demo注释-使用 Themes 统一颜色和字体风格

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final appName = 'Custom Themes';

    return MaterialApp(
      title: appName,
      theme: ThemeData(//定义一个全局 theme
        // Define the default brightness and colors.
        brightness: Brightness.dark,
        primaryColor: Colors.lightGreen[800],
        accentColor: Colors.deepOrangeAccent,

        // Define the default font family.
        fontFamily: 'Montserrat',

        // Define the default TextTheme. Use this to specify the default
        // text styling for headlines, titles, bodies of text, and more.
        textTheme: TextTheme(
          headline: TextStyle(fontSize: 72.0, fontWeight: FontWeight.bold),
          title: TextStyle(fontSize: 36.0, fontStyle: FontStyle.italic),
          body1: TextStyle(fontSize: 14.0, fontFamily: 'Hind'),
        ),
      ),
      home: MyHomePage(
        title: appName,
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

  MyHomePage({Key key, @required this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Container(
          color: Theme.of(context).accentColor,//沿用父及Theme的accentColor样式
          child: Text(
            'Text with a background color',
            style: Theme.of(context).textTheme.title,//这里的title 是指textTheme中文本的一种呈现方式，还有很多种，具体可点进去查看。
          ),
        ),
      ),
      floatingActionButton: Theme(
        data: Theme.of(context).copyWith(
          colorScheme:
          Theme.of(context).colorScheme.copyWith(secondary: Colors.yellow),//从父级 Theme 扩展其他属性，使用 copyWith 方法即可。
        ),
        child: FloatingActionButton(
          onPressed: null,
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}