If I alloc/init a view and add it to a another view in code (I did not use a xib) - do I need to remove it when the containing UIViewController's dealloc message is sent? I have seen this code in certain places, and wondered is it necessary under some circumstances to free memory?
Thanks,
Marc
If you do this,
UIView *v = [[UIView alloc] init];
[self.view addSubview:v];
[v release];
or
UIView *v = [[[UIView alloc] init] autorelease];
[self.view addSubview:v];
,the v will be released when its parent view release;
When the parent view use addSubview, it will retain the subview, and will release the subview when it is released.
This isn't necessary. All UIView subclasses hold subviews array, which gets released in the final UIView dealloc message, which releases your views.
Related
In my application, I am creating a window and setting a content view. Inspector is showing me some memory leaks.
In setContentView: I think it releases previous NSView.
My code is given below:
//contentrect is NSRect which is already initialized.
//stylemask is NSUInteger which is also initialized.
//window_ is of NSWindow type.
window_ = [NSWindow alloc];
//Here, I am getting memory leak.
window_ = [window_ initWithContentRect:contentrect styleMask:stylemask
backing:NSBackingStoreBuffered defer:NO];
//Set window delegate to receive close notication.
[window_ setDelegate:delegate_];
//I believe this is the behavior is by default.
//[window_ setReleasedWhenClosed:YES];
//Setting the windows title.
[window_ setTitle:title_];
//Setting the window frame screenrect which is also initialized.
[window_ setFrame:screenrect display:YES animate:YES];
//MyView is inherited from NSView.
//Set MyView instead of default NSView.
//Set as it have same content rectangle.
contentrect = [[window_ contentView] frame];
//Allocate MyView.
MyView * view = [[MyView alloc] initWithFrame:contentrect];
[window_ setContentView:view];
[rWindow orderFront:nil];
Edit:
I am not getting memory leak in setContentView which I called, but in setContentView which is called inside as initWithContentRect.
You have to balance retain/release count
you have to release window_ somewhere, one place will be in dealloc
- (void)dealloc
{
[window_ release]; window_ = nil;
// other releases
[super dealloc];
}
it is a bad idea to alloc init in different line
similarly, you have to release your view by add [view release]; after setContentView
or autorelease it
MyView * view = [[[MyView alloc] initWithFrame:contentrect] autorelease];
if you have no idea how management works in Objective-C, you better switch to ARC first and learn details about how it works.
i was reading this code, where setRegions is called after RootViewController is released : i find it a bit strange : does it mean RootViewController is still accessible, even if it was released and self.navigationController "owns" it ?
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// Create the navigation and view controllers
RootViewController *rootViewController = [[RootViewController alloc] initWithStyle:UITableViewStylePlain];
UINavigationController *aNavigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController];
self.navigationController = aNavigationController;
[aNavigationController release];
[rootViewController release];
[rootViewController setRegions:[Region knownRegions]];
// Configure and display the window
[window addSubview:[navigationController view]];
[window makeKeyAndVisible];
}
Thanks
This is bad code.
An object should retain another object for as long as it cares about it. And in this case that rule is broken. The rootViewController is released, and then as you note, a method is called on it. This can be dangerous.
In this case, it works. This is because rootViewController is passed to another object, which retains it. So when we release it, it still has a positive retain count and is not deallocated. So our reference to it still works, and methods called on it work fine.
But lets say some implementation changed and initWithRootViewController: now no longer retained it's argument for some reason (an assumption you can't really make all the time). Suddenly this all crashes because rootViewController gets deallocated.
To fix this funk, you just need to move [rootViewController release]; to after the last useful reference of that object in this function. Your code then becomes more robust and more correct.
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// Create the navigation and view controllers
RootViewController *rootViewController = [[RootViewController alloc] initWithStyle:UITableViewStylePlain];
[rootViewController setRegions:[Region knownRegions]];
UINavigationController *aNavigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController];
self.navigationController = aNavigationController;
// Release temporary objects since we've now sent them to other other objects
// which may or may not retain them (we don't really care which here)
[aNavigationController release];
[rootViewController release];
// Configure and display the window
[window addSubview:[navigationController view]];
[window makeKeyAndVisible];
}
Last thing to note: release and dealloc are very different things. release does not necessarily destroy objects. It simply decrements the retain count by one. And if that retain count ever gets to zero, only then is the object is deallocated. So this code works because a release happens but without triggering a dealloc.
The above is very dangerous code. It might happen to work, but it's just getting lucky. You should never access a variable after you have released it. In fact, it is best practice to immediately set variables to nil after releasing them if they don't immediately go out of scope. Some people only do this in Release mode, and so create a macro like:
#ifdef DEBUG
#define RELEASE(x) [x release];
#else
#define RELEASE(x) [x release]; x = nil;
#endif
The reason for this is to help catch bugs in debug mode (by having a crash rather than just a silent nil pointer), while being a bit safer in release mode.
But in any case, you should never access a variable after you've released it.
RootViewController *rootViewController = [[RootViewController alloc] initWithStyle:UITableViewStylePlain];
(objectA created, retain count is 1, rootViewController points to it)
UINavigationController *aNavigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController];
(objectB created, retain count is 1, aNavigationController points to it)
(objectA retain count is 2 now, both rootViewController and some property in self.aNavigationController point to it)
self.navigationController = aNavigationController;
(objectB retain count is 2 now, both aNavigationController and self.navigationController point to it; assuming self.navigationController is a retain property)
[aNavigationController release];
(objectB retain count is 1 now, however, both aNavigationController and self.navigationController point to it)
[rootViewController release];
(objectA retain count is 1 now, however, both rootViewController and some property in self.aNavigationController point to it)
[rootViewController setRegions:[Region knownRegions]];
(use rootViewController to access objectA)
(This is not good)
Following is my recommended way:
RootViewController *rootViewController = [[[RootViewController alloc] initWithStyle:UITableViewStylePlain] autorelease];
[rootViewController setRegions:[Region knownRegions]];
UINavigationController *aNavigationController = [[[UINavigationController alloc] initWithRootViewController:rootViewController] autorelease];
self.navigationController = aNavigationController;
I dont want to add a sub view, but instead change the "self.view" to another view eg (A warning view) then after the user suppresses the warning I would like to switch back. When ever i try to switch back to the original view i just get a blank screen for reasons i cant understand.
