Many thanks to gskinner for "The vignettes" showcase presented at Flutter Interact '19 : They created an awesome creative experience and most of the code in this package comes from their realisation. I was really impressed by their huge work but the code, even if it was open-sourced, was not usable as it. So I did some refactoring for maintainability, I extracted some fields to be able to adapt and skin the widget according to our design and decided to share it.

Enjoy

FluidNavBar is simply a bottom navigation bar but with a very cool and fluid effect while animating the transition between an active button to another one.

The example below shows you the minimal code to use the widget.

@override
  Widget build(context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: Color(0xFF75B7E1),
        extendBody: true,
        body: _theBody,
        bottomNavigationBar: FluidNavBar(                     // (1)
          icons: [                                            // (2)
            FluidNavBarIcon(svgPath: "assets/home.svg"),      // (3)
            FluidNavBarIcon(svgPath: "assets/bookmark.svg"),
          ],
          onChange: _handleNavigationChange,                  // (4)
        ),
      ),
    );
  }

(1) Create an instance of FluidNavBar
(2) Set the icons, of type FluidNavBarIcon, to display in the navigation bar
(3) FluidNavBarIcon supports SVG asset or IconData
(4) Set the callback to react when the user tap an icon (the callback parameter contains the icon's index)

When defining FluidNavBarIcon you can provide an SVG asset or an IconData. Use the field svgPath for an SVG or the field icon for an IconData.

Example:

FluidNavBar(
          icons: [
            FluidNavBarIcon(
                svgPath: "assets/home.svg",
                backgroundColor: Color(0xFF4285F4),
                extras: {"label": "home"}),
            FluidNavBarIcon(
                icon: Icons.bookmark_border,
                backgroundColor: Color(0xFFEC4134),
                extras: {"label": "bookmark"}),
          ],

Note: For backward compatibility (previous to v1.2.0) you can still use the field iconPath to set the SVG asset to use (this is the same behaviour of svgPath). But this field has been deprecated and will be removed in a future version.

FluidNavBar comes with a default set of styles which are directly inherited from the gskinner showcase. You can override different properties to adapt the fluid navigation bar to your current design:

• the bar background color (Colors.white by default)
• the icon background color (the same color as the bar background color by default)
• the icon foreground color when it's selected (Colors.black by default)
• the icon foreground color when it's unselected (Colors.grey by default)

The easiest way is to define one or more properties in a FluidNavBatStyle and set this instance in the style property of the FluidNavBar:

FluidNavBar(
  icons: [
    FluidNavBarIcon(svgPath: "assets/home.svg"),
    FluidNavBarIcon(svgPath: "assets/bookmark.svg"),
  ],
  onChange: _handleNavigationChange,
  style: FluidNavBarStyle(
    barBackgroundColor: Color(0xFFFB5C66),
    iconBackgroundColor: Colors.white,
    iconSelectedForegroundColor: Color(0xFFFB5C66),
    iconUnselectedForegroundColor: Colors.black
  ),
)

is displayed as:

Properties:

You can also define some specific styles per icon, by using optional parameters of FluidNavBarIcon:

FluidNavBar(
  icons: [
    FluidNavBarIcon(svgPath: "assets/home.svg", backgroundColor: Color(0xFF4285F4)),
    FluidNavBarIcon(svgPath: "assets/bookmark.svg", backgroundColor: Color(0xFFEC4134)),
    FluidNavBarIcon(svgPath: "assets/partner.svg", backgroundColor: Color(0xFFFCBA02)),
    FluidNavBarIcon(svgPath: "assets/conference.svg", backgroundColor: Color(0xFF34A950)),
  ],
  onChange: _handleNavigationChange,
  style: FluidNavBarStyle(
    iconUnselectedForegroundColor: Colors.white
  )
),

is displayed as

Note: In this example I used also a global style for the foreground color of unselected icons, as I don't want to set the same color for all icons

Properties:

You can define global styles, local styles, both or no style at all!

To define the proper style to apply it tries, for each style, to resolve its value in the following order:
1- local style
2- global style
3- default value
when a value is resolved then it applies it to the widget.

For example if you set the global style iconBackgroundColor to Colors.red and you also set the local style backgroundColor to Colors.green for an icon, then it will use the green color as the local style will be resolved before the global one.

There are also few options, you can play with. They are global options and accessible throw FluidNaBar fields.

For an animationFactor of 2.0 (slower) and a scaleFactor of 2.0 (a zoom-in bigger than the default one), the result is:

Feel free to create an issue if you find a bug or if you need new features. Of course PRs are welcome!

If you want to contact me on Twitter: @etaix

Many thanks to these contributors:

• Umair M
• Dmitriy Govorov
• Christos Tsortanidis
• Dorbmon