Does a subview viewcontroller added via addSubiew need a dealloc? - iphone

Question

normally when I'm using a viewcontroller that will push the current viewcontroller out of the way, I use a UINavigationController and push/pop the new viewcontrollers and let them handle all the dealloc themselves.
However, for example, in this case, I have a MainViewController, which is the default view when the app starts up. I have a second view, called SecondaryViewController, that is a popup on the main screen (sort of like a lightbox).
Here is the code to illustrate:
//From within mainViewController:
secondaryViewController = [SecondaryViewController alloc] initWithNibName:#"SecondaryViewController" bundle:nil];
[self.view addSubview:secondaryViewController.view];
The secondaryViewController interface looks like this:
//interface
#interface SecondaryViewController : UIViewController
{
IBOutlet UILabel *httpLabel;
IBOutlet UIScrollView *scrollView;
}
#property(retain, nonatomic) IBOutlet UILabel *httpLabel;
#property(retain, nonatomic) IBOutlet UIScrollView *scrollView;
As for the implementation, I have the #synthesize for the #property ivars, but I'm not doing any manual allocs. However, I did put a dealloc method:
- (void)dealloc
{
[httpLabel release];
[scrollView release];
[super dealloc];
}
But I'm not sure I need the above.
So my questions would be the following:
1) Do I need the above dealloc method in this case? Or more generally, when would a subview need a dealloc method?
2) If I do or dont need it, does it depend on whether I'm adding the secondaryViewController via addSubview or pushViewController? For instance, if I wanted to replace the entire mainViewController, with this:
[self.navigationController pushViewController:secondaryViewController animated:NO]
Would the secondaryViewController need a dealloc method?
Thank you!

Answer 1

Yes, you do need the dealloc method exactly as you have it, in this case. You are on the right track because you're assuming that since you are not doing any manual allocating, you don't need to do any dealloc/releasing... however, by specifying the property as (retain, nonatomic), you are doing implicit retaining.
This means that if you ever set those properties, what's actually occurring under the covers is something like this:
-(void)setHttpLabel:(UILabel *)newlabel
{
if (newLabel != httpLabel)
{
[httpLabel release];
httpLabel = [newLabel retain];
}
}
As you can see, your synthesize is causing a retain to occur on an object. If you never balance that retain out with a release, it will leak. So the only logical place to put it, is in your dealloc method. This creates the circle of life.
If you never set these properties and don't have release in dealloc, then it won't leak anything, but you obviously wouldn't want to make those assumptions.
If you didn't have any retain properties or any manual allocing of ivars, then and only then, can you nuke the dealloc method.
Hope that helps.

Answer 2

I think this is allowed in the latest iOS 5+ but previously you were not supposed to add another viewcontrollers view to your main viewcontroller. This is clear misuse and can lead to issues.
The concept of viewcontroller is one who controls all the views. A view controller should not control another viewcontroller unless it is a container viewcontroller such as UINavigationController/UITabBarController.
So please rethink the design. why do you need the SecondaryViewController. Why cannot the mainviewcontroller manage the secondary view as well?
Lastly, every viewcontroller should have the dealloc in it.

Answer 3

If you need to access secondaryViewController from your main view controller after you've added its view to the hierarchy, you should not deallocate it at that point. If you don't need to access the secondary controller after you've displayed it, you can dealloc it at that point.
In practical terms, if secondaryViewController is an ivar, it probably makes sense to keep a retained reference to it. If it's a local variable and you're not accessing it later, you should dealloc it.