blocks|key|604683|text|这是因为从视图控制器中删除根视图。当您将UIViewController添加到故事板中时，您可以看到以下内容：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|604684|​|604685|📷|atomic|offset|length|604686|604687|如果删除此视图并添加UIImageView，则会看到以下内容：|604688|604689|604690|604691|604692|604693|604694|因此，添加UIView作为根视图，UIImageView作为根视图的单个子视图。然后，您可以使用约束：|604695|604696|604697|604698|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://developer.qcloudimg.com/http-save/yehe-900000/592e2b3fff6930d050cebd5c2f7861fc.png|imageAlt|1|https://developer.qcloudimg.com/http-save/yehe-900000/12c2e3fe68ddec6a702ea88729db24e8.png|2|https://developer.qcloudimg.com/http-save/yehe-900000/b2c14dcb6b93b62c042d29d2669bdf88.png|3|https://developer.qcloudimg.com/http-save/yehe-900000/5e154d04d3b4124791ef2b833f54ee7b.png^0|0|0|0|1|0|0|0|0|0|0|1|1|0|0|0|0|1|2|0|0|0|0|0|1|3|0|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1C|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1D|8|@]|9|@$G|1E|H|1F|1|1G]]|A|$]]|$1|I|3|C|5|6|7|1H|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|1I|8|@]|9|@]|A|$]]|$1|L|3|C|5|6|7|1J|8|@]|9|@]|A|$]]|$1|M|3|E|5|F|7|1K|8|@]|9|@$G|1L|H|1M|1|1N]]|A|$]]|$1|N|3|C|5|6|7|1O|8|@]|9|@]|A|$]]|$1|O|3|C|5|6|7|1P|8|@]|9|@]|A|$]]|$1|P|3|E|5|F|7|1Q|8|@]|9|@$G|1R|H|1S|1|1T]]|A|$]]|$1|Q|3|C|5|6|7|1U|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1V|8|@]|9|@]|A|$]]|$1|T|3|C|5|6|7|1W|8|@]|9|@]|A|$]]|$1|U|3|E|5|F|7|1X|8|@]|9|@$G|1Y|H|1Z|1|20]]|A|$]]|$1|V|3|C|5|6|7|21|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|22|8|@]|9|@]|A|$]]]|X|$Y|$5|Z|10|11|A|$12|13|14|-4]]|15|$5|Z|10|11|A|$12|16|14|-4]]|17|$5|Z|10|11|A|$12|18|14|-4]]|19|$5|Z|10|11|A|$12|1A|14|-4]]]]

This is because you remove root view from view controller. When you add UIViewController to storyboard you can see this:

<a href="https://i.stack.imgur.com/4tY2j.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4tY2j.png" alt="enter image description here"></a>

If you delete this view and add UIImageView you see this:

<a href="https://i.stack.imgur.com/Gz7c9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Gz7c9.png" alt="enter image description here"></a>

<a href="https://i.stack.imgur.com/PikvC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PikvC.png" alt="enter image description here"></a>

So add UIView as root and UIImageView as single subview of root view. And then you can play with constraints:

<a href="https://i.stack.imgur.com/k7EGV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/k7EGV.png" alt="enter image description here"></a>

blocks|key|604718|text|在我的例子中，Xcode+11.2以某种方式设置了我的UIButton+tranlates+mask+into+constraints的布局属性。所以我把它从尺寸检查器改成了automatic，它是固定的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|604719|entityMap^0|R|8|10|V|2F|9|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

In my case, Xcode 11.2 somehow set layout property of my <code>UIButton</code> <code>tranlates mask into constraints</code>. So I changed it to <code>automatic</code> from size inspector and it is fixed.

blocks|key|604735|text|如果你移动一个视图(如。移动它，然后离开一个TableView)，然后它将神秘地失去接受约束的能力。那就建一个新的。XCode+11.4.1|type|unstyled|depth|inlineStyleRanges|entityRanges|data|604736|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

if you move a View around (eg. move it IN then OUT a TableView) then it will mysteriously loose its ability to accept constraints. So build a new one.
XCode 11.4.1

blocks|key|1310116|text|不能设置约束的原因是图像视图不在视图中，而是基本视图。为了在任何类型的视图上设置约束，它必须在另一个视图中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1310117|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The reason you can't set the constraints is because your image view is not in a view, it is the base view. In order to set constraints on a view of any kind, it must be inside another view.

blocks|key|612250|text|自动布局约束要么是两个对象之间的关系，要么是大小约束。本例中只有一个对象，因此此处不适用任何自动布局约束。大小约束也不适用，因为这是xib的根视图。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|612251|不确定您在这里试图实现什么，但是如果您将UIImageView放在此视图控制器的content视图上而不是更改它的类，则会有完整的自动布局约束。|612252|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Auto layout constraints are either relationships between two objects or size constraints. You have only one object in this example, so no auto layout constraints are applicable here. Size constraints are also not applicable because this is the root view of your xib.

