约束2个视图时，ConstraintLayout怪异的属性行为 [英] ConstraintLayout weird attributes behavior when constraining 2 views

问题描述

假设我要使用app:layout_constraintTop_toTopOf将一个视图连接到另一个视图(可以是任何其他约束).

Let's say that I want to connect one view to another with app:layout_constraintTop_toTopOf (it can be any other constraint).

如果我将通过XML显示手动进行操作，则将如下所示:

If I will do it manually from the XML display it will be something like this:

 app:layout_constraintTop_toTopOf="@id/something"

但是-如果我使用设计选项而不是XML选项做同一件事，由于某种原因，我将获得额外的+(自动生成)字符它看起来像这样:

But - If I will do the same thing with the design option and not the XML option I will get extra + (auto generated) char for some reason and it will look like this :

  //notice the extra + in @+id
  app:layout_constraintTop_toTopOf="@+id/something"`

现在有趣的是，该应用程序可以在带有或不带有+字符的情况下运行.

Now the funny thing is that the app will run with or without the + char.

所以-看起来我在引用其他视图时确实不需要多余的+字符，我的问题是为什么正在发生，并且如何我可以防止android工作室布局编辑器中添加此+.

So - looks like I don't really need that extra + char while referring to other views, my question is why this is happening and how can I prevent android studio layout editor to add this +.

推荐答案

仅在xml中第一次提及ID时才需要+ id.

The +id is only needed the first time an id is mentioned in the xml.

每次以后都要使用+还是很有用的，以防将来要对xml重新排序.

It can still be useful to have the + every time in case you want to reorder the xml in the future.

我对此不会太担心.进行+ id可能会大大降低构建时性能. (看看您是否可以衡量差异.我怀疑您可以.)

I would not worry too much about this. Doing +id likely has an extremely low build-time performance hit. (See if you can measure the difference. I doubt you can.)

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