如何将 Flutter 应用主题默认设置为深色？

我在 flutter 中创建了一个简单的登录 UI，但我不知道如何使应用程序的整体主题变暗。我的意思是，将来，如果我向应用程序添加更多功能，它应该全部采用深色主题。有什么办法可以做到这一点吗？

我使用了一个单独的 dart 文件 (login.dart)，并且我的登录 UI 中使用的所有小部件都在此文件中。我已在主 dart 文件 (main.dart) 中将 ThemeData 设置为深色，但应用程序仍在浅色主题中运行。

这是我的代码：

main.dart

import 'package:flutter/material.dart';
import 'package:bidder_login/login.dart';

void main(){
    runApp(
        MaterialApp(
      theme: ThemeData(),
      darkTheme: ThemeData.dark(),
            debugShowCheckedModeBanner: false,
            title: "Basic Login Demo",
            home: LoginPage(),
        ),
    );
}

登录.dart

import 'package:flutter/material.dart';

class LoginPage extends StatefulWidget {
    @override
    _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
    @override
    Widget build(BuildContext context) {
        return Scaffold(
            body: SafeArea(
                child: ListView(
                    padding: EdgeInsets.symmetric(horizontal: 24.0),
                    children: <Widget>[
                        SizedBox(height: 80.0),
                        // Column(
                        //  children: <Widget>[
                        //      Image.asset('assets/login_app.png'),
                        //      SizedBox(height: 25.0),
                        //      Text("Material Login"),
                        //  ],
                        // ),

                        //*Username starts here
                        SizedBox(height: 120.0),
                        TextField(
                            decoration: InputDecoration(
                                labelText: 'Username',
                                filled: true,
                            ),
                        ),

                        //*Password starts here
                        SizedBox(height: 12.0),
                        TextField(
                            decoration: InputDecoration(
                                labelText: 'Password',
                                filled: true,
                            ),
                            obscureText: true,
                        ),
                        ButtonBar(
                            children: <Widget>[
                                FlatButton(
                                    child: Text('Cancel'),
                                    onPressed: () {

                                    },
                                ),
                                RaisedButton(
                                    child: Text('Next'),
                                    onPressed: () {

                                    },
                                )
                            ],
                        )

                    ],
                ),
            ),
        );
    }
}

你需要使用ThemeMode https://api.flutter.dev/flutter/material/ThemeMode-class.html

• 描述了哪些theme将被使用MaterialApp.

示例代码

themeMode: ThemeMode.dark,//Always use the dark mode (if available) regardless of system preference.


themeMode: ThemeMode.light,//Always use the light mode regardless of system preference.


themeMode: ThemeMode.system,//Use either the light or dark theme based on what the user has selected in the system settings.


themeMode: ThemeMode.values,//A constant List of the values in this enum, in order of their declaration.

如何使用ThemeMode in MaterialApp

MaterialApp(
      debugShowCheckedModeBanner: false,
      theme:
          ThemeData(primarySwatch: Colors.blue, brightness: Brightness.light),
      themeMode: ThemeMode.dark,
      darkTheme: ThemeData(brightness: Brightness.dark),
      home: SafeArea(
          child:Scaffold(

          ) ),
    );