flutter混合开发报错：Failed to apply plugin [class 'FlutterPlugin']

也忘了之前改过什么了，前几天有个朋友给我留言说flutterMix的工程github的链接打不开。我才想起来前些时间为了应付公司信息安全部门的要求，把我很多项目都给删掉了，如果想恢复只能重新创建上传。

本地flutter项目重新搭起来，报这个错误。百度谷歌了下，没有找到答案，好吧，只能靠自己了。

报错如下：

Project evaluation failed including an error in afterEvaluate {}. Run with --stacktrace for details of the afterEvaluate {} error.

FAILURE: Build failed with an exception.

* Where:
Script '/Users/xxxxx/develop/develop_tool/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 151

* What went wrong:
A problem occurred evaluating script.
> Failed to apply plugin [class 'FlutterPlugin']
   > flutter.sdk must point to the Flutter SDK directory

* 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

CONFIGURE FAILED in 0s
Cause: flutter.sdk must point to the Flutter SDK directory

报错发生在flutter的sdk目录下面，OK，那我们就打开flutter_tools这个工程看一下原因：

flutter_tools/gradle/flutter.gradle下面，

apply plugin: FlutterPlugin

class FlutterPlugin implements Plugin {

可以确定，基本上应该是这个类FlutterPlugin内部报错。

继续向下搜索错误原因：flutter.sdk must point to the Flutter SDK directory，我们找到了这一行：

  String flutterRootPath = resolveProperty("flutter.sdk", System.env.FLUTTER_ROOT)
        if (flutterRootPath == null) {
            throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file or with a FLUTTER_ROOT environment variable.")
        }
        flutterRoot = project.file(flutterRootPath)
        if (!flutterRoot.isDirectory()) {
            throw new GradleException("flutter.sdk must point to the Flutter SDK directory")
        }

看起来，应该是flutterRoot指向错误的原因。

resolveProperty方法点进去看一下，大体上就是优先读取工程下面local.properties文件中的flutter.sdk值，如果没有，那么就去系统环境变量中找。

一开始我以为是没有设置环境变量中的flutter.sdk导致的，但是后来设置上了，还是不行报同样的错误。

所以后来灵机一动，直接编辑了上面的flutter.gradle文件，添加下面的这行代码：

 String flutterRootPath = resolveProperty(project, "flutter.sdk", System.env.FLUTTER_ROOT)
        if (flutterRootPath == null) {
            throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file or with a FLUTTER_ROOT environment variable.")
        }
        flutterRoot = project.file(flutterRootPath)
//添加这行代码，直接打印出来所有数据
        throw new GradleException("FLUTTER_ROOT:"+System.env.FLUTTER_ROOT+",flutterRootPath:"+flutterRootPath+",project.projectDir.parentFile:"+project.projectDir.parentFile.getAbsolutePath())
        if (!flutterRoot.isDirectory()) {
            throw new GradleException("flutter.sdk must point to the Flutter SDK directory")
        }

最后报错：

A problem occurred evaluating script.
> Failed to apply plugin [class 'FlutterPlugin']
   > FLUTTER_ROOT:/Users/xxxx/develop/develop_tool/flutter,flutterRootPath:/Users/xxxx/develop/flutter,project.projectDir.parentFile:/Users/xxxx/develop/git_ware/flutter_mix/flutterMix/my_flutter/.android

OK，这样我们就知道了，原来读取的是

Users/xxxx/develop/git_ware/flutter_mix/flutterMix/my_flutter/.android

下面的local.properties文件中的flutter.sdk变量导致的，我们改下这个变量，指向正确的目录地址就解决问题了。

那么为什么会出现这个问题的原因也浮出了水面，肯定是我不注意间挪了flutter.sdk的目录地址导致的。