Need help,Screen didn't turn on after I change Activity's theme

I'm making my alarm app. There is an Activity to show alarm infomation. I want turn on the screen and unlock it. I wrote these code

AlarmActivity.java:

public class AlarmActivity extends Activity {
  ......
  void onCreate(Bundle bl) {
    .....
    final Window win = getWindow();
    win.requestFeature(android.view.Window.FEATURE_NO_TITLE);   
    win.addFlags(WindowManager.LayoutParams.FLAG_SHOW_WHEN_LOCKED
               | WindowManager.LayoutParams.FLAG_DISMISS_KEYGUARD
               | WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON
               | WindowManager.LayoutParams.FLAG_TURN_SCREEN_ON);

    LayoutInflater inflater = LayoutInflater.from(this);
    setContentView(inflater.inflate(R.layout.alarm, null));
  }

  ......
}  

AndroidManifest.xml

{activity android:name="AlarmTaskActivity"
                android:excludeFromRecents="true"
                android:theme="@android:style/Theme.Wallpaper.NoTitleBar"
                android:launchMode="singleInstance"
                android:taskAffinity=""
                android:configChanges="orientation|keyboar开发者_JS百科dHidden|keyboard|navigation"/}

It's ok,but when I change

android:theme="@android:style/Theme.Wallpaper.NoTitleBar" to android:theme="@android:style/Theme.Dialog" the screen did not turn on nor unlock, I am really confused....

Can you please tell me how to make the screen turn on and unlock when I use "@android:style/Theme.Dialog"?

Thanks

by the way,I have android 2.0 in my test device.

In order to activate the screen and force it to stay on, you need to use a WakeLock. See the documentation for more information. Changing the theme along won't cause the screen to wake up. You'll need to use the ACQUIRE_CAUSES_WAKEUP flag in order to do that.