Should I release NSString before assigning a new value to it?

Question

Please give me some suggestions about how to change a NSString variable.

At my class, I set a member var:

NSString *m_movieName;
...
@property(nonatomic, retain) NSString *m_movieName;

At viewDidLoad method, I assign a default name to this var:

-(void)viewDidLoad{
NSString *s1 = [[NSString alloc] initWithFormat:@"Forrest Gump"];
self.m_movieName = s1;
...
[s1 release];
[super viewDidLoad]
}

At some function, I want to give a new name to this var, so I did like:

-(void)SomeFunc{
NSString *s2 = [[NSString alloc] initWithFormat:@"Brave Heart"];
//[self.movieName release]; // ??????? Should perform here?
self.m_moiveName = s2;
[s2 release];
}

I know, NSString* var is just a pointer to an allocated memory block, and 'assign' operation will increment this memory block's using count. For my situation, should I release m_movieName before assigning a value to it? If I do not release it (via [self.movieName release]), when and where will the previous block be released? Thanks for your help very much!

Answer 1

No, you have declared your property as retain, which means your object will retain the properties value. The synthesized (=compiler generated) setter will take care of releasing the old NSString before assigning a new value, so you don't have to manage this yourself.

Be careful when accessing the backing store for the property directly (m_movieName in your instance) as bypassing the setter won't release the current value automatically.

Answer 2

First of all, my advice would be, if you are using a NSString property, use copy instead of retain. Check this SO question out for details.

@property(nonatomic, copy) NSString *m_movieName;