Application window transparency does not work in Android

I need a transparent MainWindow background for Android application. I have added android:theme="@android:style/Theme.Translucent" to <application...> section of AndroidManifest.xml. Even I added lines
MainWindow w;
w.setAttribute( Qt::WA_NoSystemBackground );
w.setAttribute( Qt::WA_TranslucentBackground );
w.setAttribute( Qt::WA_OpaquePaintEvent, false );
to main(). After application starts I can see underlaying application for very short time then it coveres by black background. I did not find how solve this. I strongly need transparent MainWindow background.