I'm somewhat unclear on the object ownership patterns required for the following instances. When my UIViewController presents a popover controller, an action sheet, or another view controller as modal, am I required to hang onto a retained reference to that child controller until it's been dismissed?
In other words, do the following lines of code effectively "transfer" ownership, or not?
[aPopoverController presentPopoverFromBarButtonItem:someButtonItem permittedArrowDirections:UIPopoverArrowDirectionAny animated:NO];
[anActionSheet showFromBarButtonItem:someButtonItem animated:NO];
[aViewController presentModalViewController:someOtherViewController animated:YES];
Can someone point me to explicit documentation on this subject?
UIPopoverViewController has a slight different memory management/owning. Present a popover does not retain the memory, so you can't transfer the ownership of your popviewcontroller to the presenting object.
To avoid memory leak, you have to adopt the UIPopoverControllerDelegate and implement the DidDismissPopOver method as follow:
- (void)popoverControllerDidDismissPopover:(UIPopoverController *)popoverController {
[popoverController release];
}
This way, you can safe alloc and present a PopOver:
-(void)showSearch:(id)sender {
SearchViewController *searchVC = [[SearchViewController alloc] init];
UIPopoverController *popVC = [[UIPopoverController alloc] initWithContentViewController:searchVC];
popVC.delegate = self;
[popVC setPopoverContentSize:CGSizeMake(320, 100)];
[popVC presentPopoverFromRect:CGRectMake(200, 200, 320, 100) inView:self.view permittedArrowDirections:0 animated:YES];
[searchVC release];
}
Presenting a modal view controller retains the UIViewController. This is actually not clear from the docs. However, I tested it using the following code...
NSLog(#"BEFORE %d", [self.setupViewController retainCount]);
[self.navigationController presentModalViewController:self.setupViewController animated:YES];
NSLog(#"AFTER %d", [self.setupViewController retainCount]);
The self.setupViewController is already retained locally, but presenting it output the following:
2010-05-19 10:07:36.687 LocateMe[27716:207] BEFORE 1
2010-05-19 10:07:36.762 LocateMe[27716:207] AFTER 3
So it is probably being retained in the local modalViewController property, as well as in the view hierarchy. Dismissing it will balance these.
So bottom line is, retain it if you want to control it directly, but you don't have to.
EDIT - Just to be clear, the correct pattern is to always retain an object if you set yourself as its delegate. That's because you should be setting the delegate to nil in your dealloc for safety. Practically though, a modal controller is always going to be dismissed before you dealloc, so it's not an issue. You'll notice Apple also breaks this rule in [UIView setAnimationDelegate:], which actually retains the delegate you set.
Related
Within my mainViewController I'm adding a view from another ViewController. I'm removing it's view when finished. What is the proper way to manage this and where do I release the view controller?
mainVc.m
-(void)showView {
helpPage *elementController = [[helpPage alloc] init];
[self.view addSubview:elementController.view];
}
helpPage.m
-(void)removeView {
[self.view removeFromSuperview];
}
Since you called alloc init on the controller in that instance of mainVc, that instance of mainVc owns releasing the controller.
When it calls addSubView, it will retain the view (and add to view hierarchy) and when it's removed from the superview, it will be released. At that point, when it's release, the controller that created the view is still retaining it as well. When both have released the view, it will go away.
Here's a related SO post:
Does UIView's addSubview really retain the view?
I think you are looking for something like this
mainVc.m
-(void)showView {
helpPage *elementController = [[helpPage alloc] init];
[self.view addSubview:elementController.view];
[elementController release];
}
helpPage.m
-(void)removeView {
[self.view removeFromSuperview];
}
Granted, I haven't seen the rest of your code, so that might not be what you are looking for. However, in terms of memory allocation, any time you alloc something, you must release it later. In the case of views and view controllers, once you add that view or view controller, you can release the copy you "alloc'ed."
I have some view controller which I call with the following method:
myViewController *myView = [[myViewController alloc] initWithNibName:nil bundle:nil];
myView.modalTransitionStyle = UIModalTransitionStyleCoverVertical;
[self presentModalViewController:myView animated:YES];
[myView release];
if I use the app a few times I get a memory warning and the app freezes for a few seconds! I think the reason is that i switch the view but not discharged the old one !!?!!?!!
(i set my outlets to nil and release them)
how can I unload the old view after switching to the new one?
Thanks in advance
When switching the view be sure to call dismissModalViewController:(BOOL)animated on myViewController.
In the class that launch the modalViewController you could make a property for the modal viewcontroller which you retain. Then you could write something like this.
