Android Studio导入Flutter项目、解决旧Flutter项目不支持空安全所出现的一些问题

1. 下载Flutter SDK：https://storage.googleapis.com/dart-archive/channels/stable/release/2.19.3/sdk/dartsdk-windows-x64-release.zip
   解压到你想要放的目录。

2. 配置Flutter SDK的环境变量，配置flutter/bin这个目录

3. settings -> marketplace -> plugins -> 搜索Flutter插件 ->安装Flutter插件，会提示安装Dart插件，点击确定都安装。

4. Project Sctucture 设置Java的SDK版本为Java 11

5. win + R打开cmd -> 运行命令：flutter doctor

   提示：

   Doctor summary (to see all details, run flutter doctor -v):
   [√] Flutter (Channel stable, 3.7.6, on Microsoft Windows [版本 10.0.22000.1574], locale zh-CN)
   [X] Windows Version (Unable to confirm if installed Windows version is 10 or greater)
   [!] Android toolchain - develop for Android devices (Android SDK version 32.1.0-rc1)
       X cmdline-tools component is missing
         Run `path/to/sdkmanager --install "cmdline-tools;latest"`
         See https://developer.android.com/studio/command-line for more details.
       X Android license status unknown.
         Run `flutter doctor --android-licenses` to accept the SDK licenses.
         See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.
   [√] Chrome - develop for the web
   [X] Visual Studio - develop for Windows
       X Visual Studio not installed; this is necessary for Windows development.
         Download at https://visualstudio.microsoft.com/downloads/.
         Please install the "Desktop development with C++" workload, including all of its default components
   [√] Android Studio (version 2022.1)
   [√] Connected device (4 available)
   [√] HTTP Host Availability
   
   ! Doctor found issues in 3 categories.
   

6. 运行命令：

   flutter channel
   flutter channel master
   

   解决：Windows Version (Unable to confirm if installed Windows version is 10 or greater)

打开Android Studio -> Android SDK -> SDK Tools -> 找到cmdline-tools，安装即可。
解决：cmdline-tools component is missing

flutter doctor --android-licenses

解决：Android license status unknown.

Visual Studio - develop for Windows就不管了，因为用的时Android Studio开发。

7. Settings -> Flutter -> 配置Flutter SDK的路径
   Settings -> Dart -> 配置Dart SDK路径，一般配置好Flutter SDK，Dart SDK也会有了。

8. 导入项目，提示：

   'Pub get' has not been run，找到pubspec.yaml，点击Pub get
   

   提示：

   The lower bound of "sdk: '>=2.6.0 <3.0.0'" must be 2.12.0 or higher to enable null safety.
   

   修改：

   environment:
     sdk: ">=2.12.0 <3.0.0"
   

9. 继续'Pub get'提示：

   Because fun_lab depends on json_serializable >=0.1.0+1 <4.1.0 which doesn't support null safety, version solving failed.

   修改：

   json_annotation: ^4.0.1
   json_serializable: ^4.1.2
   

上面这些提示其实把版本提上去就好了，提到支持空安全的版本就行。
也可以用命令更新：

dart pub upgrade --null-safety
dart pub get

查看Flutter插件库版本的网站，可以在这里查找插件：
https://pub.dev/

其实高版本的Flutter到这里项目应该就能跑起来了。

一顿操作猛如虎，结果项目太老旧了，用到的很多插件都已经不维护了，没有支持空安全的版本。没办法，只能想其它办法：

百度搜出来的办法：

1. 运行/编译项目时加参数禁用空安全

   flutter run --no-sound-null-safety
   flutter build --no-sound-null-safety
   

3. 修改pubspec.yaml中sdk的版本号

   environment:
     # sdk: ">=2.12.0 <3.0.0"   // 2.12支持空安全
     sdk: ">=2.11.0 <3.0.0" // 2.11.0不支持
   

一波操作之后也是不行。

最后：降级flutter版本，下载Flutter1.22.4，因为这个版本的Dart版本是 2.10.4，小于2.12。

降级之后，配置Android SDK环境变量：

ANDROID_HOME：C:\Users\Admin\AppData\Local\Android\Sdk

Path配置

%ANDROID_HOME%\emulator
%ANDROID_HOME%\platform-tools
%ANDROID_HOME%\tools

再使用flutter doctor检查配置环境，一顿操作，改了一些问题之后项目终跑起来了。

Flutter学习的一些网站：

1. Flutter官方文档：https://flutter.dev/docs
2. Flutter中文网：https://flutterchina.club/
3. Flutter实战：https://book.flutterchina.club/