自动布局约束更改不会设置动画 [英] Auto Layout constraint change does not animate

问题描述

我正在使用教程中的动画学习自动布局

I was learning the auto layout with animations from the tutorial

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

并且事情进展顺利。

当我尝试在我的应用程序中使用此概念时，尝试从下到上设置屏幕（UIView）的动画效果，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,

但是如果我添加一个UILabel作为此设置屏幕的子视图，动画就消失了。
从设置屏幕中删除此UILabel时，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.

以下是我已连接的插座

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

查看加载设置方法（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;
}

我的问题类似于
UIView自动布局动画问题

推荐答案

我找到了答案。

而不是，

[settingsView layoutIfNeeded];

此行使其像魅力一样工作，

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尝试动画的视图。

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的评论所指出的，这是 iOS 7，iOS 10所必需的即可。
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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