I am working with Automatic Reference Counting.
I have a custom UIViewController subclass and whenever I call -presentViewController: animated:completion: or remove its view from the superview I would like to NSLog something like "I am dealloced" so I know that the view controller has successfully been removed. I have implemented the -dealloc method in my view controller. However I started a test project where I just had two UIViewController instances (no retain cycles) and -dealloc is not called either when I push the second UIViewController modally or when I remove the superview or when I remove it from the parent view controller. Am I missing something ? In my original project (not the test case) Instruments shows me that those controllers leave a memory footprint that I can't get rid off.
If you want to switch view controllers, and have the one you're switching away from be deallocated, then just switch the root view controller of the window. So, if you're in VC1 and want to go to VC2, then do this in VC1:
VC2 *vc2 = [[VC2 alloc] init]; // or however else is appropriate to get an instance of this class
self.view.window.rootViewController = vc2;
If you haven't created any property to point to vc1, then it will be deallocated after making this switch.
If you want to use a modal presentation or a modal segue (to get the animation when you switch controllers), you can still get the initial controller to be deallocated by switching the root view controller after the presentation from the viewDidAppear method of vc2:
-(void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
self.view.window.rootViewController = self;
}
To get a print when the View Controller is deallocated you can implement the dealloc method as
- (void) dealloc {
NSLog(#"The instance of MyViewController was deallocated");
}
Then to get a print when the View Controller left the view you can implement
- (void) viewWillDisappear:(BOOL)animated {
[super viewWillDisappear:animated];
NSLog(#"The instance of MyViewController left the main view")
}
If you use -presentViewController:animated:completion: you are retaining the parentViewController every time you call this method. ModalViewControllers are simply pushed on top of the other ViewController.
ModalViewControllers are only designed for some kind of information / User Input and stuff like that. If you want to dealloc the ParentViewController you have to deal with your own implementation.
dealloc method isn't called when the class is retained (or something in this class is retained) and not reeleased. It is justly for projects with both ARC and without it. So check your code twice.
Related
I'm developing an application which will work based on maps. So once user opens MapViewController then I will load some data every 5 seconds.
I'm using navigation controller(Push view controller).
So every time when user goes to MapViewController viewdidload method calling. I don't want like that.
That's why I'm trying to avoid viewdidload method like tabbarcontroller.
Is there any way to achieve this?
viewDidLoad is getting called because your MapViewController is getting deallocated when you pop it off of the top of your navigation controller. When you recreate the view controller, it's getting allocated all over again, and the view loads again. If you keep a reference to MapViewController in the class containing your navigation controller, then ARC will not deallocate the object, and you can use this reference to push it back onto the stack so viewDidLoad will not get called again.
Edit: Adding code for reference:
MapViewContoller *mapViewController; // declared globally so there's a strong reference.
- (void) openMapViewController {
if (!mapViewController) {
mapViewController = [self.storyboard instantiateViewControllerWithIdentifier: MapViewControllerID];
}
[self.navigationController pushViewController: mapViewController, animated: YES];
}
Try this
-(void)clickForPush{
// declarre viewcontroller e.g 'saveRecipeVC' instance globally in interface
if (!saveRecipeVC) {
saveRecipeVC = [self.storyboard instantiateViewControllerWithIdentifier:SaveRecipeVCID];
}
[self.navigationController pushViewController:saveRecipeVC animated:YES];
}
viewDidLoad is intended to use when,not possible or efficient to configure 100% of an interface in a XIB. Sometimes, a particular property you wish to set on a view isn't available in a XIB. Sometimes, you use auto layout, and you realize that the editor for that is actually worse than writing auto layout code. Sometimes, you need to modify an image before you set it as the background of a button.
If you dont want to do these things make your viewDidLoad empty. Than avoiding. Or
Add code conditionaly into your viewDidLoad.
(void)viewDidLoad {
[super viewDidLoad];
if(condition) {
// put your code here
}
}
I'm experiencing a memory leak (the UINavigationController and its root View Controller are both being leaked) when presenting and dismissing a UINavigationController in a subview. My method of presentation of the navigation controller seems a bit non-standard, so I was hoping someone in the SO community might be able to help.
1. Presentation
The Navigation Controller is presented as follows:
-(void) presentSubNavigationControllerWithRootViewControllerIdentifier:(NSString *)rootViewControllerIdentifier inStoryboardWithName:(NSString *)storyboardName {
// grab the root view controller from a storyboard
UIStoryboard * storyboard = [UIStoryboard storyboardWithName:storyboardName bundle:nil];
UIViewController * rootViewController = [storyboard instantiateViewControllerWithIdentifier:rootViewControllerIdentifier];
// instantiate the navigation controller
UINavigationController * nc = [[UINavigationController alloc] initWithRootViewController:rootViewController];
// perform some layout configuration that should be inconsequential to memory management (right?)
