2 布局

1.LinearLayout—线性布局

<LinearLayout
         android:orientation="vertical"
         android:layout_width="match_parent"
         android:layout_height="match_parent">
         <Button
             android:text="按钮"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content" />
     </LinearLayout>

android:layout_width     //定义width
android:layout_height    //定义height
math_parent             //继承父组件的width、height
wrap_content           //组件实际的大小

1.1线性布局中可以嵌套

//两个并排显示
<LinearLayout
        android:background="#333"
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
       <LinearLayout
           android:background="#333"
           android:layout_weight="1"
           android:layout_width="0dp"
           android:layout_height="match_parent"></LinearLayout>
        <LinearLayout
            android:background="#fff"
            android:layout_weight="1"
            android:layout_width="0dp"
            android:layout_height="match_parent"></LinearLayout>
    </LinearLayout>

2.GridLayout

//一行四个
<GridLayout
        android:columnCount="4"
        android:rowCount="3"
        android:layout_width="match_parent"
        android:layout_height="300dp"
        tools:context="MissingConstraints"
        >
        <Button />
        <Button />
        <Button />
        <Button />
        <Button />
        <Button />
        <Button />
        <Button />
    </GridLayout>