Mac 环境 Gradle project Sync Failed 解决方法

一、Gradle 下载失败导致出错，timeout

找到grapple-wrapper.properties 在最下面的 distributionUrl 查看自己的 gradle 版本（我是 gradle-4.6-all.zip），复制链接的 URL，自行下载压缩包。
打开终端输入 open ~/. gradle ，会自动进入 Finder，gradle 所在的目录。
将自行下载的压缩包复制到对应版本的文件夹下（以我的版本为例：我们下在的压缩包应该存放的目录为：~/.gradle/gradle-4.6/xxxxxxxxx/gradle-4.6-all，xxxxx 表示一堆乱七八糟的字符，最好先把原文件夹内的文件先删除），并解压缩。
再次执行编译，应该可以正常通过。

二、Error running Gradle，jar 文件下载失败

问题详情：

Launching lib/main.dart on Android SDK built for x86 in debug mode...
Initializing gradle...
Resolving dependencies...
* Error running Gradle:
ProcessException: Process "/Users/rabbit/develop/android/flutter_app/android/gradlew" exited abnormally:
Project evaluation failed including an error in afterEvaluate {}. Run with --stacktrace for details of the afterEvaluate {} error.

FAILURE: Build failed with an exception.

* Where:
Build file '/Users/rabbit/develop/android/flutter_app/android/app/build.gradle' line: 25

* What went wrong:
A problem occurred evaluating project ':app'.
> Could not resolve all files for configuration 'classpath'.
   > Could not find lint-gradle-api.jar (com.android.tools.lint:lint-gradle-api:26.1.2).
     Searched in the following locations:
         https://jcenter.bintray.com/com/android/tools/lint/lint-gradle-api/26.1.2/lint-gradle-api-26.1.2.jar

* 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 0s
  Command: /Users/rabbit/develop/android/flutter_app/android/gradlew app:properties

Finished with error: Please review your Gradle project setup in the android/ folder.

提示 .jar 文件下载失败。

解决方法：

步骤1：修改build.gradle,注释掉jcenter()，google()。使用阿里的镜像。原因是 jcenter google 库无法访问到导致的问题。虽然我有万能的爬墙工具，开启全局代理依然被我们伟大的发改委墙掉了！

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:3.1.2'
    }
}

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' }
    }
}


第二步：找到 fluttersdk 目录 进入如下目录

Macintosh HD⁩ ▸ ⁨用户⁩ ▸ ⁨rabbit⁩ ▸ ⁨资源库⁩ ▸ ⁨Flutter⁩ ▸ ⁨packages⁩ ▸ ⁨flutter_tools⁩ ▸ ⁨gradle⁩
找到下 flutter.gradle 文件 找如如下内容替换成和我一样的把 jcenter()，google() 注释掉。

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:3.1.2'
    }
}

// 重新运行，解决掉问题。