@property definitions with ARC: strong or retain?

问题

Using Xcode 4.2 and ARC, I notice that the auto-generated code for an NSManagedObject still reads like this for properties:

@property (nonatomic, retain) NSString * someString;

1) Shouldn\'t retain now be replace with strong or weak?

2) Why does the auto-generated code still use retain

3) What is the correct replacement for retain in this property statement?

I\'m currently debugging a problem using NSFetchRequest, and I thought this might be the source of the problem. Thoughts?

回答1:

1) Shouldn't retain now be replace with strong or weak?

No. You cannot replace retain with weak; they are different. And strong is a 100% synonym for retain; they are identical. You can use either, so there is no "should" here. You can replace retain with strong if you like, but you don't have to.

2) Why does the auto-generated code still use retain

Why not? See (1). retain is correct so there is no problem.

3) What is the correct replacement for retain in this property statement?

There is no need to replace retain.

I'm currently debugging a problem using NSFetchRequest, and I thought this might be the source of the problem. Thoughts?

It isn't.

回答2:

To answer all three questions in one: retain and strong are synonymous with each other, so both are correct. The documentation states

retain implies __strong ownership

strong implies __strong ownership

回答3:

Before ARC, you have to 'release' an object which is retained. That mean retain has counter part. After ARC you don't need to release. So use strong. Its a visual clue that you don't need to call release.

回答4:

"retain" is equals to "strong".

"strong" is used for example:

@property (nonatomic, strong) NSString * someString;

And "__strong" is used for example:

-(void) someMethod
{
    __strong NSString* vStr = [[NSString alloc] initWithString:@"some string"];
}

On Apple Docs. says:

Property Attributes

The keywords weak and strong are introduced as new declared property attributes, as shown in the following examples.

// The following declaration is a synonym for: @property(retain) MyClass *myObject;
property(strong) MyClass *myObject;

Apple doc. http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html

来源：https://stackoverflow.com/questions/7796476/property-definitions-with-arc-strong-or-retain