看不明白了
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:background="@drawable/my_background"
android:orientation="vertical" >
<TextView
android:layout_height="wrap_content"
android:text="Welcome to my App"
android:textAppearance="?android:attr/textAppearanceLarge"
android:layout_width="wrap_content"
android:layout_margin="20dp" />
</LinearLayout>