3.App Resources-Resource Types/Layout Resource

<?xml version="1.0" encoding="utf-8"?>
<ViewGroup  //A container for other View elements
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@[+][package:]id/resource_name"
    android:layout_height=["dimension" | "fill_parent" | "wrap_content"]
    android:layout_width=["dimension" | "fill_parent" | "wrap_content"]
    [ViewGroup-specific attributes] >

    <View //An individual UI component, generally referred to as a "widget".
        android:id="@[+][package:]id/resource_name"
        android:layout_height=["dimension" | "fill_parent" | "wrap_content"]
        android:layout_width=["dimension" | "fill_parent" | "wrap_content"]
        [View-specific attributes] >
        <requestFocus/>//Any element representing a View object can include this empty element, which gives its parent initial focus on the screen. You can have only one of these elements per file.
    </View>

    <ViewGroup >
        <View />
    </ViewGroup>

    <include layout="@layout/layout_resource"/>

</ViewGroup>