BottomNavigationBar 是底部导航栏控件. 可以让我们定义底部 Tab 切换，bottomNavigationBar 是 Scaffold 组件的参数。

BottomNavigationBar 的基本属性

栗子

import 'package:flutter/material.dart';
import './pages/home.dart';
import './pages/Category.dart';
import './pages/Setting.dart';

class MainPageWidget extends StatefulWidget {
  MainPageWidget({Key key}) : super(key: key);

  _MainPageWidgetState createState() => _MainPageWidgetState();
}

class _MainPageWidgetState extends State<MainPageWidget> {
  int _tabIndex = 0; // tab 的标记
  var appBarTitles = ['首页', '发现', '我的'];
  List _pageList = [
    Homepage(),
    CategoryPage(),
    SettingPage(),
  ];
  /*
   * 获取bottomTab的颜色和文字
   */
  Text getTabTitle(int curIndex) {
    if (curIndex == _tabIndex) {
      return new Text(appBarTitles[curIndex],
          style: new TextStyle(fontSize: 14.0, color: const Color(0xff1296db)));
    } else {
      return new Text(appBarTitles[curIndex],
          style: new TextStyle(fontSize: 14.0, color: const Color(0xff515151)));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: this._pageList[this._tabIndex],  //内容的切换
        bottomNavigationBar: BottomNavigationBar(
          currentIndex: this._tabIndex, //配置对应的索引值选中
          onTap: (int index) {
            setState(() {
              //改变状态
              this._tabIndex = index;
            });
          },
          iconSize: 36.0, //icon的大小
          fixedColor: Color(0xff1296db), //选中的颜色
          type: BottomNavigationBarType.fixed, //配置底部tabs可以有多个按钮
          items: [
            BottomNavigationBarItem(
                icon: Icon(Icons.home), title: getTabTitle(0)),
            BottomNavigationBarItem(
                icon: Icon(Icons.category), title: getTabTitle(1)),
            BottomNavigationBarItem(
                icon: Icon(Icons.settings), title: getTabTitle(2))
          ],
        ),
      ),
    );
  }
}

BottomNavigationBar 的简单封装

import 'package:flutter/material.dart';

/*
 *导航栏的封装 
 */
class MainTabWidget extends StatefulWidget {
  List<Widget> pageList; //页面

  List<String> titleList = List(); // 标题，可以为空。默认为控字符串

  List<Icon> iconList = List(); // 标题，可以为空。默认为控字符串

  Color navBackgroundColor;

  MainTabWidget(this.pageList,
      {List<String> titles, List<Icon> icons, this.navBackgroundColor}) {
    if (titles == null || titles.length < 1) {
      for (int i = 0; i < pageList.length; i++) {
        // 由于BottomNavigationBarItem必须要设置一个标题。默认给一个空字符串
        titleList.add("");
      }
    }else{
      this.titleList =titles;
    }
    if (icons == null || icons.length < 1) {
      for (int i = 0; i < pageList.length; i++) {
        // 添加默认图标-add default icon
        iconList.add(Icon(Icons.home));
      }
    }else{
      this.iconList =icons;
    }
    if (pageList == null || pageList.length < 1) {
      // 内容界面为空，抛出 异常
      throw FormatException('one page at least!');
    }

    if (pageList == null ||
        pageList.length < 1 ||
        pageList.length != titleList.length ||
        pageList.length != iconList.length) {
      // 内容界面数量、标题数量、图标数量不一致，抛出异常。
      throw FormatException('data list is null or not equal!');
    }
  }

  _MainTabWidgetState createState() => _MainTabWidgetState();
}

class _MainTabWidgetState extends State<MainTabWidget> {
  // 保存当前选中的位置
  int _currentIndex = 0;
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Scaffold(
        body: widget.pageList[_currentIndex],
        bottomNavigationBar: BottomNavigationBar(
          items: this._getNavItems(),
          iconSize: 20.0,
      
          // 设置当前选中位置
          currentIndex: this._currentIndex,
          // 点击事件->设置当前选中位置,重新刷新界面
          onTap: (index) {
            setState(() {
              this._currentIndex = index;
            });
          },
          // 设置BottomNavigationBar背景颜色，默认设置为白色
          backgroundColor: widget.navBackgroundColor == null
              ? Colors.white
              : widget.navBackgroundColor,
        ),
      ),
    );
  }

  List<BottomNavigationBarItem> _getNavItems() {
    List<BottomNavigationBarItem> items = List();
    for (int i = 0; i < widget.titleList.length; i++) {
      items.add(BottomNavigationBarItem(
        icon: widget.iconList[i],
        title: Text(widget.titleList[i]),
      ));
    }
    return items;
  }
}

简单的使用:

import './view/MainTabWidget.dart';
import './view/pages/home.dart';
import './view/pages/Category.dart';
import './view/pages/Setting.dart';

//程序的入口方法  D:\Program Files\Nox\bin
void main() {
  // runApp 是 Fltutter 给我提供app 启动的方法,里面可以传入组件
  runApp(MyApp());
}

//StatelessWidget 是一个静态组件
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    List<String> appBarTitles = ['首页', '发现', '我的'];
    List<Icon> iconList = [
      Icon(Icons.home),
      Icon(Icons.album),
      Icon(Icons.settings)
    ];

    List<Widget> pageList = [
      Homepage(),
      CategoryPage(),
      SettingPage(),
    ];
    return MaterialApp(
        home: MainTabWidget(pageList,
            navBackgroundColor: Colors.cyan,
            titles: appBarTitles,
            icons: iconList));
  }
}