dartTabDrag

class _MyAppState extends State<MyApp> with TickerProviderStateMixin {
  static int _noOfTabs = 0;
  static List<Widget> _tabList;
  static List<Widget> _tabViewList;

  TabController _controller;

  @override
  void initState() {
    super.initState();
   // buttonPressed();
  }

  @override
  void dispose() {
    _controller.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: new AppBar(
          title: Text('TabBar Preview'),
          bottom: (_noOfTabs > 0)
              ? PreferredSize(
                  child: Draggable(
                    child: TabBar(
                        controller: _controller,
                        isScrollable: true,
                        tabs: _tabList),
                    feedback: Container(),
                    onDragStarted: () {
                      print("stareted");
                    },
                    onDragCompleted: () {
                      print("completed");
                    },
                    onDragEnd: (dragDetails){

                      print(dragDetails.velocity.pixelsPerSecond.direction);
                      print(dragDetails.velocity.pixelsPerSecond.distance);


                      if(dragDetails.velocity.pixelsPerSecond.distance > 0.5){

                        int index = _controller.index;

                        if(dragDetails.velocity.pixelsPerSecond.direction < 0 && index <_tabList.length+1){ //Right, figure out how much better for you

                          Widget tabViewTemp = _tabViewList[index+1];
                          _tabViewList[index+1] = _tabViewList[index];
                          _tabViewList[index] = tabViewTemp;

                          Widget tabText = _tabList[index+1];
                          _tabList[index+1] = _tabList[index];
                          _tabList[index] = tabText;

                        } else if(index > 0){ //left

                          Widget tabViewTemp = _tabViewList[index-1];
                          _tabViewList[index-1] = _tabViewList[index];
                          _tabViewList[index] = tabViewTemp;

                          Widget tabText = _tabList[index-1];
                          _tabList[index-1] = _tabList[index];
                          _tabList[index] = tabText;

                        }

                          _controller = TabController(length: _noOfTabs, vsync: this);
                          _controller.animateTo(index+1);

                          setState(() {

                          });

                      }
                    },

                  ),
                 preferredSize: Size(double.infinity, 24.0),
                )
              : null,
        ),
        body:  (_noOfTabs > 0)
              ? TabBarView(
                  controller: _controller,
                  children: _tabViewList,
                )
              : Center(
                  child: Text('No tabs'),
                ),

        floatingActionButton: FloatingActionButton(
            child: Icon(Icons.add), onPressed: buttonPressed),
      ),
    );
  }

  void buttonPressed() {
    setState(() {
      _noOfTabs++;
    });

    _tabList = new List<Widget>();
    _tabViewList = new List<Widget>();

    for (var i = 0; i < _noOfTabs; i++) {
      _tabList.add(Tab(text: 'Tab ' + (i + 1).toString()));
      _tabViewList.add(Center(child: Text('Tab ' + (i + 1).toString())));
    }

    _controller = TabController(length: _noOfTabs, vsync: this);
    _controller.animateTo(_noOfTabs - 1);
  }
}