首次显示视图控制器的视图时,我想运行一个动画,其中视图控制器中的所有元素从屏幕底部外部滑动到其自然位置.为此,我在viewDidLayoutSubviews中执行subview.frame.origin.y = self.view.frame.size.height.我也尝试过viewWillAppear,但它根本不起作用.然后我使用viewDidAppear中的subview.frame.origin.y – = self.view.frame.size.height将它们设置为自然位置.

问题是viewDidLayoutSubviews在整个视图控制器的生命周期中被调用了好几次.因此,当显示键盘的事情发生时,我的所有内容都会再次在视图之外被替换.

这样做有更好的方法吗？我是否需要添加某种标志来检查动画是否已经运行？

编辑：这是代码.这里我在viewDidLayoutSubviews中调用prepareAppearance,它可以工作,但是在整个控制器的生命周期中多次调用viewDidLayoutSubviews.

- (void)viewDidLayoutSubviews
{
    [super viewDidLayoutSubviews];
    [self prepareAppearance];
}

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self animateAppearance];
}


- (NSArray *)animatableViews
{
    return @[self.createAccountButton,self.facebookButton,self.linkedInButton,self.loginButton];
}

- (void)prepareAppearance
{
    NSArray * views = [self animatableViews];
    NSUInteger count = [views count];

    for (NSUInteger it=0 ; it < count ; ++it) {

        UIView * view = [views objectAtIndex:it];
        CGRect frame = view.frame;

        // Move the views outside the screen,to the bottom
        frame.origin.y += self.view.frame.size.height;

        [view setFrame:frame];
    }
}

- (void)animateAppearance
{
    NSArray * views = [self animatableViews];
    NSUInteger count = [views count];

    for (NSUInteger it=0 ; it < count ; ++it) {

        __weak UIView * weakView = [views objectAtIndex:it];
        CGRect referenceFrame = self.view.frame;

        [UIView animateWithDuration:0.4f
                              delay:0.05f * it
                            options:UIViewAnimationOptionCurveEaSEOut
                         animations:^{

                             CGRect frame = weakView.frame;
                             frame.origin.y -= referenceFrame.size.height;

                             [weakView setFrame:frame];
                         }
                         completion:^(BOOL finished) {
                         }];
    }
}