I m Copying my code here below :-
-(IBAction)referencewindow:(id)sender
{
frmReferences *reference = [[frmReferences alloc]initWithNibName:#"frmReferences" bundle:nil];
[self presentModalViewController:reference animated:YES];
}
There are number of places I m using presentModelViewController and my problem is that stack shows memory leakage due to presentmodelviewcontroller.
when we use presentModelViewController to call other nib as above stated then it just override to the previous view but previous view is still in process thats why memory lekage problem is occuring so please tell me when i call other nib file using presentModelViewController then how to unload that previous view from memory while switch to other view and then on other view to next view.
You must release your viewController after call the presentModalViewController method like here:
- (IBAction)referencewindow:(id)sender {
frmReferences *reference = [[frmReferences alloc]initWithNibName:#"frmReferences" bundle:nil];
[self presentModalViewController:reference animated:YES];
[reference release];
}
There is more information here: Modal View Controllers
Your building a navigation hierarchy using present modal view? It could work but you need to released it sometime.
I think if you tried using normal memory management rules it would work out. Try going back from your views and they should be released, you'd see the memory go down in instruments.
Related
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.
Hi I hope somebody can help me with this problem.
I have a UIViewController named "Login" (for example) and when the user has successfully logged in this will call another controller to replace the "Login" controller like below:
[self presentModalViewController:anotherController animated:YES].
I do not need the previous controller any more so I placed a [self release] as shown in the code snippet below.
LoginController.m
- (void)viewDidDisappear:(BOOL)animated {
[self release];
}
This will then call the LoginController's dealloc method and I can be sure it's released.
Now in the new controller that is now in view has a button which calls a UINavigationController like below:
[self presentModalViewController:settingsNavigationController animated:YES];
But this crashes the app which would normally work if I didn't release the previous LoginController.
There is probably an easier or more logical method to release the controller but as I am running out of ideas I sometimes use drastic measures.
Thank you.
You should not be releasing the LoginController, at least not in its own -viewDidDisappear:. That controller is still in use and can be referenced, for example by the navigation controller's parentViewController property. Release the controller when it is no longer part of your view controller hierarchy, not just when it is no longer visible.
In addition [self release] is a warning sign that you are applying incorrect memory management.
1) Replace the "Login" controller
presentModalViewController doesn't replace your login view controller, but it puts anotherController on top of your login view controller.
2) viewDidDisappear
You should read documentation. Quote - You can override this method to perform additional tasks associated with dismissing or hiding the view. If you override this method, you must call super at some point in your implementation.
In other words, you must call [super viewDidDisappear:animated] too.
3) Memory Management
You should definitely need to read Memory Management Guide - http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/MemoryMgmt/MemoryMgmt.html
4) View Controller
You should definitely need to read View Controller Programming Guide too - http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/Introduction/Introduction.html
Two problems with what you are doing.
First, viewDidDisappear is NOT a destructor. Do not release self there. viewDidDisAppear and appear are used for visibility of the view, not in/out of memory.
Second, presentModalViewController is intended for presenting a MODAL view controller, ie child.
You should consider setting up a UINavigationController and calling
[navigationController popToRootViewControllerAnimated:FALSE];
[navigationController pushViewController:(UIViewController*)controller animated:TRUE];
also in some situations you can get away with an [autorelease] view controller using present modal.
I load view controllers all the time in the following format:
-(void)loadSelectUser {
MyViewController *nextController = [[MyViewController alloc] initWithStyle:UITableViewStyleGrouped];
MyAppDelegate *delegate = [[UIApplication sharedApplication] delegate];
[delegate.navigationController pushViewController:nextController animated:YES];
[nextController release];
}
And I've never had an issue with that. But right now I'm dealing with the issue that the next view doesn't load completely. The navigation bar shows up and the viewDidLoad and the numberOfSectionsInTableView methods are both called. That is it. The table doesn't show up, it still shows the previous view.
I imagine this means there is a memory leak or something not connected properly. Is this the right path to be looking? If so, what is your best suggestion for debugging this issue. My code has no error messages so I'm not sure where to start. I load the view properly in a different controller, but for some reason it doesn't do it after this particular view*.
*This view happens to do a lot data manipulation with downloading objects, saving them and such. But again, it looks like it is all working properly. What would mess up the navigation controller loading the next view completely?
Oh, and just to mess things up more, some times, it works properly. But I run it one more time and it doesn't do it again.
Update: TechZen comment about the proper way to push a new view controller seemed to help a little. There is a higher rate of it working, unless I am pushing a tableviewcontroller. Depending on the action my view will push a UITableViewController or a UIViewController with a nib file. The second usually (not always) works.
Also, in a different view I am adding a modal view. But when I try to dismiss it using [self dismissModalViewControllerAnimated:YES]; it doesn't always work. Again it's hit or miss on it. Anyone have an idea of what would be causing the transition of windows to be finicky?
Calling the app delegate to get the navigation controller is unnecessary and risky. Any view controller on a navigation controller stack has a populated navigationController property so you can just use self.navigationController.
It's risky to call the app delegate's navigation controller because you have no guarantee that you will get the same navigation controller as the one that currently holds the view controller calling the push. You could in theory end up with two overlapping and conflict navigation controllers.
Switch the code to self.navigationController and see if that fixes the problem.
i am using UIviewcontroller subclasses. In my main view i have 3 buttons, each button will load a different nib. and each new nib is having one back button to come back to main view.
when i click one the back button of any view to move to the main view the dealloc of that view is not getting called? i didnt understood this.
can anyone explain when those views dealloc will be called?
if the dealloc method hasn't been called, it means that your retained your viewController object by hands. for example, in this case dealloc will not be called after clicking back button to return
MyViewController *controller = [[MyViewController alloc] init];
[self.navigationController pushViewController:controller animated:YES];
You should add
[controller release];
to this code to be sure that your instance of viewController will be deallocated. If you are absolutely sure, that you had sent equal number of alloc(or any message that increases object's retainCount) and release messages for your object and dealloc method doesn't be called anyway, it will be more complex. I hope that this answer will help. If you will find that your situation is "more complex", post a comment, then I'll try to explain with more details.
I too would like to dive deeper into understanding memory management details (below surface level) where it comes to controllers being pushed on and off of the stack. I built my framework from the text, "Beginning iPhone 3 Development" by Mark and LaMarche, but that text effectively re-uses sub-controllers and their dealloc methods never get called.
I have noticed that repeated use of a sub-controller with a NIB containing a UIWebView that calls Google's web directions url ... eventually results in a memory warning and my data is lost. This involves repeated "reuse" of the sub-controller.
If you can point me as well to in depth text that goes into nav controller and sub view memory management, that would be excellent.