Android studio约束布局 ConstraintLayout

ConstraintLayout(约束布局), 是2016年Google I/O最新推出的Android布局, 目前还在完善阶段. 从推出的力度而言, 应该会成为主流布局样式. 在最新版本的Android Studio中, ConstraintLayout已经成为默认布局.

 

概念

 

ConstraintLayout约束布局的含义: 根据布局中的其他元素或视图, 确定View在屏幕中的位置. 包含三个重要信息, 根据其他视图设置位置, 根据父容器设置位置, 根据基准线设置位置.

layout_constraint[本源]_[目标]="[目标ID]"

例如:

app:layout_constraintBottom_toBottomOf="@+id/constraintLayout"

约束当前View的底部至目标View的底部, 目标View是constraintLayout. 表明, 把当前View放置到constraintLayout(父容器)的底部, 并且底部一致.

为了演示多个示例, 使用复用的Activity页面. 根据参数设置标题和布局Id.

public  class  LayoutDisplayActivity  extends  AppCompatActivity {
    private  static  final  String TAG = LayoutDisplayActivity. class .getSimpleName();
    static  final  String EXTRA_LAYOUT_ID = TAG +  ".layoutId" ;  // 布局ID

    @Override  protected  void  onCreate( @Nullable  Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setTitle(getIntent().getStringExtra(Intent.EXTRA_TITLE));
        final  int  layoutId = getIntent().getIntExtra(EXTRA_LAYOUT_ID,  0 );
        setContentView(layoutId);  // 设置页面布局, 复用布局
    }
}

主页面使用ListView展示多个项, 每项都是不同的布局. 点击项发送不同的Intent, 填充所要显示的页面.

public  class  MainActivity  extends  AppCompatActivity {
    @Override
    protected  void  onCreate(Bundle savedInstanceState) {
        super .onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ListView list = (ListView) findViewById(R.id.activity_main);
        ArrayAdapter adapter =  new  ArrayAdapter<>( this ,
                android.R.layout.simple_list_item_1, LIST_ITEMS);
        list.setAdapter(adapter);
        list.setOnItemClickListener( new  AdapterView.OnItemClickListener() {
            @Override
            public  void  onItemClick(AdapterView adapterView, View view,  int  i,  long  l) {
                // 复用显示布局
                Intent intent =  new  Intent(MainActivity. this , LayoutDisplayActivity. class );
                intent.putExtra(Intent.EXTRA_TITLE, LIST_ITEMS[i]);  // 标题
                intent.putExtra(LayoutDisplayActivity.EXTRA_LAYOUT_ID, LAYOUT_IDS[i]);  // 布局Id
                startActivity(intent);
            }
        });
    }
}

基础

ConstraintLayout布局最基本的使用方式, 就是直接指定位置. 取消按钮的底部对齐constraintLayout(父容器)的底部, 左侧对齐父容器的左侧. 下一步按钮的底部对齐父容器的底部, 而左侧对齐取消按钮的右侧. 并且每个按钮边缘有Margin空隙.

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"
                                             android:id = "@+id/constraintLayout"
                                             android:layout_width = "match_parent"
                                             android:layout_height = "match_parent" >

    < Button
        android:id = "@+id/cancel_button"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:layout_marginBottom = "16dp"
        android:layout_marginStart = "16dp"
        android:text = "取消"
        app:layout_constraintBottom_toBottomOf = "@id/constraintLayout"
        app:layout_constraintStart_toStartOf = "@id/constraintLayout" />

    < Button
        android:id = "@+id/next_button"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:layout_marginBottom = "16dp"
        android:layout_marginStart = "16dp"
        android:text = "下一步"
        app:layout_constraintBottom_toBottomOf = "@id/constraintLayout"
        app:layout_constraintStart_toEndOf = "@id/cancel_button" />

android.support.constraint.ConstraintLayout >

ConstraintLayout的属性设置, 最重要的就是理解属性的表示含义.

Base

比例

ConstraintLayout布局除了对齐属性, 还有重要的比例属性. 中心(Center)按钮需要把全部边界与constraintLayout(父容器)边界对齐, 则为居中. 同时还可以设置水平与竖直的比例, 如0.25. Bias按钮设置水平与竖直的比例是0.25, 表示左侧与右侧比例是1:4, 上部与下部的比例是1:4.

constraintHorizontal_bias设置水平比例, constraintVertical_bias设置竖直比例.

