自动布局约束更改没有动画 [英] Auto Layout constraint change does not animate

问题描述

我从教程中学习了带有动画的自动布局

I was learning the auto layout with animations from the tutorial

http://weblog.入侵code.com/post/42362079291/auto-layout-and-core-animation-auto-layout-was

一切都很完美.

当我尝试在我的应用程序中使用这个概念时，尝试从下到上为设置屏幕(一个 UIView)设置动画，当设置屏幕只是一个空的 UIView 时效果很好，

When I tried to use this concept in my application, trying to animate a settings screen(a UIView) from bottom to top,it works great when the settings screen is just an empty UIView,

但如果我将 UILabel 作为子视图添加到此设置屏幕，动画就会消失.从设置屏幕中删除此 UILabel 后，动画可见.

But in case I add a UILabel as a subview to this settings screen, the animation just vanishes. On removing this UILabel form the settings screen, the animation is visible.

这是我连接的插座

__weak IBOutlet UIView *settingsView;
__weak IBOutlet NSLayoutConstraint *settingsBottomConstraint;
__weak IBOutlet NSLayoutConstraint *settingsViewHeightConstraint;

View 确实加载了设置方法(setupViews)

View did load setup method(setupViews)

-(void)setupViews
{
    settingsBottomConstraint.constant = - settingsViewHeightConstraint.constant;
    [settingsView setNeedsUpdateConstraints];
    [settingsView layoutIfNeeded];
    isSettingsHidden = YES;
}

隐藏/取消隐藏方法

- (IBAction)showSettingsScreen:(id)sender {

    if (isSettingsHidden) {

        settingsBottomConstraint.constant = 0;
        [settingsView setNeedsUpdateConstraints];
        [UIView animateWithDuration:.3 animations:^{
            [settingsView layoutIfNeeded];
        }];
    }
    else{

        settingsBottomConstraint.constant = - settingsViewHeightConstraint.constant;
        [settingsView setNeedsUpdateConstraints];
        [UIView animateWithDuration:0.3 animations:^{
            [settingsView layoutIfNeeded];
        }];

    }
    isSettingsHidden = !isSettingsHidden;
}

我的问题似乎与UIView 自动布局动画问题

推荐答案

我找到了答案.

取而代之，

[settingsView layoutIfNeeded];

这条线使它像魅力一样工作，

this line made it worked like charm,

[self.view layoutIfNeeded];

我想我们需要在父视图上执行 layoutIfNeeded 方法，而不仅仅是我们想要制作动画的视图.

I suppose we need to perform layoutIfNeeded method on the parent view not just the view we are trying to animate.

更新:正如 codyko 在评论中指出的那样，这是 iOS 7、iOS 10 所必需的.对于 iOS 8，此问题不存在.

UPDATE: As pointed out in a comment by codyko, this is required for iOS 7, iOS 10. For iOS 8 this issue does not exists.

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