this is my code snippet and how to solve this error

Question

bottomNavigationBar: MotionTabBar( 
          labels: ["Account", "Home", "Dashboard"],
          initialSelectedTab: "Account",
          tabIconColor: Colors.green,
          tabSelectedColor: Colors.red,
          onTabItemSelected: (int value) {
            print(value);
            setState(() {
              _tabController.index = value;
            });
          },
          icons: [Icons.account_box, Icons.home, Icons.menu],
          textStyle: TextStyle(color: Colors.red),
        ),
        body: MotionTabBarView(
          controller: _tabController,
          children: <Widget>[
            SizedBox(
              height: 100,
              child: Center(
                child: Text("Account"),
              ),
            ),
            SizedBox(
              height: 100,
              child: Center(
                child: Text("Home"),
              ),
            ),
            SizedBox(
              height: 100,
              child: Center(
                child: Text("Dashboard"),
              ),
            ),
          ],
        )

Answer 1

Did you initialize _tabController in your initState method. Like this:

@override
void initState() {
  super.initState();
  _tabController = new MotionTabController(initialIndex:1,vsync: this);
}