iOS __weak __strong WeakSelf StrongSelf

在block中常常会用到self，可是会造成循环引用。这时候就需要这样来解决这个问题：

#define WeakSelf __weak typeof(self) weakSelf = self
#define StrongSelf __strong typeof(weakSelf) self = weakSelf

//OC
- (void)aFunc:(id)sender {

    WeakSelf;//
    [UIView animateWithDuration: animations:^{
        StrongSelf;//
        [self.view doSomething];//use self
    }];
}

//swift 2.2
self.closure = { [unowned self] in
    self.doSomething()
}