Now, let’s use the theme we initially created in our main function for a simple login screen:

现在，让我们使用最初在主函数中创建的主题来制作一个简单的登录屏幕：

Create a Login Screen Widget: Inside the main.dartfile, create a new widget named LoginScreen thatextends StatelessWidget.

创建登录屏幕小部件： 在main.dart文件中，创建一个名为LoginScreen的新部件，它是StatelessWidget的扩展。

Import Required Libraries: Import the necessaryFlutter libraries at the top of your Dart file:

导入所需库： 在 Dart 文件顶部导入必要的 Flutter 库：

import ‘package:flutter/material.dart’;

Define the LoginScreen Widget: Design your login screen using the defined theme. You can use various widgets like TextField, ElevatedButton, and Text to build your UI. Apply the theme’s attributes to achieve a consistent style. The final source should look like this:

定义登录屏幕小工具： 使用定义的主题设计登录界面。您可以使用 TextField、ElevatedButton 和 Text 等各种部件来构建用户界面。应用主题属性以实现一致的风格。最终的源文件应该是这样的

import "package:flutter/material.dart";

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "用户登录",
      theme: ThemeData(
        brightness: Brightness.dark,
        primaryColor: Colors.lightBlue[800],
        fontFamily: "Georgia",
        textTheme: const TextTheme(
          displayLarge: TextStyle(fontSize: 70, fontWeight: FontWeight.bold),
          titleLarge: TextStyle(fontSize: 34, fontStyle: FontStyle.italic),
          bodyMedium: TextStyle(fontSize: 12, fontFamily: "Roboto"),
        ),
      ),
      home: const LoginScreen(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("用户登录"),
      ),
      body: Center(
          child: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              "欢迎登录",
              style: Theme.of(context).textTheme.titleLarge,
            ),
            const TextField(
              decoration: InputDecoration(
                  labelText: "账号", prefixIcon: Icon(Icons.person)),
            ),
            const SizedBox(height: 20),
            const TextField(
              decoration: InputDecoration(
                  labelText: "密码", prefixIcon: Icon(Icons.lock)),
              obscureText: true,
            ),
            const SizedBox(height: 20),
            ElevatedButton(
              onPressed: () {
                // Add your login logic here
              },
              child: const Text("登录"),
            ),
          ],
        ),
      )),
    );
  }
}

效果预览:

Apply the Theme: Notice how we’ve used Theme.of(context).textTheme.titleLarge to set the style of our ‘Welcome’ Text widget. You can also do the same to other widgets as you desire.

应用主题： 注意我们是如何使用 Theme.of(context).textTheme.titleLarge 来设置 “欢迎 ”文本部件的样式的。您也可以根据需要对其他部件进行同样的设置。

Launch the App with LoginScreen: Inside the main function, launch the app with the MaterialApp widget and the LoginScreen as the home screen: You should see the following output.

使用 LoginScreen 启动应用程序： 在主函数中，使用 MaterialApp 部件和 LoginScreen 作为主屏幕启动应用程序： 您应该会看到以下输出。

Make changes: The current theme of the login screen is dark. To make it light, you can change the ‘brightness’ property of ThemeData in the main function to light.

进行更改： 当前登录界面的主题是暗色。要使其变亮，可将主函数中主题数据的 “亮度 ”属性更改为亮色。

brightness: Brightness.light

Run the app: When you run the app again, you should see this new look.

运行应用程序： 再次运行应用程序时，你应该会看到这个新外观。

As you follow these steps, you’re creating a login screen with a consistent color scheme based on the defined theme. This ensures that your app’s UI maintains a unified and professional appearance.

按照这些步骤操作后，您就可以根据定义的主题创建具有统一配色方案的登录屏幕。这样可以确保应用程序的用户界面保持统一和专业的外观。

At the end of this section, your main.dart file should contain the complete code for the login app with a theme. Remember that using themes in Flutter not only helps maintain a consistent look but also simplifies the process of styling your app’s UI elements.

本节结束时，您的 main.dart 文件应包含登录应用程序的完整代码和主题。请记住，在 Flutter 中使用主题不仅有助于保持外观一致，还能简化应用程序 UI 元素的样式设计过程。