iphone - 如何在采取行动之前知道几个区 block 是否已经执行完毕？

Question

在调用 removeFromSuperview: 之前，我正在使用 animateWithDuration:animations:completion: 移动我的用户界面的几个元素(大约 4 个元素)。

我的问题是，在调用 removeFromSuperview: 之前我怎么知道所有这些动画已经完成？

Answer 1

好吧，回答我自己的问题。

我最终做了这样的事情:

    // Create dispatch queue & group
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();

    // Two group enters
    dispatch_group_enter(group);
    dispatch_group_enter(group);

    // (notice the group parameter in dispatch_group_leave)
    [UIView animateWithDuration:0.3 animations:^{
        self.pickerView.frame = CGRectMake( self.pickerView.frame.origin.x
                                           , self.view.bounds.size.height + self.pickerView.frame.size.height/2
                                           , self.pickerView.frame.size.width
                                           , self.pickerView.frame.size.height);
    } completion:^(BOOL finished){
        dispatch_group_leave(group);
    }]; 


    [UIView animateWithDuration:0.3 animations:^{
        self.navigationBar.frame = CGRectMake( self.navigationBar.frame.origin.x
                                              , -self.navigationBar.frame.size.height
                                              , self.navigationBar.frame.size.width
                                              , self.navigationBar.frame.size.height);
    } completion:^(BOOL finished){
        dispatch_group_leave(group);
    }];

    // Finishing callback
    dispatch_group_notify(group, queue, ^{
        [self.view removeFromSuperview];
    });

    // Release the group
    dispatch_release(group);

我希望这可以作为其他人的榜样。