This is driving me crazy.
I am under the impression that awakeFromNib Method is called only once(even when that view is visited again), correct me if i am wrong.
I have an app with 3 views.
The last one being the subclass of a UIview where i draw using drawRect.
I had a working code with the method awakeFromNib in the last view, with the method being called only once how many ever times i visit the view.
Now i deploy the app to my device and update my Xcode to version 4.
When i run the code again and debug, the method awakeFromNib is called everytime the view is visited.
I dont think update would do such a crazy thing, but i am thoroughly confused.
Is there some kind of a memory leak or am i missing something?
Thank you
I am under the impression that awakeFromNib Method is called only once(even when that view is visited again), correct me if i am wrong.
-awakeFromNib will be called on each instance of a class whenever an instance of that class is loaded from a nib file. You should be able to expect it to only be called once on a particular instance but should handle it being called many times on different instances of any given class.
UIViewControllers will unload their views when they receive a memory warning and their view is not visible. The view will be reloaded the next time the view controller's 'view' property is called. You should understand and support this behavior to minimize your app's memory use as it allows you to only keep the currently visible views in memory at any given time.
It sounds like you are not expecting that controller's view to be unloaded and reloaded from your nib.
Related
I have what seems like a weird (non?) issue with UIViewController. It appears that the controller is not releasing its subviews when it is dealloc'd. I placed NSLog messages in all of the subview's dealloc method as well as the view controller. The view controller dealloc gets called but the subview's do not. However, if I then push another instance of that view controller on to the navigation stack, it appears that all of the subviews of the previous instance are then released (I get a bunch of NSLog messages in the console letting me know). I've check and I have no separate reference to the custom view controller in the presenting view controller (the one that's doing the pushing).
One small (maybe) detail: The custom view controller does receive a block it stores and then executes before popping. However, I did send nil to it and I get the same behavior. Plus, the presenting view controller does dealloc when popped of the stack, so no retain cycle.
Also, I did try explicitly releasing each view in the dealloc method of the custom view controller. Same behavior.
Is it possible the navigation controller would be holding on to it? It doesn't seem to do this to any of my other view controllers.
My problem is that this does represent a memory leak (of all those subviews); though the leak doesn't stack, it's still a leak.
Ok, this is embarrassing. I did find the problem in another class (called ViewDef) I was inadvertently using as a collection class. It was a quick and dirty way of keeping track of my subviews when I was first figuring out some animations (months ago). ViewDef stored frame/font/color/etc info retrieved from a database, so it was convenient to also store the views when figuring out animations (between orientations). These ViewDefs were being store by my model and passed around, so of course the views were also being retained (and replaced later by another view controller). Anyway, I forgot to insert a warning in my code to fix this later.
Moral of the story: If you plan on doing something stupid, at least document your stupidity so you don't have to broadcast it over the internet later.
you could try setting the subviews to nil in the viewDidUnload method maybe that will help
One thing to try is to make sure all your subviews delegates are set to nil.
Please let me know at what times init and loadView method gets called.
To my knowledge init method gets called only once when view is initialized and loadView is called anytime view is loaded. So, even if you are pushing a new view in the view stack and then popping it then also the loadView of the poped up view should get called. But when I am running my code in debugging mode, both of these methods are getting called once, irrespective of how many times I am loading the same screen. Please let me know if I am missing something.
you are right at some points :)
The init method is being called when the ViewController object is instantiated. The loadView method gets called every time a ViewController should load its view into memory. This can happen before the view is displayed for the first time OR when it should be displayed for a second, third,... time but had been removed from memory before. (this might happen if your app runs out of memory.)
If you want to execute some code every time the view becomes visible, you should have a look at the methods viewWillAppear/viewWillDisappear/viewDidAppear/viewDidDisappear.
loadView is called when you access the view property of your view controller and it's nil.
If the view has been unloaded (viewDidUnload has been called for memory purpose) then loadView will be called again. If not it will not be called.
What you want is viewWillAppear: or viewDidAppear:.
I'm developing an app to browse online photos, and sometimes received memory warning(level 1), after that, if I go back to last UIViewController(in a NavigationControll), I found that some custom UIView lost, I cannot get them back, but I can create new such UIView
does anyone know the problem?
The memory warning prompts the os to dump any unneeded views. If you create them in IB, or in the viewDidLoad or loadView method in your view controller they'll be re-created when your view re-loads. You could also have your view controller retain them specifically, but that'll have a larger memory footprint than just re-creating them whenever they're needed.
I should say, loadView is only called if you don't use a nib for creating your view, so viewDidLoad is probably where you want to put them.
It's expected behavior. You can override didReceiveMemoryWarning (i.e. do nothing and don't call on super); but what you really want is to handle those situations correctly, i.e. set the views up again if necessary.
I put an NSlog in my dealloc method of my view controller. It does not get consistently called. I do notice that ViewWillDisappear does get called always. Would it be ok to move all my tidy upcode here? Setting stuff to Nil and release calls.
Anybody got some advice on why dealloc is not getting called? I know it says in docs it may not get called, but if you have a very simple App it gets called always. So something i do must be affecting the dealloc.
This is the code that calls my ViewController than isnt always calling my dealloc.
-(IBAction) playComputerTapped:(id)sender
{
PlayGameViewController *pgvc = [[PlayGameViewController alloc]
initWithNibName:#"PlayGameViewController" bundle:[NSBundle mainBundle]];
pgvc.gameMode = 1;
[self presentModalViewController:pgvc animated:YES];
[pgvc release];
}
The above code takes me from the mailmenu ViewController into the game.
Below is the code to leave the gameViewController and take me back to the menu.
