Flutter BottomNavigationBar 组件

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

BottomNavigationBar 常见的属性

属性名	说明
items	List<BottomNavigationBarItem> 底 部 导 航 条按钮集合
iconSize	icon
currentIndex	默认选中第几个
onTap	选中变化回调函数
fixedColor	选中的颜色
type	BottomNavigationBarType.fixed BottomNavigationBarType.shifting

示例代码：

import 'package:flutter/material.dart';
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: Text("tabBar"),
        bottomNavigationBar: BottomNavigationBar(
          items: [
            BottomNavigationBarItem(
              icon: Icon(Icons.home),
              title: Text("首页")
            ),
             BottomNavigationBarItem(
              icon: Icon(Icons.category),
              title: Text("分类")
            ),
            
             BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              title: Text("设置")
            )
          ],
        ),
      )
    );
  }
}

import 'package:flutter/material.dart';
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:Tabs()
    );
  }
}


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

  _TabsState createState() => _TabsState();//_xxx私有变量
}

class _TabsState extends State<Tabs> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: Text("tabBar"),
        bottomNavigationBar: BottomNavigationBar(

          currentIndex: 1,
          onTap: (int index){
              print(index);
          },
          items: [
            BottomNavigationBarItem(
              icon: Icon(Icons.home),
              title: Text("首页")
            ),
             BottomNavigationBarItem(
              icon: Icon(Icons.category),
              title: Text("分类")
            ),
            
             BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              title: Text("设置")
            )
          ],
        ),
      );
  }
}

import 'package:flutter/material.dart';
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:Tabs()
    );
  }
}


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

  _TabsState createState() => _TabsState();
}

class _TabsState extends State<Tabs> {

  int _currentIndex=0;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: Text("tabBar"),
        bottomNavigationBar: BottomNavigationBar(

          currentIndex: this._currentIndex,
          onTap: (int index){
              setState(() {
                  this._currentIndex=index;
              });
          },
          items: [
            BottomNavigationBarItem(
              icon: Icon(Icons.home),
              title: Text("首页")
            ),
             BottomNavigationBarItem(
              icon: Icon(Icons.category),
              title: Text("分类")
            ),
            
             BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              title: Text("设置")
            )
          ],
        ),
      );
  }
}

开发中推荐（抽取分离）：

import 'package:flutter/material.dart';

import 'pages/Tabs.dart';

void main() => runApp(MyApp());
class MyApp extends StatelessWidget {  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:Tabs()
    );
  }
}

tabs.dart

import 'package:flutter/material.dart';
import 'tabs/Home.dart';
import 'tabs/Category.dart';
import 'tabs/Setting.dart';

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

  _TabsState createState() => _TabsState();
}

class _TabsState extends State<Tabs> {

  int _currentIndex=0;
  List _pageList=[
    HomePage(),
    CategoryPage(),
    SettingPage(),
  ];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Flutter Demo"),
        ),
        body: this._pageList[this._currentIndex],
        bottomNavigationBar: BottomNavigationBar(
          currentIndex: this._currentIndex,   //配置对应的索引值选中
          onTap: (int index){
              setState(() {  //改变状态
                  this._currentIndex=index;
              });
          },
          iconSize:36.0,      //icon的大小
          fixedColor:Colors.red,  //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: Text("首页")
            ),
             BottomNavigationBarItem(
              icon: Icon(Icons.category),
              title: Text("分类")
            ),
            
             BottomNavigationBarItem(
              icon: Icon(Icons.settings),
              title: Text("设置")
            )
          ],
        ),
      );
  }
}

home.dart

import 'package:flutter/material.dart';

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

  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Text("首页");
  }
}

 其他类似

即可实现常用的底部导航条tab切换，实现显示不同的页面内容！