动画无法在同时满足约束条件 [英] Unable to simultaneously satisfy constraints when animating

问题描述

我有IB六个用户限制设​​置看起来像这样的：

I have six user constraints setup with IB that look like this:

H:|-(593)-[UIView(411)]-(20)-|
V:|-(20)-[UIView(288)]-(396)-|

我长大和收缩，通过改变约束条件，然后调用layoutIfNeeded的看法。例如，成长的看法，我会做的事：

I grow and shrink the view by changing the constraints and then calling layoutIfNeeded. For example, to grow the view I will do:

H:|-(20)-[UIView(984)]-(20)-|
V:|-(20)-[UIView(663)]-(20)-|

然后调用

[UIView animateWithDuration:.5 animations:^{
    [self.view layoutIfNeeded];
}];

此技术的发展和缩小我的观点，它看起来不错，但我给予了相当混乱的警告：

This technique grows and shrinks my view, and it looks nice, but I'm given a rather confusing warning:

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x148d5af0 H:[UIView:0x148d4e50(411)]>",
    "<NSLayoutConstraint:0x148cc940 H:[UITableView:0xace7600(319)]>",
    "<NSLayoutConstraint:0x148ce040 H:|-(NSSpace(20))-[UITableView:0xacd4e00]   (Names: '|':UIView:0x148cddd0 )>",
    "<NSLayoutConstraint:0x148cdf00 H:[UITableView:0xace7600]-(NSSpace(20))-|   (Names: '|':UIView:0x148cddd0 )>",
    "<NSLayoutConstraint:0x148cdea0 H:[UITableView:0xacd4e00]-(NSSpace(8))-[UITableView:0xace7600]>",
    "<NSLayoutConstraint:0x148d4c10 UIView:0x148cddd0.trailing == UIView:0x148cdd40.trailing>",
    "<NSLayoutConstraint:0x148d4b90 H:|-(0)-[UIView:0x148cddd0]   (Names: '|':UIView:0x148cdd40 )>",
    "<NSLayoutConstraint:0x148d6020 H:|-(320)-[UIView:0x148cdd40]   (Names: '|':UIView:0x148cd330 )>",
    "<NSLayoutConstraint:0x148d5fa0 UIView:0x148cdd40.trailing == UIView:0x148cd330.trailing>",
    "<NSLayoutConstraint:0x148d5f60 H:[UIView:0x148d4e50]-(NSSpace(20))-|   (Names: '|':UIView:0x148cd330 )>",
    "<NSLayoutConstraint:0x148d5ee0 H:|-(20)-[UIView:0x148d4e50]   (Names: '|':UIView:0x148cd330 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x148cc940 H:[UITableView:0xace7600(319)]>

现在所有这些约束是由IB产生。我有双^（三倍！）选中此。我已经把这些限制连同笔和纸，并已经得到了这一点：

Now all of these constraints are generated by IB. I've double^(triple!) checked this. I've put these constraints together with a pen and paper and have gotten this:

UIView_A H:[-(20)-[UIView_E]-(20)-] and H:[-(320)-(UIView_B)
UIView_B H:[-(0)-[UIView_D]
UIView_C H:[UIView_C(411)]
UIView_D H:[-(20)-[UITableView_F]-[UITableView_G(319)]-(20)-]

我不明白这些限制怎么也无法得到满足。他们看起来很好。我不改变他们，他们正在通过IB生成的。不是由IB产生约束自动满足的？

I don't understand how these constraints can't be satisfied. They look fine. I don't change them and they're generated by IB. Aren't constraints generated by IB automatically satisfiable?

或者，至少，有没有办法阻止警告？它完美的表现，我也不需要看到的是它打破似乎并不反正做任何事情的约束。

Or, at a minimum, is there a way to stop warnings? It behaves perfectly and I don't need to see that it's breaking a constraint that doesn't seem to do anything anyway.

推荐答案

所以，事实证明，在这我改变制约事项的顺序。

So, it turns out, the order at which I change constraints matters.

要增长的观点，我会

1. 增加宽度：H：| - （593） - [UIView的（ 984 ）] - （20） - |


2. 降低前导空格：H：| - （ 20 ） - [UIView的（984） - （20） - |

1. Increase the width: H:|-(593)-[UIView(984)]-(20)-|
2. Decrease the leading space: H:|-(20)-[UIView(984)]-(20)-|

这不会产生任何警告。但是，如果我这样做了相反的顺序，我会得到一个警告：

This produces no warnings. However, if I do this in the opposite order, I'll get a warning:

Unable to simultaneously satisfy constraints.
Probably at least one of the constraints ...

...Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x1567f650 H:[UITableView:0x119e6200(319)]>

在萎缩的观点，我复制了code，它增加了宽度（具有相同的顺序），只是改变了值。这给了我我张贴在我原来的问题的警告。当我切换顺序萎缩，消失的警告。

When shrinking the view, I copied the code that increased the width (with the same order) and just changed the values. That gave me the warning I posted in my original question. When I switched the order for shrinking, the warnings disappeared.

为什么会出现这种情况？我不知道。我发现更多的我会及时更新。

Why is this the case? I don't know. I'll update as I discover more.

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