iOS中插座的内存管理

Question

Hi I have this in my application : The question is, should I put self.label =nil ; in viewDidUnload ? If yes, why?

//.h
@interface MyClass

@property (nonatomic, retain) IBOutlet UILabel *label;

@end

//.m
@implementation Myclass

@syntesize label = label_;

- (void)dealloc
{
   self.label =nil;
}

@end

Answer 1

Yes, you should set the label property to nil both in viewDidUnload and in dealloc . viewDidUnload is called in low memory situations which enables the app to purge unneeded memory.

Not setting it to nil in viewDidUnload will not usually cause a memory leak in, but it will prevent the app from saving memory when needed.

Answer 2

You should do.

viewDidUnload is called in low memory condition. So if you want to clean up call self.yourOutlet = nil also in this method. Furthermore it allows you to save extra memory for your app.

The next time (after viewDidUnload method is called) your view will be loaded into memory again ( viewDidLoad will be called) and your outlet will be set up correctly.

As a rule of thumb any IBOutlet s you release in dealloc , should also be released (reference set to nil like self.label = nil ) in this method.

A note

You should not call self.label = nil; in dealloc . Instead do [label_ release]; as documented in Apple Memory Management Guide .

In addition, Stack Overflow search is your friend:

When is UIViewController viewDidUnload called?

When should I release objects in -(void)viewDidUnload rather than in -dealloc?

Hope that helps.

Edit

if you not use ARC (I think not) you should call also [super dealloc]; like the following:

- (void)dealloc
{
   [label_ release];

   [super dealloc];
}

Answer 3

You should. Although not necessary in most cases, it is considered good practice to set all your pointers to objects to nil on viewDidUnload. Paul Hegarty explains that on CS193P lecture number 8, Controller Lifecycle.

You can watch it here: http://itunes.apple.com/itunes-u/ipad-iphone-application-development/id473757255?mt=2

Answer 4

You can put this, but you can also put [label release], self.label = nil; or just [label release];

It's memory management so that the memory reserved for that object be garbage collected [memory released]. Very important on old iphone 3g, because it has less memory for the user to run programs but minimal in newer iphone 4+/ios 5.x since it uses arc and you can skip that if you use ARC projects.