How to make weak self in MRC?

问题

Message *m = [msg retain];
dispatch_queue_t queue = _handle_queue;
__block ProtocolDriver* blockSelf = self;
dispatch_async(queue, ^{
    if (blockSelf.protocol_delegate && [blockSelf.protocol_delegate respondsToSelector:@selector(onReceive:)]) {
        [blockSelf.protocol_delegate onReceive:m];
    }
});

I have a MRC objective-c file, which need run some code in block asynchronously.

But I thought the blockself is not safe since it is not weak pointer, Should I change it to true weak pointer.

@interface WeakPtr : NSObject
@property (nonatomic, weak) id realObj;
@property (nonatomic, assign) bool released;
@end
@implementation WeakPtr
@end

set the released when the MRC-object is dealloced, and test it in block

@property (nonatomic, retain) WeakPtr* selfPtr;
- (id)init{
    ...
    self.selfPtr = [[[WeakPtr alloc] init] autorelease];
    self.selfPtr.realObj = self;
}

- (void)dealloc
{
    ...
    self.selfPtr.released = true;
}

-(void)pump: (Message *)msg
{
    Message *m = [msg retain];
    dispatch_queue_t queue = _handle_queue;

    __block WeakPtr* weakSelf = self.selfPtr;
    dispatch_async(queue, ^{
        if (!weakSelf.released && [weakSelf.protocol_delegate respondsToSelector:@selector(onReceive:)]) {
            [weakSelf.protocol_delegate onReceive:m];
        }
    });
}

回答1:

Yes, definitely.

1) make a ARC weak pointer wrapper class.

@interface WeakPtr : NSObject
@property (nonatomic, weak) id realObj;
@end
@implementation WeakPtr
@end

2) use the ARC weak pointer wrapper in MRC to wrap the strong pointer.

-(void)pump: (Message *)msg
{
    Message *m = [msg retain];
    dispatch_queue_t queue = _handle_queue;
    WeakPtr* weakPtr = [WeakPtr new];
    weakPtr.realObj = self;
    dispatch_async(queue, ^{
        if ([weakPtr.realObj.protocol_delegate respondsToSelector:@selector(onReceive:)]) {
            [weakPtr.realObj.protocol_delegate onReceive:m];
        }
        [weakPtr release];
    });
}

Another option is -fobj-weak compiler flag.

回答2:

Short answer: You can't. The weak qualifier is a feature of ARC. In MRC, the type is assign, and it's equivalent to ARC's unsafe_unretained type.

MRC does not have an auto-niling weak type.

Edit:

Ok, perhaps "you can't" was too strong. Better to say:

MRC doesn't support auto niling weak references and you would have to handle it with app-level code, or a library that does it for you.

来源：https://stackoverflow.com/questions/40966421/how-to-make-weak-self-in-mrc