的manifest.xml

<activity
    android:name="com.yourapp.app"
    android:label="@string/app_name"
    android:screenOrientation="landscape"
    android:theme="@style/Theme.YourTheme"
    ...
</activity>

RES /价值/ styles.xml

<style name="YourTheme" parent="android:Theme.Light">
    ...
</style>