1、安装中文官网安装Flutter，然后一直卡在pub upgrade，后来配置了URL：
2、但执行flutter doctor还是报错：[!] Android toolchain - develop for Android devices
3、然后配置AS的环境变量，仍然报错；而且发觉SDK目录下并没tools文件夹；因此怀疑是不是因为工具更新，舍弃了该文件夹；
4、按照此方向，谷歌后得到了解决方案：
You need to open AndroidStudio then go to Tools -> SDK Manager then go to SDK Tools tab, uncheck the option Hide Obsolete Packages
You will see the option of Android SDK Tools (Obsolete), check the option and continue the process download and installation.
https://stackoverflow.com/questions/52256569/android-sdkmanager-tool-not-found
5、大功告成！！
