ConstraintLayout笔记

2017-03-30

ConstraintLayout

ConstraintLayout靠Constraints来组织view，其内的view hierarchy只有一层。在布局的时候，通过构造以下3者的关系来入手：

ConstraintLayout（parent）
sibling view
guideline

Anchor

每个view都有top, bottom, left(start),right(end)4个锚点，其中：

text-based views 会有 baseline anchor
guideline有 android:orientation=”vertical/horizontal” 两种模式，vertical时有左右锚点，horizontal时有上下锚点

Guideline

guideline是view的子类，只不过宽高为0，visibility为gone，只是为了布局提供瞄点而存在。guideline可以以绝对值或百分比的方式放置位置
绝对值：

layout_constraintGuide_begin
layout_constraintGuide_end

百分比

layout_constraintGuide_Percent

Xml Format

layout_constraint[SourceAnchor]_[TargetAnchor]="[TargetId]"

<Button
  android:id="@+id/button_cancel"
  … />

<Button
  android:id="@+id/button_next"
  app:layout_constraintStart_toEndOf="@+id/button_cancel"
  … />

Bias

the bias attributes:

layout_constraintHorizontal_bias
layout_constraintVertical_bias

app:layout_constraintVertical_bias=”0.25”Now the view is weighted with a 25/75 split of the available space on each axis.Technically, when no bias constraint is present, the bias is 0.5.

视图编辑器自动生成的属性

Autoconnect

tools:layout_editor_absoluteX
tools:layout_editor_absoluteY

保存当前状态，帮助视图编辑器绘制预览

Inference

tools:layout_constraint[Anchor]_creator

帮助视图编辑器区分哪些constraints是手动添加的，哪些是通过inference自动添加的

View Measurements

Exact
Wrap Content
Any Size (Measure to fill the available space for the attached constraints, Set layout_width or layout_height to 0dp)

android:minWidth / android:minHeight will be used by ConstraintLayout when its dimensions are set to WRAP_CONTENT.

Ratio

layout_constraintDimensionRatio = "width:height"
layout_constraintDimensionRatio = "H,width:height" //H/W为需要动态调整的一方
layout_constraintDimensionRatio = "floatValue[width/height]"

constraintDimensionRatio属性默认是『宽:高』，当然，你可以指定是谁比谁，例如『宽:高』实际上等效于『W,宽:高』，也等效于『H,高:宽』。

<ImageView
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:src="@drawable/water"
    app:layout_constraintDimensionRatio="1:3"/>

<ImageView
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:src="@drawable/water"
    app:layout_constraintDimensionRatio="0.3"/>

Visibility behavior

Margins when connected to a GONE widget
When a position constraint target’s visibility is View.GONE, you can also indicates a different margin value to be used using the following attributes:

layout_goneMarginStart
layout_goneMarginEnd
layout_goneMarginLeft
layout_goneMarginTop
layout_goneMarginRight
layout_goneMarginBottom

Chains

两个互相链接的view产生一个chain
Chains are controlled by attributes set on chain head: the head is the left-most widget for horizontal chains, and the top-most widget for vertical chains.

Chain Style
通过layout_constraintVertical_chainStyle 给chain设置不同的chain_style后，chain的行为会有不同的表现 (默认CHAIN_SPREAD)

Weighted chains
chain默认平分可用空间，layout_constraintHorizontal_weight 和layout_constraintVertical_weight 以正比的关系分配剩余空间。

等比例布局 在Android Studio中，选中要等比例布局的所有控件，点击右键选择『Center in Horizontal』即可完成对这些控件Chain的创建。创建好Chain后，就可以对这几个控件进行比例布局。

动态构造ConstraintLayout

ConstraintSet可以动态构造ConstraintLayout，具体参见： ConstraintSet Anadroid Api

zsn

zsn

ConstraintLayout笔记