子视图的viewDidAppear

Question

我想在按钮被按下时加载一些数据，并在加载时将“加载视图”显示为当前视图的子视图。

所以我只想在子视图出现后才开始加载。如果不是这样，我的UI就会在没有通知的情况下卡住(子视图只有在加载完成后才会显示)。

有没有办法在子视图中使用像viewDidAppear这样的东西？

像这样在addSubview:之后立即做这项工作是行不通的：

- (void)doSomeWorkAndShowLoadingView
{
    UIView *loadingView = [[[UIView alloc] initWithFrame:self.view.frame] autorelease];
    loadingView.backgroundColor = [UIColor redColor];
    [self.view addSubview:loadingView];
    [self doSomeWork];
    [loadingView removeFromSuperview];
}
- (void)doSomeWork
{ 
    sleep(5);
}

(我不想在新线程上加载，因为我正在处理的是CoreData，它不是线程安全的)。

谢谢!

Answer 1

我找到了一个解决方案：

添加带有动画的子视图，我可以使用- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag来调用类似于子视图代理的subviewDidAppear之类的东西。

在UIView的子类中：

#define KEY_SHOW_VIEW @"_ShowLoadingView_"
#define KEY_HIDE_VIEW @"_HideLoadingView_"
- (void)addToSuperview:(UIView *)theSuperview
{

    [theSuperview addSubview:self];   

    CATransition *animation = [CATransition animation];
    [animation setDuration:0.2];
    [animation setType:kCATransitionFade];
    [animation setDelegate:self];
    [animation setRemovedOnCompletion:NO];
    [animation setValue:KEY_SHOW_VIEW forKey:@"animation_key"];
    [[theSuperview layer] addAnimation:animation forKey:nil];

}

- (void)removeFromSuperview
{
    CATransition *animation = [CATransition animation];
    [animation setDuration:0.2];
    [animation setType:kCATransitionFade];
    [animation setDelegate:self];
    [animation setRemovedOnCompletion:NO];
    [animation setValue:KEY_HIDE_VIEW forKey:@"animation_key"];
    [[self.superview layer] addAnimation:animation forKey:nil]; 

    [super removeFromSuperview];
}

- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag
{    
    NSString* key = [anim valueForKey:@"animation_key"];
    if ([key isEqualToString:KEY_SHOW_VIEW]) {
        if (self.delegate) {
            if ([self.delegate respondsToSelector:@selector(loadingViewDidAppear:)]) {
                [self.delegate loadingViewDidAppear:self];
            } 
        }
    } else if ([key isEqualToString:KEY_HIDE_VIEW]){
        [self removeFromSuperview];
    }
}

这让我得到了我想要的结果。

再次感谢您的帮助！

Answer 2

您应该能够直接在调用[parentView addSubview:loadingView]之后开始加载，或者在加载视图(假设它是子类的)中重写didMoveToSuperview，如下所示：

- (void)didMoveToSuperview {
    // [self superview] has changed, start loading now...
}