Recommended way to declare delegate properties with ARC

问题

I used to declare all delegate properties as

@property (assign) id<FooDelegate> delegate;

I was under the impression that all assign properties should now be weak pointers, is this correct? If I try to declare as:

@property (weak) id<FooDelegate> delegate;

I get an error while trying to @synthesize (autogenerated weak properties are not supported).

What's the best practice in this case?

回答1:

Use __unsafe_unretained instead weak for ARC projects targeting iOS 4 and 5. The only difference is that weak nils the pointer when deallocated, and it's only supported in iOS 5.

Your other question is answered in Why are Objective-C delegates usually given the property assign instead of retain?.

回答2:

Xcode 4 Refactor > Convert to Objective-C ARC transforms:

@interface XYZ : NSObject
{
    id delegate;
}
@property (assign) id delegate;
...
@synthesize delegate;

into:

@interface XYZ : NSObject
{
    id __unsafe_unretained delegate;
}
@property (unsafe_unretained) id delegate;
...
@synthesize delegate;

If I remember correctly it is also mentioned in WWDC 2011 video about ARC.

来源：https://stackoverflow.com/questions/7753841/recommended-way-to-declare-delegate-properties-with-arc