iOS animationWithDuration 链接第一个动画未显示

Question

我有 2 个动画，其中一个动画调用另一个动画，但只有后者真正发生。我不确定问题是什么。我是 iOS 新手。我试图将其动画化为向上然后向下，但只发生向下。

此外，如果我将调用从 [self animateUp] 更改为 [self animateDown]，则不会发生动画。

-(void)viewDidLoad
{
    [super viewDidLoad];
    [self.containerView addSubview:self.logoView = ({
        UIImageView *imageView = [UIImageView new];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.image = [UIImage imageNamed:@"thisImage"];
        imageView;
    })];
    [self animateUp];
}

- (void)animateUp
{
    [UIView animateWithDuration:1 animations:^{
        CGRect newFrame = CGRectMake(self.logoView.frame.origin.x, self.logoView.frame.origin.y - 40, self.logoView.frame.size.width, self.logoView.frame.size.height);
        self.logoView.frame = newFrame;
    } completion:^(BOOL finished) {
        [self animateDown];
    }];
}

- (void)animateDown
{
    [UIView animateWithDuration:1 animations:^{
        CGRect newFrame = CGRectMake(self.logoView.frame.origin.x, self.logoView.frame.origin.y + 40, self.logoView.frame.size.width, self.logoView.frame.size.height);
    self.logoView.frame = newFrame;
    } completion:nil ];
}

Answer 1

对 animateUp 的调用发生在 ImageView 具有初始帧集之前。您可以将此延迟到 viewDidAppear 或 viewDidLayoutSubviews，应该会看到动画正确出现。

-(void)viewDidLoad
{
    [super viewDidLoad];
    [self.containerView addSubview:self.logoView = ({
        UIImageView *imageView = [UIImageView new];
        imageView.contentMode = UIViewContentModeScaleAspectFit;
        imageView.image = [UIImage imageNamed:@"thisImage"];
        imageView;
    })];
}

- (void) viewDidLayoutSubviews
{
    [self animateUp];    // at this point the ImageView has its frame set
}

请注意，viewDidAppear 和 viewDidLayoutSubviews 在 UIViewController 的生命周期中可能会被多次调用，因此如果您只希望动画发生一次，您需要适应这种情况。