[Solved] Flutter BottomNavigationBar not working with more than three items


Asked by Michael on September 06, 2018 (source).

I´ve a problem with the BottomNavigationBar in Flutter (0.6). As soon as I add more then three BottomNavigationBarItems as children, the buttons in the bar have white icons and they are messed up. When I use only three or less items, everything´s fine.

Here´s the widget code I use and which breaks the bar:

bottomNavigationBar: BottomNavigationBar(
          currentIndex: 0,
          iconSize: 20.0,
          items: [
              title: Text('Home'), icon: Icon(Icons.accessibility)),
              title: Text('Preise'), icon: Icon(Icons.account_box)),
              title: Text('Test'), icon: Icon(Icons.adb)),
              title: Text('Mehr'), icon: Icon(Icons.menu))

Has anybody an idea what´s wrong here?

Thanks in advance for any hint, Michael


Question answered by Günter Z (source).

For 4 or more items, set the type to fixed.

bottomNavigationBar: BottomNavigationBar(
  type: BottomNavigationBarType.fixed, // This is all you need!
  items: // ...,

From https://github.com/flutter/flutter/issues/13642#issuecomment-371875044

When more than 3 BottomNavigationBar items are provided the type, if unspecified, changes to BottomNavigationBarType.shifting per https://docs.flutter.io/flutter/material/BottomNavigationBar/BottomNavigationBar.html. This bit of information should be highlighted in the class's doc. It's easy to overlook where it is (I overlooked it).

When the BottomNavigationBar's type is BottomNavigationBarType.shifting the items text and icons are rendered in white, via DefaultTextStyle and IconTheme. It's assumed that theirBottomNavigationBarItem.backgroundColor will be specified as a contrasting color. This is obviously confusing.

The overall idea with shifting type bottom navigation bars is that each item will have a different background color (that contrasts with white), since that color will become the color of the entire navigation bar, when the item is selected.

The doc for BottomNavigationBar, and NavigationBarItem needs to be improved.