让Android程序单例运作

<?xmlxxxx?><manifestxxxxxxx>    <applicationandroid:icon="@drawable/icon"          android:label="@string/app_name"        android:launchMode="singleInstance">    <activityandroid:name=".Main"          android:label="Main Window"          android:icon="@drawable/icon>        <intent-filter>            <actionandroid:name="android.intent.action.MAIN"/>            <categoryandroid:name="android.intent.category.LAUNCHER"/>        </intent-filter>      <activityxxxxxxxxx/></manifest>