MediaRouter android programming

Question

I have a problem with MediaRouter for an android application,i followed the android API guide for MediaRouter but when i run the application,on toolbar doesn't appear any button.

public class MediaRouterPlaybackActivity extends AppCompatActivity {
    private MediaRouteSelector mSelector;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.miracast);
        Toolbar myToolbar = (Toolbar) findViewById(R.id.my_toolbar);
        setSupportActionBar(myToolbar);
        // Create a route selector for the type of routes your app supports.
        mSelector = new MediaRouteSelector.Builder()
                // These are the framework-supported intents
                .addControlCategory(MediaControlIntent.CATEGORY_REMOTE_PLAYBACK)
                .build();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu){
        super.onCreateOptionsMenu(menu);
        // Inflate the menu and configure the media router action provider.
        getMenuInflater().inflate(R.menu.mediarouter, menu);
        // Attach the MediaRouteSelector to the menu item
        MenuItem mediaRouteMenuItem = menu.findItem(R.id.media_route_menu_item);
        MediaRouteActionProvider mediaRouteActionProvider =
                (MediaRouteActionProvider) MenuItemCompat.getActionProvider(
                        mediaRouteMenuItem);
        // Attach the MediaRouteSelector that you built in onCreate()
        mediaRouteActionProvider.setRouteSelector(mSelector);
        // Return true to show the menu.
        return true;
    }
}

This is the code of toolbar:

<android.support.v7.widget.Toolbar
        android:id="@+id/my_toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="#4696e5"
        android:elevation="4dp"
        android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
        app:popupTheme="@style/Theme.AppCompat"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="60dp" />

Answer 1

I had the same problem. In my case it was becasue the button is only shown if there is some media receiver detected such as Chromecast or a custom media route. If you don't have any device to send the button doesn't show.