1 介绍

约束布局是Google官方推出新的布局解决方案，能够解决布局嵌套过深问题，同时还能够简化布局所需要的时间。之前在beta版本就使用了，使用中可能会报错的情况已经解决，而且还带来了ratio的设置，同时Studio升级到2.3后视图预览效果比较好。官方现在主推这个布局，新建的Activity都是ConstraintLayout默认了。

ConstraintLayout is available in an API library that’s
compatible with Android 2.3 (API level 9) and higher. This page provides a guide
to building a layout with ConstraintLayout in Android Studio 2.3 or higher. If
you’d like more information about the Layout Editor itself, see the Android
Studio guide to Build a UI with Layout Editor.

2
使用前配置

To use ConstraintLayout in your project, proceed as
follows:

Ensure you have the latest Constraint Layout
library: 
1.
Click Tools > Android > SDK Manager. 
2. Click the SDK Tools tab. 
3.Expand Support Repository and then check
ConstraintLayout for Android and Solver for ConstraintLayout. Check Show Package
Details and take note of the version you’re downloading (you’ll need this
below). 
4.Click
OK. 
5.
Add the library as a dependency in your module-level build.gradle
file: 
dependencies { 
compile
'com.android.support.constraint:constraint-layout:1.0.1' 
} 
The library version you download may be higher,
so be sure the value you specify here matches the version from step 3. 
6. In the toolbar or sync notification, click
Sync Project with Gradle Files. 
Now you’re ready to build your layout with
ConstraintLayout.

3
重点内容

• Control
  linear groups with a chain
• Set size as a
  ratio
• Constrain to
  a guideline