[nc setNavigationBarHidden:YES];
[nc setEdgesForExtendedLayout:UIRectEdgeLeft | UIRectEdgeRight | UIRectEdgeBottom];
nc.view.frame = _navControllerParentView.bounds;
// install the navigation controller (_navControllerParentView is a persisted IBOutlet)
[_navControllerParentView addSubview:nc.view];
// strong reference for easy access
[self setSubNavigationController:nc];
}
At this point, my expectation is that the only "owner" of the navigation controller is the parent view controller (in this case, self). However, when dismissing the navigation controller as shown below, it is not deallocated (and as a result its rootViewController is also leaked, and so on down the ownership tree).
2. Dismissal
Dismissal is pretty simple, but it seems not to be sufficient for proper memory management:
-(void) dismissSubNavigationController {
// prevent an orphan view from remaining in the view hierarchy
[_subNavigationController.view removeFromSuperview];
// release our reference to the navigation controller
[self setSubNavigationController:nil];
}
Surely something else is "retaining" the navigation controller as it is not deallocated. I don't think it could possibly be the root view controller retaining it, could it?
Some research has suggested that retainCount is meaningless, but FWIW I've determined that it remains at 2 after dismissal, where I would expect it to be zero.
Is there an entirely different / better method of presenting the subNavigationController? Maybe defining the navigation controller in the storyboard would have greater benefit than simply eliminating the need for a few lines of code?
It is best practice when adding a controller's view as a subview of another controller's view, that you make that added view's controller a child view controller; that is, the controller whose view your adding it to, should implement the custom container controller api. An easy way to set this up is to use a container view in the storyboard which gives you an embedded controller automatically (you can select that controller and, in the edit menu, choose embed in Navigation controller to get the UI you're trying to make). Normally, this embedded view controller would be added right after the parent controller's view is loaded, but you can suppress that by implementing shouldPerformSegueWithIdentifier:sender:. I created a simple test app with this storyboard,
The code in ViewController to suppress the initial presentation, and the button methods to subsequently present and dismiss it is below,
#implementation ViewController
-(BOOL)shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender {
if ([identifier isEqualToString:#"Embed"]) { // The embed segue in IB was given this identifier. This method is not called when calling performSegueWithIdentifier:sender: in code (as in the button method below)
return NO;
}else{
return YES;
}
}
- (IBAction)showEmbed:(UIButton *)sender {
[self performSegueWithIdentifier:#"Embed" sender:self];
}
- (IBAction)dismissEmbed:(UIButton *)sender {
[[self.childViewControllers.firstObject view] removeFromSuperview];
[self.childViewControllers.firstObject willMoveToParentViewController:nil];
[self.childViewControllers.firstObject removeFromParentViewController];
}
#end
The navigation controller and any of its child view controllers are properly deallocated when the Dismiss button is touched.
The navigationController property on a UIViewController is retain/strong, which is presumably the other strong reference.
So try popping all view controllers from the navigation controller and see if that works.
This is puzzling me.
The context
The original tutorial I'm following.
Where the segue is added to the Main View via a custom segue:
- (void) perform {
MainViewController *source = (MainViewController *)self.sourceViewController;
UIViewController *destination = (UIViewController *) self.destinationViewController;
for(UIView *view in source.main.subviews){
[view removeFromSuperview];
}
source.currentViewController = destination;
destination.view.frame = CGRectMake(0, 0, source.main.frame.size.width, source.main.frame.size.height);
[source.main addSubview:destination.view];
}
The TextField is connected as delegate in the child View Controller. All things being equal I get the app crashed without any message.
The workaround
In the Main View Controller, in -(void)prepareForSegue: I've added [segue.destinationViewController setDelegate:self]; in the meantime I've added a property in the child View Controller id<UITextFieldDelegate> delegate and modified the textfield delegate as self.delegate.
This works, but the trouble is that I've to set the delegated methods in Main View Controller which is not quite efficient as I have more View Controllers to add.
The Objective
How do I set each View Controller to be the delegate for itself without crashing?
The immediate cause of your error is that the view controller that your views belong to is being deallocated. The fact that your views are on screen while their view controller is deallocated highlights a fundamental flaw in the approach of taking views off one view controller and adding them to another. View controller containment is the correct way to solve an issue like this.
Changing the currentViewController property to strong will fix the memory management issue you're seeing, but it's just a bandaid. Your currentViewController will still be missing rotation methods, appearance and disappearance methods, layout methods, and so forth. View controller containment ensures these methods get called for the view controller whose views are on screen.
Here is an altered version of your project that illustrates how to use view controller containment. I think that will be a better solution than manually removing and adding subviews of the view controllers themselves. See the Apple docs for more info on custom view controller containers.
At first, let's see crash report. Please, do the following:
1. Add Exception Breakpoint
2. Edit it as in the picture
You should create a custom class for the destinationViewController wich will implement UITextFieldDelegate
#interface DestinationViewController <UITextFieldDelegate>
#end
And from storyboard add the class to UIViewController that has TextField
And make the connections for elements and TextField delegate.
Implement delegate methods.