Not sure what you are trying to achieve here, but you would have full set of auto layout constraints if you placed your UIImageView on the content view of this view controller instead of changing its class.

blocks|key|1310048|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1310049|📷|atomic|offset|length|1310050|1310051|我所做的，干净和简单的是：-在您的视图中，添加UIImageView+-选择您的UIImageView+-点击“添加新约束”按钮(如附图所示)。|1310052|如您所见，选择了UIImageView。|1310053|唯一可能的解释是你可能忘了选择它。|1310054|干杯|1310055|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://developer.qcloudimg.com/http-save/yehe-900000/876a638d790cd8f6f5c1edb3507293c7.png|imageAlt^0|0|0|1|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@$E|10|F|11|1|12]]|A|$]]|$1|G|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|14|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|15|8|@]|9|@]|A|$]]|$1|L|3|M|5|6|7|16|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|17|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|Q|$R|$5|S|T|U|A|$V|W|X|-4]]]]

<a href="https://i.stack.imgur.com/XGWHr.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XGWHr.png" alt=" UIImageView Selected + Add New Constraints button"></a>

All I did, clean and simple was:
- At your view, add the UIImageView
- Select your UIImageView
- Click on the "Add New Constraints" button (shown in the attached picture).

As you can see, the UIImageView is selected.

The only possible explanation is that you may have forgotten to select it. 

Cheers

blocks|key|1310333|text|我也面临着同样的情况。但是在我的例子中，我尝试将imageview插入到水平堆栈视图中。奇怪的是，我无法为图像视图添加宽度和高度值的约束。只有在删除当前并添加新的imageview之后，我才能够添加约束。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1310334|entityMap^0|20|I|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I confronted with the same situation. But in my case, I tried to insert imageview into horizontal stack view. Strangely, I could not add constraints for width and height value for imageview.
I was able add the constraints only after deleting the current and adding a new imageview.

There are many guides out there that talk about auto-layout such as: <a href="http://www.raywenderlich.com/83129/beginning-auto-layout-tutorial-swift-part-1" rel="noreferrer">http://www.raywenderlich.com/83129/beginning-auto-layout-tutorial-swift-part-1</a> 

Now constraints don't seem to be super complicated except that when it comes to trying to set them on a UIImageView within a ViewController, With "Use Auto-Layout" ticked, I can't for the life of me set any constraints as when I click any of the three buttons used to achieve this, all the options for setting constraints is greyed out.

I'm sure this is something simple... little help?

I've found something in reference materials: "Constraint options that require multiple elements are disabled if you have only a single element selected." but in none of the guides do I have to have more than the UIImageView selected to set constraints. 

Edit: added images:

<a href="https://i.stack.imgur.com/D9Cmt.png" rel="noreferrer"><img src="https://i.stack.imgur.com/D9Cmt.png" alt="ContraintsGreyedOut1of2"></a>

<a href="https://i.stack.imgur.com/I7EKc.png" rel="noreferrer"><img src="https://i.stack.imgur.com/I7EKc.png" alt="ContraintsGreyedOut2of2"></a>

Xcode 6.4 - Unable to set constraints on Views or ... anything

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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有许多关于自动布局的指南，如：。现在约束似乎不太复杂，只是当尝试在UIImageView上设置约束时，加上“使用自动布局”，我无法设置任何约束，因为当我单击用于实现这一目标的三个按钮中的任何一个时，设置约束的所有选项都是灰色的。我相信这很简单..。帮个小忙？我在参考资料中发现：“如果只选择一个元素，那么需要多个元素的约束选项就会被禁用。”但是，在所有的指南中，我都必须选择比选择UIImageVie

问Xcode 6.4 -无法对视图设置约束或.什么都行
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