Flutter中我底部导航栏中的添加索引问题

Question

”“我需要如何解决底部导航栏中的添加索引以导航到我的应用程序的问题，我看到的底部导航条码与Flutter Material成比例，但是找不到在我的应用中添加索引的方法代码，这就是我的代码：“

这里是代码要求的索引，但是不起作用

  

那是我的代码

import 'package:flutter/material.dart';

class MyBottomNavigationBar extends StatefulWidget{

  final List<BottomNavigationDotBarItem> items;
  final Color activeColor;
  final Color color;
  BottomNavigationDotBar(
      {@required this.items,
        this.onItemSelected, 
        this.activeColor, 
        this.color,
        Key key}): super(key: key);
  @override
  State<StatefulWidget> createState() => _MyBottomNavigationBarState();

}

class _MyBottomNavigationBarState extends State<MyBottomNavigationBar>{
  int currentIndex;
  GlobalKey _keyBottomBar = GlobalKey();
  double _numPositionBase, _numDifferenceBase, _positionLeftIndicatorDot;
  int _indexPageSelected = 0;
  Color _color, _activeColor;

  @override
  void didUpdateWidget( oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.currentIndex != widget.currentIndex) {
      final newPosition = widget.currentIndex / _numPositionBase;
    }
  }



  @override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback(_afterLayout);
    super.initState();
  }

  @override
  void dispose() {
    super.dispose();
  }

  _afterLayout(_) {
    _color = widget.color ?? Colors.black45;
    _activeColor = widget.activeColor ?? Theme.of(context).primaryColor;
    final sizeBottomBar = (_keyBottomBar.currentContext.findRenderObject() as RenderBox).size;
    _numPositionBase = ((sizeBottomBar.width / widget.items.length));
    _numDifferenceBase = (_numPositionBase - (_numPositionBase / 2) + 2);
    setState(() { _positionLeftIndicatorDot = _numPositionBase - _numDifferenceBase; });
  }

  @override
  Widget build(BuildContext context) => Container (
    padding: EdgeInsets.fromLTRB(5, 0, 5, 5),
    child: Material(
        elevation: 5,
        borderRadius: BorderRadius.circular(10),
        child: Container(
          padding: EdgeInsets.symmetric(vertical: 12),
          child: Stack(
            key: _keyBottomBar,
            children: <Widget>[
              Padding(
                padding: EdgeInsets.only(bottom: 12),
                child: Row(
                    mainAxisAlignment: MainAxisAlignment.spaceAround,
                    children: _createNavigationIconButtonList(widget.items.asMap())
                ),
              ),
              AnimatedPositioned(
                  child: CircleAvatar(radius: 2.5, backgroundColor: _activeColor),
                  duration: Duration(milliseconds: 400),
                  curve: Curves.fastOutSlowIn,
                  left: _positionLeftIndicatorDot,
                  bottom: 0
              ),
            ],
          ),
        )
    ),
  );

  List<_NavigationIconButton> _createNavigationIconButtonList(Map<int, BottomNavigationDotBarItem> mapItem){
    List<_NavigationIconButton> children = List<_NavigationIconButton>();
    mapItem.forEach((index, item) => children.add(
        _NavigationIconButton
          (item.icon, (index == _indexPageSelected) ? _activeColor : _color,item.onTap,()
        { _changeOptionBottomBar(index); }))
    );
    return children;
  }

  void _changeOptionBottomBar(int indexPageSelected){
    if(indexPageSelected != _indexPageSelected){
      setState(() { _positionLeftIndicatorDot = (_numPositionBase * (indexPageSelected+1))-_numDifferenceBase; });
      _indexPageSelected = indexPageSelected;
    }
  }

}

class BottomNavigationBarItem{
  final IconData icon;
  final NavigationIconButtonTapCallback onTap;
  const BottomNavigationDotBarItem({@required this.icon, this.onTap,}) : assert(icon != null);
}

typedef NavigationIconButtonTapCallback = void Function();

class _NavigationIconButton extends StatefulWidget {

  final IconData _icon;
  final Color _colorIcon;
  final NavigationIconButtonTapCallback _onTapInternalButton;
  final NavigationIconButtonTapCallback _onTapExternalButton;

  _NavigationIconButton(this._icon, this._colorIcon, this._onTapInternalButton, this._onTapExternalButton, {Key key}): super(key: key);

  @override
  _NavigationIconButtonState createState() => _NavigationIconButtonState();

}

class _NavigationIconButtonState extends State<_NavigationIconButton> with SingleTickerProviderStateMixin {

  ValueChanged<int> onItemSelected;
  AnimationController _controller;
  Animation _scaleAnimation;
  double _opacityIcon = 1;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(vsync: this, duration: Duration(milliseconds: 200));
    _scaleAnimation = Tween<double>(begin: 1, end: 0.93).animate(_controller);
  }

  @override
  Widget build(BuildContext context) => GestureDetector(

      onTapDown: (_) {
        _controller.forward();
        setState(() { _opacityIcon = 0.7; });
      },
      onTapUp: (_) {
        _controller.reverse();
        setState(() { _opacityIcon = 1; });
      },
      onTapCancel: () {
        _controller.reverse();
        setState(() { _opacityIcon = 1; });
      },
      onTap: () {

        widget._onTapInternalButton();
        widget._onTapExternalButton();
      },
      child: ScaleTransition(
          scale: _scaleAnimation,
          child: AnimatedOpacity(
              opacity: _opacityIcon,
              duration: Duration(milliseconds: 200),
              child: Icon(widget._icon, color: widget._colorIcon)
          )
      )
  );

}

  

这是我第一次动摇

“如何解决？”