You will not need the implementation of prepareForSegue: anymore. You will have two different classes with different elements. Only if you need to pass something from source to destination then you use prepareForSegue:
Hope you'll understand
I have this view controller (class1) , which has a UICollectionView in it .
When i am finish with this view, i am going to the next view, but i can see that the memory consumption of this view(class1) is not cleared and being added to the next view (class2).
Both view controllers are made with storyboard, and has a name , and when i finish with view1 (class1) i am going to the next one with :
//in view1 i do when exit
UIViewController *mainV=[self.storyboard instantiateViewControllerWithIdentifier:#"MainView"];
mainV.modalTransitionStyle = UIModalTransitionStyleCrossDissolve;
[self presentViewController:mainV animated:YES completion:^(void)
{
[self.myCache removeAllObjects];//NSCache
[self.GridView removeFromSuperview]; //collection view
[self.view removeFromSuperview];
}];
Seems that memory is still not freed.
Is there another way to move to next view and just clear everything before ?
In that code class1 is presenting class2. But class1 is still there, presenting class2, until it does a "dismissViewController:" method.
If you want to go back to mainView from class1. And in the case of class1 being presented by mainView. Then mainView have to do a dismissViewController:
In other case you are stacking a pile of view controllers, one presenting the next one.
The pattern most used in objetive-c is to send a message from class1 to its presenter. A delegation pattern. The presenter then dismiss the viewController.
Even after grid view is removed from superview, it won't be cleared from memory if it's an iVar of your view controller class or a strong property. Try setting GridView to nil after you call [self.GridView removeFromSuperview].
viewController's view is not loaded just after that viewController is pushed into navigation controller.
This is my code snippet.
- (void)myMethodInClassA {
// window's root view controller is navigation controller
UINavigationController *naviCtrl = (UINavigationController*)[UIApplication sharedApplication].keyWindow.rootViewController;
MyViewController *myVC = [[MyViewController alloc] initWithNibName:#"MyViewController" bundle:nil];
[naviCtrl pushViewController:myVC animated:NO];
// at this point, myVC's view is NOT loaded
}
When I call myMethodInClassA, myVC's viewDidLoad is called AFTER that method returns. I'd expected that myVC's view is loaded just after navigation controller's pushViewController:animated: is called and before myMethodInClassA returns.
When exactly view controller's view is loaded? Apple's documentation just says it is loaded when it is first accessed. It's a bit ambiguous. why doesn't navigation controller's pushViewController: access view controller's view?
p.s. sorry for initial ambiguous question.
Pushing a view controller (VC) onto a navigation controller's stack makes the VC into a child view controller of the navigation controller (which is a container view controller). Creating such a child-parent relationship is a distinct step which does not cause the child VC's view to be loaded immediately. Rather the container VC loads the view at a later time. I believe there is no explicit specification for what "later" means - usually it will be when the container VC has decided that the time has come to integrate the child VC's view into the container VC's view hierarchy. But basically it simply happens at the discretion of the container VC's implementation.
That being said, anyone can force a VC's view to be loaded by simply accessing the VC's view property. For instance, in your code you could add this line
myVC.view;
which would trigger loadView and then viewDidLoad in MyViewController.
However, in your case if MyViewController needs to react to the event that it has been associated with a container VC, then it would be better to override one (or both?) of the following methods in MyViewController:
- (void) willMoveToParentViewController:(UIViewController*)parent
{
// write your code here
}
- (void) didMoveToParentViewController:(UIViewController*)parent
{
// write your code here
}
You need to be aware, though, that willMoveToParentViewController and didMoveToParentViewController are also invoked when MyViewController is popped from its parent navigation controller's stack. You can detect that this is the case by checking the parent argument for nil.
(Swift 2)
Since this question doesn't have an accepted answer...
What I ended up doing is create a convenience init at the child view controller:
convenience init() {
self.init(nibName: "ChildViewController", bundle: nil)
//initializing the view Controller form specified NIB file
}
and in the parentViewController's viewDidLoad():
let commentsView = CommentsViewController()
self.addChildViewController(commentsView)
self.momentsScrollView.addSubview(commentsView.view)
commentsView.didMoveToParentViewController(self)
As stated above,viewDidLoad gets called once when a view is pushed,you might want to do your stuff in viewWillAppear or viewDidAppear.
Ya if that ViewController will be already pushed in navigationController stack then ViewDidLoad method will not be called again.
First time when you will push that ViewController then viewDidLoad will be called.
So if you need that your some functionality is to be executed every time then implement it in viewWillAppear method because it will be called every-time you push your viewController.
Hope it helps you.
are you pushing the view controller for the first tym?if YES then only viewDidLoad() of the controller will be called and if its already pushed and this is not the first tyn then viewWillAppear () will be called.(or) if you are making a new instance every tym u push it then viewDidLoad() will be called.
I find that I have to call loadViewIfNeeded()
https://developer.apple.com/documentation/uikit/uiviewcontroller/1621446-loadviewifneeded