解决Flutter不能下载jar包问题

因为不可访问Google，所以直接下载Jar存在问题。

解决办法：

• 更改Gradle仓库地址，使用阿里云加速：修改Flutter SDK安装目录下的\packages\flutter_tools\gradle\flutter.gradle文件

  buildscript {
      repositories {
          //google()
         // jcenter()
          maven{ url 'https://maven.aliyun.com/repository/google' }
          maven{ url 'https://maven.aliyun.com/repository/jcenter' }
          maven{url 'http://maven.aliyun.com/nexus/content/groups/public'}
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:3.2.1'
      }
  }
  

• 配置项目内的build.gradle文件
  

  buildscript {
      repositories {
  //        google()
  //        jcenter()
          maven{ url 'https://maven.aliyun.com/repository/google' }
          maven{ url 'https://maven.aliyun.com/repository/jcenter' }
          maven{url 'http://maven.aliyun.com/nexus/content/groups/public'}
  
      }
  
      dependencies {
          classpath 'com.android.tools.build:gradle:3.2.1'
      }
  }
  
  allprojects {
      repositories {
  //        google()
  //        jcenter()
          maven{ url 'https://maven.aliyun.com/repository/google' }
          maven{ url 'https://maven.aliyun.com/repository/jcenter' }
          maven{url 'http://maven.aliyun.com/nexus/content/groups/public'}
  
      }
  }