[self.parentViewController dismissModalViewControllerAnimated:YES];
Thanks
-Code
Don't you mean viewDidUnload instead of viewWillDisappear ?
viewWillDisappear is called when the view controller is disappearing. This usually happens when the view controller is being popped out, or other view controller is pushed to the stack. Purpose of viewWillDisappear is to stop active actions - for example stop animations, hide some elements or similar.
viewDidUnload is probably what you meant as this one is called when view controller's view is unloaded. This should never happen for a view controller that is currently visible, only for controllers that are somewhere in the navigation stack (part of UITabBarController or UINavigationController), but not currently visible. Purpose of viewDidUnload is to release any UI elements that are part of the view and that the view controller retained as well.
To understand it's important to realize the reasons why a view for such controller would want to be unloaded. Reason is memory consumption. Views consume considerable amount of memory, even when they are not currently visible. Views are usually very easy to reconstruct - simply by calling the code that constructed them in the first place. That's especially very easy if you are using Interface Builder. So these views are best candidates to be freed to gain more memory.
When system doesn't have enough memory it starts calling didReceiveMemoryWarning method of view controllers which are not currently visible. If you have created your controllers from template in Xcode, this method simply calls super's (UIViewControllers's) implementation [super didReceiveMemoryWarning]. That default implementation will release self.view, which in turn should deallocate it together with all its subviews.
Now let's say that your view-controller needs access to some of the subviews to manipulate it in some way. For example you can have a UILabel element there and you want to change its content accordingly. To access this element you create a member variable (IBOutlet) and connect it to the element. Now your view-controller owns that label, so its retain-count is increased. When controller's view is released, so is the label, but because your view-controller still retains the label, it will not be deallocated. Therefore you should release the label in viewDidUnload method.
I've seen applications that were creating views programmatically (in loadView method), but loading was done in such dirty way that it was not possible to reconstruct the view after it was once deallocated. Therefore each time system was out of memory, it had called didReceiveMemoryWarning which in turn deallocated the view, but after navigating back to that view-controller application had crashed. A fast "bugfix" was to remove calling [super didReceiveMemoryWarning] in view-controllers. Well, system didn't get the memory and some strange effects occurred, but at least the application didn't crash immediately.
Now the third one - dealloc. This is called when object is not owned by anyone and its memory is going to be freed. Here you need to release all objects that you have retained. For view-controllers those are usually references to model classes.
I want to describe one more possible scenario. Let's say you have a view-controller displaying a chat with another person. Let's say it's very fancy chat, with emoticons and buddy-icons being animated. Let's say that each chat-entry is displayed as a cell of UITableView.
When your buddy sends you a message, you want to append a new cell into table-view by reloading it. Therefore your view-controller has an outlet to the table-view.
In viewWillDisappear you should stop the animations of emoticons and icons.
In viewDidUnload you should release the table-view.
In dealloc you want to release chat's history (probably NSArray of all messages sent and received during this conversation).
Now if you navigate away from your chat, viewWillDisappear gets called and you stop the animations.
When system is low on memory, and your view-controller is not visible, didReceiveMemoryWarning gets called and the view is released. Your viewDidUnload gets called and you release UITableView so that it can be really deallocated.
When you navigate back to the chat, loadView gets called again and your view is constructed again, viewDidLoad is called after that. Your model (representation of chat conversation) is still there, so the table-view's datasource has all the data as before, so table-view will display exactly the same thing as before the view was deallocated. After all viewWill/DidAppear is called where you start the animations.
When you finish chatting with your friend, you release the view controller, and it gets deallocated - dealloc is called, you release an array containing the chat messages, and cleanup everything else.
I hope it make things a little clearer.
Well that depends.
If you need to reduce the memory footprint of your app, unloading stuff while the view is not visible via viewWillDisappear is a good way to go. However you'll need to re-initalize everything once the view will be shown again, depending on its content this may produce considerable overhead - maybe even without the need.
For a small app (in terms of memory usage), using dealloc to unload your stuff is fine. It will be called only if the objects retain count drops to zero and is the last method that will be run before the object is destroyed. When using autorelease, that may not be the case right away and of course the object could be retained by some object other than the parentviewcontroller, preventing it from being destroyed and thus dealloc from being called.
You might want to check out the Memory Management Programming Guide, it'll explain things more detailed.
I'm playing around with the iPad SplitView template and it was working fine before I started swapping out view objects in my RootViewController. When it was working fine, the application:didFinishLaunchingWithOptions method would be called and would setup my persistant store objects, then the RootViewController:viewDidLoad method would be called to populate my rootView with data from my store. I opened up IB and started swapping out view objects in my RootView and now the application:didFinishLaunchingWithOptions method never gets called, but the RootViewController:viewDidLoad method still does. Obviously, the app crashes because the viewDidLoad method depends on the successful execution of the didFinishLauchingWIthOptions method to setup the persistent store objects. Does anyone have any thoughts on what is causing this or how I can go about investigating what's causing this?
I'm obviously new to iPhone OS development, so I apologize if this questions is absurd in any way. Thanks so much in advance for your help!
This is propabaly caused by the fact that in MainWindow.xib, your application delegate object is not connected to File's Owner (UIApplication). You can open the MainWindow.xib and right click on your App Delegate to see if it has a connection in Referencing Outlet to File's Owner. If not, set it to. And this will fix your problem.
-viewDidLoad is not called from -application:didFinishLaunchingWithOptions:. They are independent. The call hierarchy could be summarized as:
load app; call -application:didFinishLaunchingWithOptions:
window is visible, load views of view controllers.
call -viewDidLoad.