Theme

主题即在我们的应用程序中共享颜色和字体样式，比如导航栏颜色、标题字体、Icon样式等

实现

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ThemeTestRoute(),
    );
  }
}
class ThemeTestRoute extends StatefulWidget {
  @override
  _ThemeTestRouteState createState() => new _ThemeTestRouteState();
}

class _ThemeTestRouteState extends State<ThemeTestRoute> {
  Color _themeColor = Colors.teal; //当前路由主题色

  @override
  Widget build(BuildContext context) {
    ThemeData themeData = Theme.of(context);
    return Theme(
      data: ThemeData(
          primarySwatch: _themeColor, //用于导航栏、FloatingActionButton的背景色等
          iconTheme: IconThemeData(color: _themeColor) //用于Icon颜色
      ),
      child: Scaffold(
        appBar: AppBar(title: Text("主题测试")),
        body: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            //第一行Icon使用主题中的iconTheme
            Row(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Icon(Icons.favorite),
                  Icon(Icons.airport_shuttle),
                  Text("  颜色跟随主题")
                ]
            ),
            //为第二行Icon自定义颜色（固定为黑色)
            Theme(
              data: themeData.copyWith(
                iconTheme: themeData.iconTheme.copyWith(
                    color: Colors.black
                ),
              ),
              child: Row(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    Icon(Icons.favorite),
                    Icon(Icons.airport_shuttle),
                    Text("  颜色固定黑色")
                  ]
              ),
            ),
          ],
        ),
        floatingActionButton: FloatingActionButton(
            onPressed: () =>  //切换主题
                setState(() =>
                _themeColor =
                _themeColor == Colors.teal ? Colors.blue : Colors.teal
                ),
            child: Icon(Icons.palette)
        ),
      ),
    );
  }
}

切换效果：

summary

学习效率愈加下降，看来还是需要从官方文档啃着走，推荐一个官方中文Flutter网站：
https://flutter-io.cn/ 上面有许多中文学习资源：

当然中文文档（https://flutter-io.cn/docs）目前的开发几乎没有开始，只是翻译了个目录，所以中文文档还是可以看Flutter中文网：https://flutterchina.club/docs/