViewController*)aToViewController
.. which you can see from the callstack on a working implementation, usually calls the viewWill/Did.. methods but didn't until I performed the above (even though it was called).
I think it is VERY important that the UITabBarController is at window level though and the documents seem to back this up.
Hope that was clear(ish), happy to answer further questions.
As no answer is accepted and people (like I did) land here I give my variation. Though I am not sure that was the original problem. When the navigation controller is added as a subview to a another view you must call the viewWillAppear/Dissappear etc. methods yourself like this:
- (void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[subNavCntlr viewWillAppear:animated];
}
- (void) viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[subNavCntlr viewWillDisappear:animated];
}
Just to make the example complete. This code appears in my ViewController where I created and added the the navigation controller into a view that I placed on the view.
- (void)viewDidLoad {
// This is the root View Controller
rootTable *rootTableController = [[rootTable alloc]
initWithStyle:UITableViewStyleGrouped];
subNavCntlr = [[UINavigationController alloc]
initWithRootViewController:rootTableController];
[rootTableController release];
subNavCntlr.view.frame = subNavContainer.bounds;
[subNavContainer addSubview:subNavCntlr.view];
[super viewDidLoad];
}
the .h looks like this
#interface navTestViewController : UIViewController <UINavigationControllerDelegate> {
IBOutlet UIView *subNavContainer;
UINavigationController *subNavCntlr;
}
#end
In the nib file I have the view and below this view I have a label a image and the container (another view) where i put the controller in. Here is how it looks. I had to scramble some things as this was work for a client.
Views are added "directly" by calling [view addSubview:subview].
Views are added "indirectly" by methods such as tab bars or nav bars that swap subviews.
Any time you call [view addSubview:subviewController.view], you should then call [subviewController viewWillAppear:NO] (or YES as your case may be).
I had this problem when I implemented my own custom root-view management system for a subscreen in a game. Manually adding the call to viewWillAppear cured my problem.
Correct way to do this is using UIViewController containment api.
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
UIViewController *viewController = ...;
[self addChildViewController:viewController];
[self.view addSubview:viewController.view];
[viewController didMoveToParentViewController:self];
}
I use this code for push and pop view controllers:
push:
[self.navigationController pushViewController:detaiViewController animated:YES];
[detailNewsViewController viewWillAppear:YES];
pop:
[[self.navigationController popViewControllerAnimated:YES] viewWillAppear:YES];
.. and it works fine for me.
A very common mistake is as follows.
You have one view, UIView* a, and another one, UIView* b.
You add b to a as a subview.
If you try to call viewWillAppear in b, it will never be fired, because it is a subview of a
iOS 13 bit my app in the butt here. If you've noticed behavior change as of iOS 13 just set the following before you push it:
yourVC.modalPresentationStyle = UIModalPresentationFullScreen;
You may also need to set it in your .storyboard in the Attributes inspector (set Presentation to Full Screen).
This will make your app behave as it did in prior versions of iOS.
I'm not 100% sure on this, but I think that adding a view to the view hierarchy directly means calling -addSubview: on the view controller's view (e.g., [viewController.view addSubview:anotherViewController.view]) instead of pushing a new view controller onto the navigation controller's stack.
I think that adding a subview doesn't necessarily mean that the view will appear, so there is not an automatic call to the class's method that it will
I think what they mean "directly" is by hooking things up just the same way as the xcode "Navigation Application" template does, which sets the UINavigationController as the sole subview of the application's UIWindow.
Using that template is the only way I've been able to get the Will/Did/Appear/Disappear methods called on the object ViewControllers upon push/pops of those controllers in the UINavigationController. None of the other solutions in the answers here worked for me, including implementing them in the RootController and passing them through to the (child) NavigationController. Those functions (will/did/appear/disappear) were only called in my RootController upon showing/hiding the top-level VCs, my "login" and navigationVCs, not the sub-VCs in the navigation controller, so I had no opportunity to "pass them through" to the Nav VC.
I ended up using the UINavigationController's delegate functionality to look for the particular transitions that required follow-up functionality in my app, and that works, but it requires a bit more work in order to get both the disappear and appear functionality "simulated".