Here is what i currently have in one of my UITableViewControllers
//Show warning view controller
self.warningViewControler = [[[WarningViewController alloc] init] autorelease];
self.view = self.warningViewController.view;
//Then later
self.view = self.tableView; //<< Dosnt work
If you want to change your view, and if the original view is defined/linked into XCode, you must retain it before changing self.view to another view. If not, the original view is released and using it back can cause bad things to happen.
Warning :
self.warningViewControler = [[[WarningViewController alloc] init] autorelease];
self.view = self.warningViewController.view
is a bad bad call. Because you autorelease the controller but you use its view. So you get a view retained with a released controller after some time. Retain the controller and release it yourself when its view is not needed anymore.
Here's the better way to do what I think you're trying to do:
WarningViewController *warningViewController = [[WarningViewController alloc] initWithNibName:#"theRightNiborNil" bundle:nil];
[self presentModalViewController:warningViewController animated:YES];
// or if you don't need to support iOS4 any more:
[self presentViewController:warningViewController animated:YES completion:nil]
// and if you aren't using ARC yet, then [warningViewController release];
Then in your WarningViewController you want some action that calls:
[self dismissModalViewControllerAnimated:YES];
// or again if this is iOS5..
[self dismissModalViewControllerAnimated:YES completion:nil];
Hope that helps.
I've got a UITabBarController which contains a UINavigationController. Within the visible UIViewController, I'm creating a UITableView programatically as follows:
self.voucherTableView = [[UITableView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame] style:UITableViewStylePlain];
self.voucherTableView.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth;
However, the UITabBar is overlapping the UITableView.
When I output the height of the [[UIScreen mainScreen] applicationFrame], it returns 460.00 whereas it should be 367.00.
In Interface Builder, I'm using the 'Simulated Metrics' which automatically sets the height of the view to 367.00.
Is there something I'm missing, no matter what I try I can't see to get the 367.00 height that I need.
As a temp fix, I've set the frame of the UITableView manually, this isn't really ideal so it would be nice to work out why this isn't working:
self.voucherTableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 367) style:UITableViewStylePlain];
You should use self.view.bounds rather than [[UIScreen mainScreen] applicationFrame] as the last one returns you the whole screen frame while self.view.bounds provides you with your view bounds wich seems what you are searching for.
You should add the UINavigationController instance to the UITabBarController and then add a table view controller to the rootViewController property of the UINavigationController instance which should make your life a lot easier.
As a simple example of this, create an empty window-based application (the templates make this a lot more confusing than it really is).
Add your UIViewController/UITableViewController subclasses to the project then use this code as a guide to setting up your project. This code is in your AppDelegate class:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// create our table view controller that will display our store list
StoresViewController *storeListController = [[StoresViewController alloc] init];
// create the navigation controller that will hold our store list and detail view controllers and set the store list as the root view controller
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:storeListController];
[navController.tabBarItem setTitle:#"TableView"];
[navController.tabBarItem setImage:[UIImage imageNamed:#"cart.png"]];
// create our browser view controller
BrowserViewController *webBrowserController = [[BrowserViewController alloc] init];
[webBrowserController.tabBarItem setTitle:#"WebView"];
[webBrowserController.tabBarItem setImage:[UIImage imageNamed:#"web.png"]];
// add our view controllers to an array, which will retain them
NSArray *viewControllers = [NSArray arrayWithObjects:navController, webBrowserController, nil];
// release these since they are now retained
[navController release];
[storeListController release];
[webBrowserController release];
// add our array of controllers to the tab bar controller
UITabBarController *tabBarController = [[UITabBarController alloc] init];
[tabBarController setViewControllers:viewControllers];
// set the tab bar controller as our root view controller
[self.window setRootViewController:tabBarController];
// we can release this now since the window is retaining it
[tabBarController release];
[self.window makeKeyAndVisible];
return YES;
}
In the code sample above the BrowserViewController is a subclass of UIViewController and the StoresViewController class is a subclass of UITableViewController. The UITabBarController and UINavigationController instances are created programmatically and added to the window.
By subclassing the UITableViewController class you avoid having to create a UITableView instance programmatically and get most everything you need out of the box.
When you need to push a detail view onto the UINavigationController instance's stack, you just have use something similar to this:
[self.navigationController pushViewController:YourDetailViewControllerInstance animated:YES];
This will add the detail view UIViewController subclass to the UINavigationController instance's view hierarchy for you and animate the transition.
Lots of controllers in this, but it's totally worth it and will avoid a lot of the problems you're experiencing as this method allows the views to manage resizing and take toolbars/navigation bars into account all by themselves.
I'm trying to create a NSImageView programmatically as a subview of another NSImageView when awakeFromNib is called.
My code is as follows (Fader is defined in MyImageView.h):
#implementation MyImageView
- (void)awakeFromNib {
Fader = [NSImageView initWithFrame: [self frame]];
}
I get the warning message "NSImageView may not respong to +initWithFrame". When I build, the app simply frizzes without showing anything, and I have to "force quit".
What am I doing wrong?
You’ve forgotten to send +alloc in order to allocate the object. Change that line to:
Fader = [[NSImageView alloc] initWithFrame: [self frame]];