Hey,
I'm adding a UIViewcontroller as a subview of my current view. With something like that:
[self.view addSubview:viewcontroller.view];
The user can interact with that added viewcontroller so I can't just release it after I added it's view as my subview, right ?
So I would like to release it the dealloc methode and set it to nil in viewDidUnload when my master viewcontroller gets unloaded, right ?
The problem is, the viewcontoller I add as a subview is not added every time. So the question is, how can I ceck if the viewcontroller was added as subview and if so, release it.
Thx a lot !
Sebastian
You can check it like this:
if(viewController)
{
[viewController release];
viewController=nil;
}
and yes u need to put this in your dealloc method.
If you read correctly your code:
[self.view addSubview:viewcontroller.view];
it is not the controller which is being added as a subview, rather the view it manages.
This is an important point, since it means that the controller itself does not get retained. What is retained is the view.
So you can simply go on releasing your viewController in -dealloc as usual:
-(void)dealloc {
[viewController release]; viewController = nil;
...
}
and in your viewController's dealloc you will need to release the managed view, if you allocated it manually (or wherever it makes sense for your controller to release its view, if necessary).
On the other hand, whenever your superview is deallocated, then also the view you added as a subview will be released (as per Apple spec of addSubview behavior). So nothing to worry about here. Just release the viewController properly (and make that the view controller manages correctly tis own view).
One more note: you should not release your view controller in viewDidUnload.
In some open source code that I used to contribute to, we had a macro called RELEASE_TO_NIL which did exactly this.
#define RELEASE_TO_NIL(obj) if(obj != nil) { [obj release]; obj = nil; }
You would use it like this:
RELEASE_TO_NIL(viewController);
Simple as that.
Just add an tag to viewController.view and test if self.view contains that tag.
UIView *testView = [self.view viewWithTag:yourTag];
if(testView!=nil){
doStuff;
}
According to the Apple docs, a UIViewController instance should manage a view that fills the whole screen. If your view does not fill the screen, you could either subclass UIView to handle delegation or make the superview work as a delegate.
Also, the subviews of a view are contained in an instance of NSArray, do [myView subviews] to return this property. Ask the returned array if it contains the subview in question and you can release accordingly.
But, without knowing more, it does sound like you need to rethink how you're setting all this up.
Related
I have created a sample app where i have created some class inherited from NSObject class for defining different atributes and properties of my object . Now i have a subclass a UIView and also able to show that object in my iphone screen.
Now i have a problem whenever i want to delete a triangle i generally call [self removeFromSuperview];and it remove the view from my screen.
But it is just removing the view from screen not completely deleting the object.
How can i delete the object completely?
From what I gather from your description - how about:
[self removeFromSuperview];
[self release];
Does that work? Alternatively, you should put this kind of logic in your view controller. Then, is you have a reference to object (say, myObject), then use:
[myObject removeFromSuperview];
[myObject release];
Removing from the super view does not mean delete this object. Your object can very live without being connected to a UIView hierarchy.
EDIT: (to flesh out Peter Deweese's comment)
When you create an UIView you can do this:
MyView* view = [[MyView alloc] initWithFrame:myViewRect];
[mySuperView addChild:view];
[view release];
This means that you no long own the view, but the super view does. The super view retains your view when its added as a child, and you relinquish it with release. Later, when you do:
[self removeFromSuperview];
The retain count will drop to 0 and your object will be deleted automatically.
Good idea Peter!
I am pretty new to iPhone programming, and was playing around with an app yesterday trying different scenarios with view controllers and nib files. So, I started a new app with a FirstViewController (FVC for short) and an FVC.xib.
I layed out a quick view in FVC.xib and ran the app - view displays, great.
I now wanted to have a second view I could add on top of the main view. So I went ahead and created SecondViewController.xib (SVC) but did not create the .m and .h files. I went about trying to load both these views from the same view controller, and here is where my question lies:
I created a button in FVC.xib and created an IBAction like this:
- (IBAction)loadSVC {
FirstViewController *viewController = [[FirstViewController alloc] initWithNibName:#"SecondViewController" bundle:[NSBundle mainBundle]];
secondView = viewcontroller.view;
[viewController release];
[self.view addSubView:secondView];
}
So this works great and adds the contents of SVC.xib, but when I try and remove that view from the superview, the app crashes:
[secondView removeFromSuperview];
If I actually create a view controller for SVC, use that to instantiate my view in FVC, and move the remove code to the SVC:
[self.view removeFromSuperview];
Everything works. My question - I kind of get why my first method crashes, but I was hoping someone could explain why and what goes on behind the scenes. I'm still a noob with object oriented programming, so what is actually happening in my first case where I create a new instance of FirstViewController and add its view to self.view? Why can't I release it (I assume because the original view is associated with FirstViewController, and when I create a new instance with the second xib it messes everything up) - I'd love a more technical explanation as to what is happening...
