How I can set keep screen on and full screen flag?

fullscreen in my app and I write this code :

  public void onCreate(Bundle savedInstanceState) {
         requestWindowFeature(Window.FEATURE_NO_TITLE);
         setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
           getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                    WindowManager.LayoutParams.FLAG_FULLSCREEN); 
               super.onCreate(savedInstanceState); 
        setContentView(R.layout.main);
                       .
                       .
                       .

And keep screen on in my app I write this code in layout :

android:keepScreenOn="true" 

Although it is not always , sometimes error me like this:

java.lang.IllegalArgumentException: View not attached to window manager
at android.view.WindowManagerImpl.findViewLocked(WindowManagerImpl.java:381)
at android.view.WindowManagerImpl.removeView(WindowManagerImpl.java:226)
at android.view.Window$LocalWindowManager.removeView(Window.java:432)
at android.app.Dialog.dismissDialog(Dialog.java:278)
at android.app.Dialog.access$000(Dialog.java:71)
at android.app.Dialog$1.run(Dialog.java:111)
at android.app.Dialog.dismiss(Dialog.java:268)
at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:3691)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:847)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:605)
at dalvik.system.NativeStart.main(Native Method)

What can I do? I write true code? THANKS...

super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.main);

super.onCreate must be called first....

You can do it programatically:

public class ActivityName extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // remove title
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);
        setContentView(R.layout.main);
    }
}

Or you can do it via your AndroidManifest.xml file:

<activity android:name=".ActivityName"
    android:label="@string/app_name"
    android:theme="@android:style/Theme.NoTitleBar.Fullscreen">
</activity>