Also it's a matter of principle to get it to work after banging my head against this problem for hours today. Any working code snippets using a custom RootController and a child navigation VC would be much appreciated.
In case this helps anyone. I had a similar problem where my ViewWillAppear is not firing on a UITableViewController. After a lot of playing around, I realized that the problem was that the UINavigationController that is controlling my UITableView is not on the root view. Once I fix that, it is now working like a champ.
I just had this problem myself and it took me 3 full hours (2 of which googling) to fix it.
What turned out to help was to simply delete the app from the device/simulator, clean and then run again.
Hope that helps
[self.navigationController setDelegate:self];
Set the delegate to the root view controller.
In my case problem was with custom transition animation.
When set modalPresentationStyle = .custom viewWillAppear not called
in custom transition animation class need call methods:
beginAppearanceTransition and endAppearanceTransition
For Swift. First create the protocol to call what you wanted to call in viewWillAppear
protocol MyViewWillAppearProtocol{func myViewWillAppear()}
Second, create the class
class ForceUpdateOnViewAppear: NSObject, UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool){
if let updatedCntllr: MyViewWillAppearProtocol = viewController as? MyViewWillAppearProtocol{
updatedCntllr.myViewWillAppear()
}
}
}
Third, make the instance of ForceUpdateOnViewAppear to be the member of the appropriate class that have the access to the Navigation Controller and exists as long as Navigation controller exists. It may be for example the root view controller of the navigation controller or the class that creates or present it. Then assign the instance of ForceUpdateOnViewAppear to the Navigation Controller delegate property as early as possible.
In my case that was just a weird bug on the ios 12.1 emulator. Disappeared after launching on real device.
I have created a class that solves this problem.
Just set it as a delegate of your navigation controller, and implement simple one or two methods in your view controller - that will get called when the view is about to be shown or has been shown via NavigationController
Here's the GIST showing the code
ViewWillAppear is an override method of UIViewController class so adding a subView will not call viewWillAppear, but when you present, push , pop, show , setFront Or popToRootViewController from a viewController then viewWillAppear for presented viewController will get called.
My issue was that viewWillAppear was not called when unwinding from a segue. The answer was to put a call to viewWillAppear(true) in the unwind segue in the View Controller that you segueing back to
#IBAction func unwind(for unwindSegue: UIStoryboardSegue, ViewController subsequentVC: Any) {
viewWillAppear(true)
}
I'm not sure this is the same problem that I solved.
In some occasions, method doesn't executed with normal way such as "[self methodOne]".
Try
- (void)viewWillAppear:(BOOL)animated
{
[self performSelector:#selector(methodOne)
withObject:nil afterDelay:0];
}
You should only have 1 UIViewController active at any time. Any subviews you want to manipulate should be exactly that - subVIEWS - i.e. UIView.
I use a simlple technique for managing my view hierarchy and have yet to run into a problem since I started doing things this way. There are 2 key points:
a single UIViewController should be used to manage "a screen's worth"
of your app
use UINavigationController for changing views
What do I mean by "a screen's worth"? It's a bit vague on purpose, but generally it's a feature or section of your app. If you've got a few screens with the same background image but different overlays/popups etc., that should be 1 view controller and several child views. You should never find yourself working with 2 view controllers. Note you can still instantiate a UIView in one view controller and add it as a subview of another view controller if you want certain areas of the screen to be shown in multiple view controllers.
As for UINavigationController - this is your best friend! Turn off the navigation bar and specify NO for animated, and you have an excellent way of switching screens on demand. You can push and pop view controllers if they're in a hierarchy, or you can prepare an array of view controllers (including an array containing a single VC) and set it to be the view stack using setViewControllers. This gives you total freedom to change VC's, while gaining all the advantages of working within Apple's expected model and getting all events etc. fired properly.
Here's what I do every time when I start an app:
start from a window-based app
add a UINavigationController as the window's rootViewController
add whatever I want my first UIViewController to be as the rootViewController of the nav
controller
(note starting from window-based is just a personal preference - I like to construct things myself so I know exactly how they are built. It should work fine with view-based template)
All events fire correctly and basically life is good. You can then spend all your time writing the important bits of your app and not messing about trying to manually hack view hierarchies into shape.