Thanks much!!
EDIT to add more info in response to Nick's reply below
Nick - so your answer did clear my thinking a bit in regards to the retain count, etc... I did another test app trying to get this working from a single view controller - think, for example, that I wanted to display an Alert or Welcome message to the user (I know in a real app there are different methods to accomplish this, but this is more of a learning experience) -- so I have my main view # MainViewController and layout my alert message in a xib called alert.xib -- so there is no logic behind the alert message, no reason for it to have a view controller that I can see, my end goal being loading/unloading this on top of my main view from the main view's view controller (or understanding why it is impossible)
I tried this using instance variables as you recommended:
In MainViewController.h:
#import <UIKit/UIKit.h>
UIViewController *secondController;
UIView *secondView;
#interface MainViewController : UIViewController {
}
#property(nonatomic, retain) UIViewController *secondController;
#property(nonatomic, retain) UIView *secondView;
- (IBAction)loadSecond;
- (IBAction)removeSecond;
#end
In MainViewController.m:
#import "MainViewController.h"
#implementation MainViewController
#synthesize secondController, secondView;
- (IBAction)loadSecond {
secondController = [[MainViewController alloc] initWithNibName:#"alert" bundle:[NSBundle mainBundle]];
secondView = secondController.view;
[self.view addSubview:secondView];
}
- (IBAction)removeSecond {
//I've tried a number of things here, like [secondView removeFromSuperview];, [self.secondView removeFromSuperview];, [secondController.view removeFromSuperview];
}
- (void)dealloc {
[secondController release];
[secondView release];
[super dealloc];
}
So - this works to load the alert view, but the removeSecond button does nothing (I did use NSLog to verify the removeSecond method is fired) - why?
Second, and most importantly - is this even possible, or is it horrible practice? Should every nib/view I am manipulating have their own view controller? Am I wrong to think I could just make a new instance of MainViewController and use it to display and remove this no-functionality, very temporary view? (And yes, I realize I could easily create this view programatically or accomplish the end goal in many different ways which would be easier, but I'm trying to really learn this stuff and I think figuring this out will help...
Thanks for the help!
You created a view controller
You accessed its view which caused controller to create the view and call the delegates (i.e. viewDidLoad)
Controller returns the view that you asked for
Now you add the view as a subview which increases its retain count
Controller is released and it releases the view, BUT since view's retain count was increased the view is still there
You try to remove the view, it is unloaded and delegates are to be called (e.g. viewDidUnload), however that messes up since the controller who created the view is released and that piece of memory is... smth else :)
That's why the first method doesn't work.
The second method is NOT correct either but it works because:
You remove controller's view from superview but since controller itself is not released (you didn't call [self release] or anything like that, not saying that you should :), just an example), then the view didn't reach 0 (zero) retain count and is still there - which means its subviews aren't removed
The proper way to do it is to save the reference to the controller as an instance variable (usually declare a synthesized property), and release it only when you are done with the view, making sure that the view is removed from superview before hand. The default templete for a View Based App shows how view controller should be managed
Hope this helps to understand why both methods behave differently
Based on your clarifications, you don't need secondView property or iVar. Also in your loadSecond instead of secontController = bla you need self.secondController = bla, otherwise you simply assign reference to the iVar instead of going through the setter.
Yes, it's possible to load subviews/other resources from a nib without having a dedicated controller
This is how you do it (one of the approaches):
UIView *result = nil;
NSArray *bundle = [[NSBundle mainBundle] loadNibNamed:#"MyNibName" owner:owner options:nil];
for ( id o in bundle ) {
if ( [o isKindOfClass:[UIView class]] ) {
result = (UIView *)o;
break;
}
}
Here the result will contain the first UIView in MyNibName. You can use other criteria to find out whether you got the view you wanted (tags, types...)
How to release view controller created like this:
VCClass *vc = [[VCClass alloc] initWithNibName:#"VCClass" bundle:nil];
[self.view addSubview:vc.view];
so the view appear, UIViewController is allocated. Now I want to releas it from within VCClass. I call inside VCClass:
[self.view removeFromSuperView];
my question is, where should I release "vc" object attached to removed view. Is there a good way to notify viewcontroller that is can be released while view is released ?
addSubview does a +1 to the retain count, and it's usually a good practice to release as soon as you don't need it, and you're handing it to another pointer. It's like a glass ball, it is passed hand by hand, and if no one is holding, it falls to the ground and breaks.
