title: bottom navigation bar transition in flutter
body: <p>Is it possible to change the transition of routing in items of a bottomNavigationBar?
  my mean is when you tap any of items in bottomNavigationBar , then the body change with nice animation like custom animation.
  for example with:</p>
  
  <pre class="lang-dart prettyprint-override"><code>class MyCustomRoute&lt;T&gt; extends MaterialPageRoute&lt;T&gt; {
    MyCustomRoute({ WidgetBuilder builder, RouteSettings settings })
        : super(builder: builder, settings: settings);
  
    @override
    Widget buildTransitions(BuildContext context,
        Animation&lt;double&gt; animation,
        Animation&lt;double&gt; secondaryAnimation,
        Widget child) {
      if (settings.isInitialRoute)
        return child;
      return new FadeTransition(opacity: animation, child: child);
    }
  }
  </code></pre>