android ConstraintLayout 约束布局
属性介绍
相对位置 Relative positioning
layout_constraintLeft_toLeftOf
layout_constraintLeft_toRightOf
layout_constraintRight_toLeftOf
layout_constraintRight_toRightOf
layout_constraintTop_toTopOf
layout_constraintTop_toBottomOf
layout_constraintBottom_toTopOf
layout_constraintBottom_toBottomOf
layout_constraintBaseline_toBaselineOf
layout_constraintStart_toEndOf
layout_constraintStart_toStartOf
layout_constraintEnd_toStartOf
layout_constraintEnd_toEndOf
如：
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintRight_toRightOf="@+id/secondTag"
该组件的右边与设置值id的右边对齐
间距 Margins
android:layout_marginStart
android:layout_marginEnd
android:layout_marginLeft
android:layout_marginTop
android:layout_marginRight
android:layout_marginBottom
注意只能设值正值或0
layout_goneMarginStart
layout_goneMarginEnd
layout_goneMarginLeft
layout_goneMarginTop
layout_goneMarginRight
layout_goneMarginBottom
当约束id组件gone时的间距
同样负值也无效
偏移 Centering positioning
layout_constraintHorizontal_bias
layout_constraintVertical_bias
如以下代码
app:layout_constraintHorizontal_bias="0.2"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintLeft_toRightOf="@+id/secondTag"
在左右方向都设置约束时 左右相对的间距百分比，默认为0.5
app:layout_constraintHorizontal_bias="0.3"则左边间距占0.3 右边间距0.7
Paste_Image.png
可见性对布局的影响 Visibility behavior
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/constraintLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<ImageView
android:id="@+id/iv1"
android:layout_width="0dp"
android:layout_height="100dp"
android:background="@color/colorPrimaryDark"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.0"
tools:layout_editor_absoluteX="24dp" />
<ImageView
android:id="@+id/iv2"
android:layout_width="0dp"
android:layout_height="200dp"
android:background="@color/colorAccent"
app:layout_constraintLeft_toLeftOf="parent"
android:visibility="gone"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/iv1" />
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:background="@color/colorPrimary"
android:contentDescription="@null"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/iv2"
tools:layout_editor_absoluteX="0dp" />
</android.support.constraint.ConstraintLayout>
Paste_Image.png
第二个view的约束关系还在，只是尺寸都是0,0了。
若其设置了margin，不会显示margin位置
尺寸约束 Dimension constraints
android:minWidth
android:layout_width
可设置的值
1、具体的数值 2dp
2、wrap_content
3、0dp 或match_parent
app:layout_constraintDimensionRatio="2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
layout_constraintDimensionRatio，width或height中有0dp时，该方向的尺寸以另一方向为基准按此比例计算，
bias是设置的是间距边距
取值可以为
1、a float value, representing a ratio between width and height 如 0.3、 2
2、a ratio in the form "width:height" 如：1:2 、2:1
如本例指宽为高的2倍
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
android:id="@+id/constraintLayout"
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:background="@color/colorAccent"
app:layout_constraintBottom_toBottomOf="@+id/constraintLayout"
app:layout_constraintLeft_toLeftOf="@+id/constraintLayout"
app:layout_constraintRight_toRightOf="@+id/constraintLayout"
app:layout_constraintTop_toTopOf="@+id/constraintLayout"
app:layout_constraintVertical_bias="0.0"/>
<ImageView
android:layout_width="0dp"
android:layout_height="200dp"
android:background="@color/colorAccent"
android:contentDescription="@null"
app:layout_constraintVertical_bias="0.2"
app:layout_constraintBottom_toBottomOf="@+id/constraintLayout"
app:layout_constraintDimensionRatio="4:5"
app:layout_constraintLeft_toLeftOf="@+id/constraintLayout"
app:layout_constraintRight_toRightOf="@+id/constraintLayout"
/>
</android.support.constraint.ConstraintLayout>
效果图
1、ImageView1处在顶部是因为app:layout_constraintVertical_bias="0.0"的作用
2、ImageView2 高是精确值 所以计算宽度就依高度为基准，
此时的app:layout_constraintVertical_bias是无意义的，因为是0dp
为何会居中自已理解吧
Paste_Image.png
Paste_Image.png
宽高都为0的情况
<Button android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintDimensionRatio="H,16:9"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
will set the height of the button following a 16:9 ratio, while the width of the button will match the constraints to parent
Paste_Image.png
constraintDimensionRatio中的 W or H 指后面比例的第1个是那个方向的
Chains
layout_constraintVertical_chainStyle
layout_constraintHorizontal_chainStyle
layout_constraintHorizontal_weight
layout_constraintVertical_weight
还没研究明白
When setting the attribute layout_constraintHorizontal_chainStyle
or layout_constraintVertical_chainStyle
on the first element of a chain, the behavior of the chain will change according to the specified style (default is CHAIN_SPREAD
).
CHAIN_SPREAD
-- the elements will be spread out (default style)
Weighted chain -- in CHAIN_SPREAD
mode, if some widgets are set to MATCH_CONSTRAINT
, they will split the available space
CHAIN_SPREAD_INSIDE
-- similar, but the endpoints of the chain will not be spread out
CHAIN_PACKED
-- the elements of the chain will be packed together. The horizontal or vertical bias attribute of the child will then affect the positioning of the packed elements
Fig. 10 - Chains Styles
引导线(Guideline) Virtual Helpers objects
public class Guideline extends View {
public Guideline(Context context) {
super(context);
super.setVisibility(8);
}
只是个不可见的组件，可用于提供约束，
