让背景小图不是拉伸而是多个重复

<xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="@+id/MainLayout"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:background="@drawable/backrepeat"
>
<bitmap
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:src="@drawable/tile"
    android:tileMode="repeat"
    android:dither="true" />