如何在Android 2.2上切换到真正的全屏显示？

getWindow().setFlags(LayoutParams.FLAG_FULLSCREEN, LayoutParams.FLAG_FULLSCREEN);

public class HellofullActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.main);
    }
}