由@davidpbr ConstraintLayout性能报告

我做了两个类似的7个子布局，每个都有一个父ConstraintLayout和RelativeLayout。 基于Android Studio方法跟踪工具，它似乎ConstraintLayout花更多的时间在onMeasure和执行额外的工作在onfinishinflation。

使用的库(support-v4, appcompat-v7…):

com.android.support.constraint: constraint-layout: 1.0.0-alpha1

设备/Android版本转载于: 三星Galaxy S6 (SM-G920A;对不起，没有Nexus atm)。Android 5.0.2

快速方法跟踪比较:

示例Github回购:https://github.com/OnlyInAmerica/ConstraintLayoutPerf

ConstraintLayout的目的是通过对每个视图应用一些规则来避免嵌套，从而优化和平抑布局的视图层次结构。

规则类似于RelativeLayout，例如将底边设置为其他视图的底部。

app:layout_constraintBottom_toBottomOf="@+id/view1"

与RelativeLayout不同的是，ConstraintLayout提供了一个偏置值，用于相对于手柄(用红圈标记)的0%和100%水平和垂直偏移来定位视图。这些百分比(和分数)提供了视图在不同屏幕密度和大小之间的无缝定位。

app:layout_constraintHorizontal_bias="0.33" <!-- from 0.0 to 1.0 -->
app:layout_constraintVertical_bias="0.53" <!-- from 0.0 to 1.0 -->

Baseline句柄(圆角的长管道，在圆句柄的下面)用于将视图的内容与另一个视图引用对齐。

正方形句柄(在视图的每个角落)用于在dps中调整视图的大小。

这完全是基于个人观点和我对ConstraintLayout的印象

真正要问的问题是，是否有理由使用约束布局以外的任何布局?我相信答案可能是否定的。

对于那些坚持认为它们是针对新手程序员或类似的人，它们应该提供一些理由来证明它们不如其他任何布局。

约束布局在各个方面都更好(它们的APK大小确实花费了150k)。它们更快、更简单、更灵活，能够更好地应对变化，能够在项目消失时修复问题，能够更好地适应完全不同的屏幕类型，并且不会使用一堆嵌套的循环和长长的树形结构。你可以把任何东西放在任何地方，相对于任何地方。

它们在2016年年中有点古怪，可视化布局编辑器不够好，但它们已经到了这样的地步，如果你有一个布局，你可能会认真考虑使用约束布局，即使它做的事情与RelativeLayout相同，甚至是一个简单的线性布局。框架布局显然仍然有他们的目的。但是，在这一点上，我看不到任何其他东西。如果从这个开始，就不会再加其他东西了。

正式来说，ConstraintLayout要快得多

在Android N版本中，ConstraintLayout类提供了与RelativeLayout类似的功能，但成本要低得多。

以下是它们的区别/优点:

Constraint Layout has dual power of both Relative Layout as well as Linear layout: Set relative positions of views ( like Relative layout ) and also set weights for dynamic UI (which was only possible in Linear Layout). A very powerful use is grouping of elements by forming a chain. This way we can form a group of views which as a whole can be placed in a desired way without adding another layer of hierarchy just to form another group of views. In addition to weights, we can apply horizontal and vertical bias which is nothing but the percentage of displacement from the centre. ( bias of 0.5 means centrally aligned. Any value less or more means corresponding movement in the respective direction ) . Another very important feature is that it respects and provides the functionality to handle the GONE views so that layouts do not break if some view is set to GONE through java code. More can be found here: https://developer.android.com/reference/android/support/constraint/ConstraintLayout.html#VisibilityBehavior Provides power of automatic constraint applying by the use of Blue print and Visual Editor tool which makes it easy to design a page.

所有这些特性都使视图层次结构变得平坦，从而提高了性能，还有助于制作响应性和动态的UI，从而更容易适应不同的屏幕尺寸和密度。

这里是快速学习的最佳地点: https://codelabs.developers.google.com/codelabs/constraint-layout/#0

The only difference i've noted is that things set in a relative layout via drag and drop automatically have their dimensions relative to other elements inferred, so when you run the app what you see is what you get. However in the constraint layout even if you drag and drop an element in the design view, when you run the app things may be shifted around. This can easily be fixed by manually setting the constraints or, a more risky move being to right click the element in the component tree, selecting the constraint layout sub menu, then clicking 'infer constraints'. Hope this helps