//This would be in an action or something...
if (self.myViewControllerProperty == nil) {
self.myViewControllerProperty = [[[MyViewController alloc] initWithNibName:nil bundle:nil] autorelease];
}
[self presentModalViewController:self.myViewControllerProperty animated:YES];
Then instead of setting the
myView.modalTransitionStyle =
UIModalTransitionStyleCoverVertical;
Move that code to the modalViewController and write self.modalTransitionStyle = UIModalTransitionStyleCoverVertical; I think that looks cleaner, keep the configuration of each viewcontroller separted don't mix it up.
And as the maclema said, call dissmissModalViewController, but you probably are doing that...
Could be any number of problems but you don't need to (and can't) unload the old view. Make sure you are releasing objects and setting outlets to nil in viewDidUnload of all of your view controllers. viewDidUnload will be called when a memory warning occurs so if you don't handle it correctly you'll have leaks and can crash. Other than that, hard to know what else your app is doing that is contributing to the crash.
I have some pretty simple code where I am using a UINavigationController and adding a rootViewController. After some processing has occurred I want to pop off the current view controller and replace it with another one. This seems to work fine, but my original view controller does not dealloc. I set a breakpoint in it's dealloc and it never gets hit. Below is my code. Not sure why happens. Just for testing if I release startController twice it does go away.
StartViewController *startController = [[StartViewController alloc] initWithNibName:#"StartViewController" bundle:[NSBundle mainBundle]];
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:startController];
[nav pushViewController:startController animated:NO];
self.navController = nav;
[startController release];
[nav release];
Thanks any help.
Your ultimate goal is to bring the view controller's retain count to zero. So make sure that everything the view retains is released and anywhere the view is retained also release.
Please check the following possible causes:
Make sure you pop the view controller from the navController if you have a custom back button. The default Back button will work fine.
Make sure that all your IBOutlets are set to nil in viewDidUnload
- (void)viewDidUnload
{
[super viewDidUnload];
self.webView = nil;
}
If your view is an observer to a model class to receive events
For example
model.addObserver(myView);
and sure to also do
model.removeObserver(myView);
I hope this helps.
It looks as though your self.navController has got a holding reference to it. maybe put
self.navController =nil;
somewhere appropriate, so that when the view has been popped it is released.
I was trying to pop off the root view controller. I instead used the setViewControllers message from the UINavigationController object to replace all my view controllers.
MyPlatesViewController* viewController = [[MyPlatesViewController alloc] initWithNibName:#"MyPlates" bundle:nil ];
[self.view addSubview:viewController.view];
then i delete my viewController
[self.view removeFromSuperview];
but leak instrument shows 20 MB memory
What is wrong ?
You leaked the view controller object. After you remove the view from its superview, you need to release the controller as well.
Alternatively, you can do the following:
[self presentModalViewController:viewController animated:NO];
[viewController release];
Then, when dismissModalViewController is called, both the view and the view controller will be released properly.
You called alloc so it's your responsibility to release it. Your code should look like this:
MyPlatesViewController* viewController = [[MyPlatesViewController alloc] initWithNibName:#"MyPlates" bundle:nil ];
[self.view addSubview:viewController.view];
[viewController release]
Note that your controller is retained by the view when you call addSubview and released when you call removeFromSuperview. So with your current code the retain count of viewController is still 1 after calling removeFromSuperview.
Additionally you should review objective-c memory manament here: http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/MemoryMgmt/Articles/mmRules.html
recently I joined two Xcode projects together. To get this thing to work, I had to alloc and initialize my view controller.
self.myViewController = [[MyViewController alloc] init];
But why? In the other project I have the same code. The sole difference is hierarchy of the different views. I added a new view to the top (beginning). So the calling View Controller is not the first view on the stack anymore.
I'm pushing my view in this way on the stack:
[[self navigationController] pushViewController:myViewController animated:YES];
In my NIBs I have added a View Controller object with IB and connected the Outlets.
And I have a memory management question too: If I have a property like myViewController, do I have to release it? The "normal" release is done in the dealloc method. But do I have to use an additional release because of the alloc? I don't think so, but I ask you anyway.
I would need to see more code to answer why you had to alloc your view controller, but I'd say that you always alloc them manually (at least in my experience).
As for the memory management question, if your property is declared as a retain property (#property(retain) UIViewController *myViewController), you are indeed leaking memory, since the retain count after alloc will be 1, and after the retain done by your accessor will be 2. Hence, if you release it only once, you'll end up with a leak.
I usually do this instead:
self.myViewController = [[[MyViewController alloc] init] autorelease];
I found it out: In IB I had to set the nib name on my view controller object. So the alloc and initialization is done by IB?
There is one more option:
(IBAction)loginButton:(UIButton *)sender {
NSLog(#"pressed login");
ICMasterViewController *controller = [[self storyboard] instantiateViewControllerWithIdentifier:#"mainnav"];
[self presentViewController:controller animated:YES completion:nil];
}
On your storyboard you must have UIViewController with name mainnav