【Flutter】【widget】AppBar 顶部状态栏

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前言

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一、AppBar 是什么？

顶部状态栏的快速实现。默认新建的时候有一个标题。

二、使用步骤

1.布局如图

2.参数说明

• centerTitle: true, 标题是否居中，ios 和android 风格不一样
• shadowColor: Colors.green, 阴影的颜色
• // surfaceTintColor: Colors.red,
• backgroundColor: Colors.red, //背景颜色
• foregroundColor: Colors.indigo, //应用程序栏中[Text]和[Icon]的默认颜色,如果没有设置就会使用该颜色
• elevation: 10, //阴影
• iconTheme: const IconThemeData(
  size: 40, color: Colors.black), //app bar 所有的里面的图标主题设置
• shape: const RoundedRectangleBorder(
  borderRadius: BorderRadius.all(Radius.circular(15))), //设置形状
• leading: const Icon(Icons.arrow_circle_down_rounded),
• automaticallyImplyLeading: false,
• actions: [
  IconButton(onPressed: () {}, icon: const Icon(Icons.downhill_skiing)),
  IconButton(onPressed: () {}, icon: const Icon(Icons.padding)),
  ],
• // flexibleSpace: Container(
  // height: 20,
  // color: Colors.red,
  // ),
• title: const Text(“我是标题”), //标题*

代码如下（示例）：

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
              centerTitle: true,
        shadowColor: Colors.green,
        // surfaceTintColor: Colors.red,
        backgroundColor: Colors.red, //背景颜色
        foregroundColor: Colors.indigo, //应用程序栏中[Text]和[Icon]的默认颜色,如果没有设置就会使用该颜色
        elevation: 10,
        iconTheme: const IconThemeData(
            size: 40, color: Colors.black), //app bar 所有的里面的图标主题设置
        shape: const RoundedRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(15))), //设置形状
        leading: const Icon(Icons.arrow_circle_down_rounded),
        automaticallyImplyLeading: false,
        actions: [
          IconButton(onPressed: () {}, icon: const Icon(Icons.downhill_skiing)),
          IconButton(onPressed: () {}, icon: const Icon(Icons.padding)),
        ],
        // flexibleSpace: Container(
        //   height: 20,
        //   color: Colors.red,
        // ),
        title: const Text("我是标题"), //标题
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

2.特别的bottom

1.PreferredSize

在appbar 下面的botton 可以作为顶部导航栏的功能实现，他看也是一个widget:

      appBar: AppBar(
        centerTitle: true,

        title: const Text("我是标题"), //标题
        bottom: const PreferredSize(
            child: Text('PreferredSize'), preferredSize: Size(10, 10)),
      ),

2.作为顶部导航栏

TabBar 和 TabBarView 配合使用，lenth两个要一致不然会报错，然后需要TabController

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage>
    with SingleTickerProviderStateMixin {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  final tabNameList = ["热门", "本地", "新闻", "优惠"];
  late TabController _tabController;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _tabController = TabController(length: tabNameList.length, vsync: this);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.pink,
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(15))),
        centerTitle: true,
        title: const Text("我是标题"), //标题
        bottom: TabBar(
            controller: _tabController,
            isScrollable: true, //可滚动
            indicatorColor: Colors.indigo, //指示器的颜色
            labelColor: Colors.white, //选中文字颜色
            unselectedLabelColor: Colors.black, //没有选中文字颜色

            tabs: <Widget>[
              for (int i = 0; i < tabNameList.length; i++)
                Tab(text: tabNameList[i])
            ]),
      ),
      body: TabBarView(
          controller: _tabController,
          children: tabNameList
              .map((e) => Center(
                    child: Text(e),
                  ))
              .toList()),

      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

3.其他 AppBar 可以设置透明？

在scaffold下面：设置颜色等
但是其他事不需要设置透明，直接去掉，然后自己新建widget。完美

extendBody: true, //底部NavigationBar透明
extendBodyBehindAppBar: true,//顶部Bar透明

3.backbutton

如果构建了appbar，并且不是在主页面的情况，会自动生成backbutton 按键，点击默认靠右返回到上一个页面.

第二个页面，点击floatbutton 跳转到第二个页面

class SecondPage extends StatefulWidget {
  const SecondPage({Key? key}) : super(key: key);

  @override
  _SecondPageState createState() => _SecondPageState();
}

class _SecondPageState extends State<SecondPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('second page'),
      ),
      body: Container(
        color: Colors.red,
      ),
    );
  }
}

总结

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