Android : Unable to find chromecast devices in a reliable manner

This is my first question in stackoverflow. So please be patient with me...

I want to start an activity which detects all chromecast device in my WLAN.

First of all I implement an own activity extending Activity.

The onCreate()-Method looks like this:

protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main_cast);

    try
    {
        // get the parameters from intent
        Bundle extras = getIntent().getExtras();
        if (extras == null) 
        {
            // this is just for testing purposes --> set a sample directory name
            ms_ImageBasePath = "/storage/extSdCard/Bilder/2014/2014_08/2014_08_09";
            ms_ImageFilename = "";
        }
        else
        {
            // get the data from the calling activity
            ms_ImageBasePath = extras.getString(FWCastActivity.IMAGEPATH2CAST);
            ms_ImageFilename = extras.getString(FWCastActivity.IMAGE2CAST);
        }

        // create the controls
        mo_Button_left = (ImageButton)this.findViewById(R.id.cast_left_imageButton);
        mo_Button_right = (ImageButton)this.findViewById(R.id.cast_right_imageButton);
        mo_Button_stop = (ImageButton)this.findViewById(R.id.cast_stop_imageButton);
        mo_SelectDeviceButton = (ImageButton)findViewById(R.id.cast_select_device_imageButton);
        mo_SelectDeviceButton.setBackgroundColor(Color.WHITE);
        mo_Filename = (TextView)findViewById(R.id.cast_filename_textView);
        mo_Filename.setText("-");
        mo_Headline = (TextView)findViewById(R.id.cast_headline_textView);
        mo_ImageView = (ImageView)findViewById(R.id.cast_currentview_imageView);

        // prepare the spinner which collects the routes
        mo_CastDeviceSpinner = (Spinner) findViewById(R.id.cast_device_selection_spinner);
        updateAdapter();


        // prepare all the images for casting
        if (prepareImages()==false)
        {
            // an error happened
            throw new Exception("No images found in " + ms_ImageBasePath + " to cast");
        }

        // get the ip address --> important for casting images 
        ms_IPAddress = getLocalIpv4Address();

        // create the handlers for the controls
        createHandler();

        // create the webserver which servers the images to chromecast
        createWebServer(ms_ImageBasePath);

        // create the mediarouter --> this starts searching for available devices
        createMediaRouter();


    }
    catch (Exception e)
    {
        // problem in onCreate
        doLog("Exception in onCreate: " + e.toString());
        // to do: make sure process stops here...
    }
}

The createMediaRouter()-method looks like this:

private void createMediaRouter()
{
    try
    {
        mMediaRouter = MediaRouter.getInstance(getApplicationContext());

        // Create a MediaRouteSelector for the type of routes your app supports
        //mMediaRouteSelector = new MediaRouteSelector.Builder().addControlCategory(CastMediaControlIntent.categoryForCast(CastMediaControlIntent.DEFAULT_MEDIA_RECEIVER_APPLICATION_ID)).build();
        mMediaRouteSelector = new MediaRouteSelector.Builder().addControlCategory(CastMediaControlIntent.categoryForCast(APPID)).build();

        // Create a MediaRouter callback for discovery events
        mMediaRouterCallback = new CastFWMediaRouterCallback();

    }
    catch (Exception e)
    {
        doLog("Exception in createMediaRouter: " + e.toString());
    }
}

The callback class looks like this:

private class CastFWMediaRouterCallback extends MediaRouter.Callback 
{

    @Override
    public void onRouteAdded(MediaRouter router, MediaRouter.RouteInfo info) 
    {
        try
        {
            doLog("onRouteAdded: info.getName = " + info.getName());
            // Add route to list of discovered routes
            synchronized (this) 
            {
                mRouteInfos.add(info);
                mRouteNames.add(info.getName() + " (" + info.getDescription()+ ")");

                updateAdapter();

                doLog(" --> Found route: Now you can select route from list and start casting");
            }
        }
        catch (Exception e)
        {
            doLog("Ex in MyMediaRouterCallback.onRouteAdded: " + e.toString());
        }
    }

    @Override
    public void onRouteRemoved(MediaRouter router, MediaRouter.RouteInfo info) 
    {
        try
        {

            doLog("onRouteRemoved: info=" + info);
            // Remove route from list of routes
            synchronized (this) 
            {
                for (int i = 0; i < mRouteInfos.size(); i++) {
                    MediaRouter.RouteInfo routeInfo = mRouteInfos.get(i);
                    if (routeInfo.equals(info)) 
                    {
                        mRouteInfos.remove(i);
                        mRouteNames.remove(i);
                        updateAdapter();
                        return;
                    }
                }
            }
        }
        catch (Exception e)
        {
            doLog("Ex in MyMediaRouterCallback.onRouteRemoved: " + e.toString());
        }   
    }

    @Override
    public void onRouteSelected(MediaRouter router, RouteInfo info) 
    {
        try
        {

            doLog("onRouteSelected: info=" + info.getName());
            mSelectedDevice = CastDevice.getFromBundle(info.getExtras());
            String routeId = info.getId();
            doLog("route with id " + routeId + " selected --> now preparing API Client");
            prepareApiClient();

        }
        catch (Exception e)
        {
            doLog("Exception in MyMediaRouterCallback.onRouteSelected: " + e.toString());
        }   
    }

    @Override
    public void onRouteUnselected(MediaRouter router, RouteInfo info) {
        doLog("onRouteUnselected: info=" + info);
        teardown();
        mSelectedDevice = null;
    }

} // end of inner class

The callback-class is added in the onResume-method

@Override
protected void onResume() 
{
    super.onResume();
    if (mMediaRouter!=null)
    {
        // Add the callback to start device discovery
        mMediaRouter.addCallback(mMediaRouteSelector, mMediaRouterCallback,MediaRouter.CALLBACK_FLAG_REQUEST_DISCOVERY);

    }
}

This code works properly for the first time I use it. It starts, my chromecast device is detected and I can send image-links on my smartphone over an integrated webserver. Images are shown on the chromecast device -great. If I finish the activity and create it again, the routes are not found again.

I've already discussed things on Google+ but the guys there told me to post my code on StackOverflow. It would be great to get some help. I'd also appreciate a piece of code where the chromecast devices are detected manually.

Any help appreciated! Thanks!