使用block時如何避免循環引用

RT

- (void)dealloc
{
 
    NSLog(@"no cycle retain");
}
 
- (id)init
{
    self = [super init];
    if (self) {
 
#if TestCycleRetainCase1
 
        //會循環引用
        self.myblock = ^{
 
            [self doSomething];
        };
#elif TestCycleRetainCase2
 
        //會循環引用
        __block TestCycleRetain *weakSelf = self;
        self.myblock = ^{
 
            [weakSelf doSomething];
        };
 
#elif TestCycleRetainCase3
 
        //不會循環引用
        __weak TestCycleRetain *weakSelf = self;
        self.myblock = ^{
 
            [weakSelf doSomething];
        };
 
#elif TestCycleRetainCase4
 
        //不會循環引用
        __unsafe_unretained TestCycleRetain *weakSelf = self;
        self.myblock = ^{
 
            [weakSelf doSomething];
        };
 
#endif
 
        NSLog(@"myblock is %@", self.myblock);
 
    }
    return self;
}
 
- (void)doSomething
{
    NSLog(@"do Something");
}
 
int main(int argc, char *argv[]) {
    @autoreleasepool {
        TestCycleRetain* obj = [[TestCycleRetain alloc] init];
        obj = nil;
        return 0;
    }
}

經過上面的測試發現，在加了__weak和__unsafe_unretained的變量引入後，TestCycleRetain方法可以正常執行dealloc方法，而不轉換和用__block轉換的變量都會引起循環引用。
因此防止循環引用的方法如下：
__unsafe_unretained TestCycleRetain *weakSelf = self;