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" >

    < Button
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "Center"
        app:layout_constraintBottom_toBottomOf = "@+id/constraintLayout"
        app:layout_constraintEnd_toEndOf = "@id/constraintLayout"
        app:layout_constraintStart_toStartOf = "@id/constraintLayout"
        app:layout_constraintTop_toTopOf = "@+id/constraintLayout" />

    < Button
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "Bias"
        app:layout_constraintBottom_toBottomOf = "@+id/constraintLayout"
        app:layout_constraintEnd_toEndOf = "@id/constraintLayout"
        app:layout_constraintHorizontal_bias = "0.25"
        app:layout_constraintStart_toStartOf = "@id/constraintLayout"
        app:layout_constraintTop_toTopOf = "@+id/constraintLayout"
        app:layout_constraintVertical_bias = "0.25" />

android.support.constraint.ConstraintLayout >


tools:layout_editor_absoluteX属性对于视图起到辅助作用, 理解边界的真实距离, 点击可视化布局会自动生成.

Bias

引导线

ConstraintLayout布局除了与布局对齐以外, 还可以与引导线(Guideline)对齐. 设置竖直引导线(Guideline)距离左侧72dp. 按钮(Button)的左侧都与引导线对齐, 上下使用比例的方式排列, 一个0.25比例, 一个0.75比例.

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.support.constraint.Guideline
        android:id = "@+id/guideLine"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:orientation = "vertical"
        app:layout_constraintGuide_begin = "72dp" />

    < Button
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "Guide Up"
        app:layout_constraintBottom_toBottomOf = "@+id/constraintLayout"
        app:layout_constraintStart_toStartOf = "@id/guideLine"
        app:layout_constraintTop_toTopOf = "@+id/constraintLayout"
        app:layout_constraintVertical_bias = "0.25" />

    < Button
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "Guide Down"
        app:layout_constraintBottom_toBottomOf = "@+id/constraintLayout"
        app:layout_constraintStart_toStartOf = "@id/guideLine"
        app:layout_constraintTop_toTopOf = "@+id/constraintLayout"
        app:layout_constraintVertical_bias = "0.75" />

android.support.constraint.ConstraintLayout >

Guide Line

视图尺寸

ConstraintLayout布局中的控件也可以设置填充尺寸. 控件把宽度设置为0dp会自动根据位置进行填充. 如Large按钮, 左侧对齐与Small按钮的左侧, 右侧对齐与constraintLayout父控件的右侧, 宽度设置为0dp, 实际会填充全部位置.

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"
                                             android:id = "@+id/constraintLayout"
                                             android:layout_width = "match_parent"
                                             android:layout_height = "match_parent" >

    < Button
        android:id = "@+id/small"
        android:layout_width = "wrap_content"
        android:layout_height = "wrap_content"
        android:text = "Small"
        app:layout_constraintStart_toStartOf = "@id/constraintLayout"
        app:layout_constraintTop_toTopOf = "@id/constraintLayout" />

    < Button
        android:layout_width = "0dp"
        android:layout_height = "wrap_content"
        android:text = "Large"
        app:layout_constraintBottom_toBottomOf = "@id/constraintLayout"
        app:layout_constraintEnd_toEndOf = "@id/constraintLayout"
        app:layout_constraintStart_toEndOf = "@id/small"
        app:layout_constraintTop_toTopOf = "@id/constraintLayout" />

android.support.constraint.ConstraintLayout >

Measure

视图纵横比

ConstraintLayout布局还可以使用constraintDimensionRatio设置视图的纵横比, 则需要把宽(layout_width)或者高(layout_height)设置为0dp, 根据另一个属性和比例, 计算当前属性, 如两个图片控件的显示大小.

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"
                                             android:id = "@+id/constraintLayout"
                                             android:layout_width = "match_parent"
                                             android:layout_height = "match_parent" >

    < ImageView
        android:layout_width = "0dp"
        android:layout_height = "200dp"
        android:background = "@color/colorAccent"
        android:src = "@drawable/total_large"
        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"
        android:src = "@drawable/total_large"
        app:layout_constraintBottom_toBottomOf = "@+id/constraintLayout"
        app:layout_constraintDimensionRatio = "4:3"
        app:layout_constraintLeft_toLeftOf = "@+id/constraintLayout"
        app:layout_constraintRight_toRightOf = "@+id/constraintLayout" />

android.support.constraint.ConstraintLayout >

Ratio

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ConstraintLayout约束布局的基本使用方式就是这些, 可以观察到ConstraintLayout布局兼顾LinearLayout与RelativeLayout的优点, 非常适合构建复杂布局, 会成为Android的主流布局方式.