BottomNavigationBar 自定义 底部导航条

在flutter中，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 

• items ：List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

基本实现

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")
            )
          ],
        ),
      )
    );
  }
}

切换选中

当我们点击按钮，想要切换选中的导航块时，需要监听onTap，然后改变currentIndex。

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")
            )
          ],
        ),
      );
  }
}

  

需要特别说明的是，默认可以显示两个或者三个BottomNavigationBarItem，如果有更多的BottomNavigationBarItem需要显示，则需要配置type的为BottomNavigationBarType.fixed，否则样式会出现问题。

页面切换

 要实现点击后页面切换的效果，首先需要有三个页面，在flutter中，一切皆组件，页面也是组件。

首先，在lib目录下新建pages文件夹，然后在pages下新建文件夹tabs，并新建上面导航对应的三个页面。

Category.dart

import 'package:flutter/material.dart';

class CategoryPage extends StatefulWidget {
  CategoryPage({Key key}) : super(key: key);
  _CategoryPageState createState() => _CategoryPageState();
}

class _CategoryPageState extends State<CategoryPage> {
  @override
  Widget build(BuildContext context) {
    return Text("分类");
  }
}

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("我是首页组件");
  }
}

Setting.dart

import 'package:flutter/material.dart';

class SettingPage extends StatefulWidget {
  SettingPage({Key key}) : super(key: key);
  _SettingPageState createState() => _SettingPageState();
}

class _SettingPageState extends State<SettingPage> {
  @override
  Widget build(BuildContext context) {
    return ListView(
      children: <Widget>[
        ListTile(
          title: Text("我是一个文本"),
        ),
         ListTile(
          title: Text("我是一个文本"),
        ),
         ListTile(
          title: Text("我是一个文本"),
        ),
         ListTile(
          title: Text("我是一个文本"),
        )
      ],
    );
  }
}

然后，在pages文件夹下新建Tabs.dart文件，并将上面例子中的tabs组件剪切到这个文件中，

import 'package:flutter/material.dart';
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")
            )
          ],
        ),
      );
  }
}

最后，在main.dart中引入Tabs.dart

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()
    );
  }
}

此时，仅仅只是实现上面例子中的效果，还不能实现页面的切换，还需要继续修改Tabs.dart文件。

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")
            )
          ],
        ),
      );
  }
}

 代码下载：点这里  提取码(xsju)