CODEWITHSUNDEEP
iosobjective-cmemory-management
George
George

Reputation: 3619

Is it possible or necessary to synthesize/release weak property in manual retain-release mode

For example, I subclass UIView, in which a weak property called myString is defined. There is an error message for @synthesize myString = _myString; statement: Semantic Issue: @synthesize of 'weak' property is only allowed in ARC or GC mode.

The MyUIView.h file:

@interface MyUIView : UIView

@property (nonatomic, weak) NSString *myString;

@end

The MyUIView.m file:

#import "MyUIView.h"

@implementation MyUIView

@synthesize myString = _myString; // This statement causes an error whose message is Semantic Issue: @synthesize of 'weak' property is only allowed in ARC or GC mode

- (void)dealloc
{
    [_myString release];

    [super dealloc];
}

// Other methods

@end

Then I removed the @synthesize myString = _myString; and there goes another error for this statement [_myString release]; as Semantic Issue: Use of undeclared identifier '_text'

If it's not necessary to synthesize nor release a weak property like myString above, should I re-write the code like this:

The MyUIView.h file:

@interface MyUIView : UIView

@property (nonatomic, weak) NSString *myString;

@end

The MyUIView.m file:

#import "MyUIView.h"

@implementation MyUIView

- (void)dealloc
{        
    [super dealloc];
}

// Other methods

@end

Upvotes: 1

Views: 900

Answers (2)

Jesse Naugher
Jesse Naugher

Reputation: 9810

NSString (and any other class that is immutable with a mutable subclass) should be synthesized to copy. 

@property (copy) NSString *myString;

the first comment: Yes. (nonatomic, copy) is fine.

the second comment: You don't need to, it is assumed as well in modern objective-c syntax. There will be a _myString ivar created either way. Yes you need to release _myString if you use copy

Upvotes: 0

Gabriele Petronella
Gabriele Petronella

Reputation: 108101

weak is a valid property attribute only when ARC (or GC) is enabled.

You can either switch to ARC (strongly advisable) or use an assign or unsafe_unretained attribute instead, at the cost of losing the benefit of a weak reference (see Whats the difference between 'weak' and 'assign' in delegate property declaration)

That being said, I think both assign and weak won't accomplish anything desirable in the specific case.

Unless you really want to avoid a strong reference to that string, the appropriate property declaration would go as follows:

@property (nonatomic, copy) NSString *myString;

On why copy and not retain (or strong), you can read NSString property: copy or retain?

Upvotes: 7

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