使用block时如何避免循环引用

RT

- (void)dealloc
{

NSLog(@"no cycle retain");
}

- (id)init
{
self = [super init];
if (self) {

#if TestCycleRetainCase1

//会循环引用
self.myblock = ^{

[self doSomething];
};
#elif TestCycleRetainCase2

//会循环引用
__block TestCycleRetain *weakSelf = self;
self.myblock = ^{

[weakSelf doSomething];
};

#elif TestCycleRetainCase3

//不会循环引用
__weak TestCycleRetain *weakSelf = self;
self.myblock = ^{

[weakSelf doSomething];
};

#elif TestCycleRetainCase4

//不会循环引用
__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;
}
}

经过上面的测试发现，在加了__weak和__unsafe_unretained的变量引入后，TestCycleRetain方法可以正常执行dealloc方法，而不转换和用__block转换的变量都会引起循环引用。

因此防止循环引用的方法如下：

__unsafe_unretained TestCycleRetain *weakSelf = self;