Flutter项目转V2 embedding后编译失败FlatButton未定义报错

运行GitHub上的flutter_alarm_clock时钟项目（项目地址：https://github.com/afzalali15/flutter_alarm_clock）时，最初构建提示需要Convert to V2 embedding，按官方迁移步骤完成配置更新后，再次构建出现报错无法编译，报错日志如下：

Launching lib\main.dart on sdk gphone64 x86 64 in debug mode...
Running Gradle task 'assembleDebug'...
Warning: Mapping new ns http://schemas.android.com/repository/android/common/02 to old ns http://schemas.android.com/repository/android/common/01
Warning: Mapping new ns http://schemas.android.com/repository/android/generic/02 to old ns http://schemas.android.com/repository/android/generic/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/addon2/02 to old ns http://schemas.android.com/sdk/android/repo/addon2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/addon2/03 to old ns http://schemas.android.com/sdk/android/repo/addon2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/repository2/02 to old ns http://schemas.android.com/sdk/android/repo/repository2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/repository2/03 to old ns http://schemas.android.com/sdk/android/repo/repository2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/sys-img2/03 to old ns http://schemas.android.com/sdk/android/repo/sys-img2/01
Warning: Mapping new ns http://schemas.android.com/sdk/android/repo/sys-img2/02 to old ns http://schemas.android.com/sdk/android/repo/sys-img2/01
Warning: unexpected element (uri:"", local:"extension-level"). Expected elements are <{}codename>,<{}layoutlib>,<{}api-level>
Warning: unexpected element (uri:"", local:"base-extension"). Expected elements are <{}codename>,<{}layoutlib>,<{}api-level>
lib/views/homepage.dart:65:16: Error: The method 'FlatButton' isn't defined for the class '_HomePageState'.
 - '_HomePageState' is from 'package:clock_app/views/homepage.dart' ('lib/views/homepage.dart').
Try correcting the name to the name of an existing method, or defining a method named 'FlatButton'.
        return FlatButton(
               ^^^^^^^^^^
lib/views/alarm_page.dart:157:36: Error: The method 'FlatButton' isn't defined for the class '_AlarmPageState'.
 - '_AlarmPageState' is from 'package:clock_app/views/alarm_page.dart' ('lib/views/alarm_page.dart').
Try correcting the name to the name of an existing method, or defining a method named 'FlatButton'.
                            child: FlatButton(
                                   ^^^^^^^^^^
lib/views/alarm_page.dart:179:47: Error: The method 'FlatButton' isn't defined for the class '_AlarmPageState'.
 - '_AlarmPageState' is from 'package:clock_app/views/alarm_page.dart' ('lib/views/alarm_page.dart').
Try correcting the name to the name of an existing method, or defining a method named 'FlatButton'.
                                              FlatButton(
                                              ^^^^^^^^^^


FAILURE: Build failed with an exception.

* Where:
Script 'C:\src\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 1159

* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\src\flutter\bin\flutter.bat'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 36s
Exception: Gradle task assembleDebug failed with exit code 1

• 日志开头的namespace映射、unexpected element警告是旧版Gradle插件和本地新版Android SDK不兼容导致的，不会直接造成构建失败，可以暂时忽略。
• 构建失败的核心原因是代码中使用的FlatButton组件不存在：该项目基于早期Flutter版本开发，FlatButton是旧版本Material组件，Flutter 2.0及之后的版本已经正式废弃并移除了这个组件，替换为TextButton，本地高版本Flutter无法识别旧组件名就会抛出编译错误。

1. 替换废弃组件
   找到项目中3处使用FlatButton的位置，直接将组件名替换为TextButton即可，两者参数完全兼容，不需要修改其他属性配置。对应文件位置：

• lib/views/homepage.dart 第65行
• lib/views/alarm_page.dart 第157行
• lib/views/alarm_page.dart 第179行

2. 清理构建缓存
   在项目根目录执行以下命令，清除旧的构建缓存并重新拉取依赖：

flutter clean
flutter pub get

3. 重新启动项目即可正常编译运行。

如果需要消除开头的Android相关警告，可以把android目录下build.gradle中的Gradle插件版本升级到和本地Flutter版本匹配的版本，不升级也不会影响项目功能正常运行。

内容的提问来源于stack exchange，提问作者Vinay Hegde