[android help] I have a activity with theme Dialog,but in an activitygroup class it did not visible

which my problem is similar to this one: Android: Dialog themed activity not visible but I haven't see anyone answer it.

here is my code:

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public class QueryAct extends Activity implements OnFocusChangeListener ,          OnItemClickListener , OnResponseListener , OnStartListener

{ oncreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mAct = this ; setContentView(R.layout.activity_query) ; views = new QueryActViews(mAct) ; searchThread = new SearchThread() ; searchThread.responseListener = this ; searchThread.startListener = this ; intialViews(views) ;

    HUtil.checkAppUpdate(this);
}

}

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and here is the method in class HUtil

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public static void checkAppUpdate(Context ctx)
{
SharedPreferences sp = ctx.getSharedPreferences(GContst.SP_NAME, Context.MODE_PRIVATE);

boolean not_alarm_update = sp.getBoolean(GContst.NOT_ALARM_UPDATE, false);

    if(!not_alarm_update)
    {
        String update_url = sp.getString(GContst.UPDATE_URL, "");
        if(!"".equals(update_url))
        {
            ctx.startActivity(new Intent(ctx,UpdateDialog.class));
        }
    }
}
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and this is my manifest.xml I just set the activity updateDialog's theme like this:

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        android:name=".UpdateDialog"
        android:launchMode="singleInstance"
        android:theme="@android:style/Theme.Dialog" />
enter code here

.

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