iOS 动画与持续时间链接第一个动画未显示

Question

>我有 2 个动画，一个调用另一个，但实际上只有后者在发生。我不确定问题是。我是iOS新手。我正在尝试先上下动画，但只有向下发生。

另外，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 设置初始帧之前。 您可以将其推迟到viewDidAppear或viewDidLayoutSubviews，并且应该会看到动画正确发生。

-(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 可能会在 UIViewController 的生命周期中被多次调用，因此，如果您只希望动画出现一次，则需要适应这种情况。