Example:
UIView *sampleView = [[UIView alloc] init]; // Retain count: 1
[self.view addSubview:sampleView]; // Retain count: 2
[self.view release]; // Retain count: 1
When the removeFromSubview: is called, the object will be released:
[sampleView removeFromSuperView]; // Retain count: 0
That's for memory management.
Answering your question, a safer way to do what you want to do (loading just a part of an ViewController from a nib (I'm assuming you're using a nib, because you used #"VCClass" in the initWithNibName:), is to use it as following:
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"VCClass" owner:self options:nil];
UIView *view = (UIView*)[nib objectAtIndex:0];
This works by loading the NibName into memory, and then stealing the first element (if you only have a UIView inside, then it will pick that, as the top-most element). This is done similarly for UITableViewCells when loading them from nib files. Nib Files are autoreleased, and it makes more sense, since you apparently just care about the view itself, not the controller.
After you remove it, add a call to
[self autorelease];
Views don't know about their view controllers except as a weak reference to a delegate. This is to avoid a circular reference, among other reasons. VCs often have a life outside their views - hence, the viewDidLoad and viewDidUnload messages. For example, throughout the lifetime of a tab-bar application, the VCs for each tab might go through many different view instances while never being deallocated. Therefore, you should avoid having the view release its own view controller.
Often, the class that allocated the VC should be the one to release it. In the code you provided, you have:
VCClass *vc = [[VCClass alloc] initWithNibName:#"VCClass" bundle:nil];
[self.view addSubview:vc.view];
The controller class that the above code is in is probably the place best suited to releasing the VC. You might need to devise a delegate call just for this purpose.
[self.view removeFromSuperView]; should release your said view from the memory. Though be warned that this will not be true if your view has been retained by any other object that is its retain count is more than 1. Also look at the second answer on this thread.
Does UIView's removeFromSuperView method remove the UIView from memory
UIPopoverController *historyPop = [[UIPopoverController alloc] initWithContentViewController:nav];
[nav release];
[historyPop setPopoverContentSize:CGSizeMake(400, 500)];
[historyPop presentPopoverFromRect:CGRectMake(button.frame.origin.x, button.frame.origin.y, button.frame.size.width, 5) inView:self.view permittedArrowDirections:UIPopoverArrowDirectionDown animated:YES];
//[historyPop release];
This is my current code, however the Analyser says that the is probably a leak, which there is (as the release line is commented out). But if I uncomment the release line then the app crashes and says dealloc was reach on the popover while it is still visible, so when exactly should I be releasing the popover controller?
As mentioned in several places, the methods that present a popover (either from a rect, or from a toolbar button) do not retain the popover. So, your presenting view controller needs to hold a reference to it and release it at the appropriate time.
You can do this by setting the presenting view controller as the popover's delegate, as mentioned. A simpler, if slightly less memory-efficient, approach is to declare a retain property to hold the UIPopoverController. When you create the popover you assign it to the property, which retains it. If you later create another popover, it will release the previous popover when you reassign the property. Don't forget to release the property in the presenting view controller's dealloc method (as well as viewDidUnload).
This approach won't leak, and you don't need to deal with delegates. But, you will potentially keep a UIPopoverController object around longer than necessary. It's up to you to determine if that's a concern for your app.
Try autoreleasing the popover: [historyPop autorelease]. presentPopoverFromRect does not retain the popover, so autorelease won't work here. You need to setup your class as a delegate of the popover controller, and release the popover in popoverControllerDidDismissPopover:.
I have a UIView in a UIViewController to which I add a custom subview in the viewDidAppear method.
MyView *myView = [[MyView alloc] initWithLabelText:text];
[self.view addSubview:myView];
[myView release];
The text variable is a string used on a label in myView. This text changes every time you come back to the current view. But it seems that viewDidAppear does not reload the view - it rather loads a new view over the old one - so I have two labels over each other.
I tried to use viewWillAppear but it doesn't make any difference. I also tried to use [self.view setNeedsDisplay] - doesn't help. I also tried to make myView an instance variable, but it also didn't help.
What worked was to remove the view explicitly, when I declared it as an instance variable:
- (void)viewDidDisappear:(BOOL)animated
{
[_myView removeFromSuperview];
}
Although there is this workaround I would like to simply reset the view when getting back to it. Does anybody know how to do that? I would appreciate it ;)
Don't alloc and init the custom subview every time, only the first time viewDidAppear is called. Then retain it in a property for subsequent use.
The followings thing can ben considered.
viewDidLoad --> alloc and init your sub views
viewDidAppear --> update sub views
dealloc --> release sub views.