安装flutter
1．安装android studio ，打开配置plugin 下载安装flutter
2．android sdk，打卡sdk文件夹下tools/android，下载所需sdk版本，
配置环境变量
exportANDROID_HOME=/Users/cody/App/android-sdk-macosx
export PATH=${PATH}:${ANDROID_HOME}/platform-tools
export PATH=${PATH}:${ANDROID_HOME}/tools
export PATH=${PATH}:${ANDROID_HOME}/build-tools/28.0.3
【1】、Android toolchain - develop for Android devices (Android SDK version28.0.3)
! Some Android licenses not accepted. To resolve this, run: flutterdoctor
–android-licenses
本机已安装了AndroidSDK，Android许可不被接受,需要执行以下命令，同意许可
flutter doctor --android-licenses
如果报错Error: Unknown argument --licenses，
执行（确认java版本为java8/jdk1.8）
/Users/yangshanshan/Documents/download-program/android-sdk-macosx/tools/bin/sdkmanager --update
【2】、Xcode - develop for iOS and macOS
✗Xcode installation is incomplete;a full installation is necessary for iOS development.
Download at: https://developer.apple.com/xcode/download/
Or install Xcode via the App Store.
Once installed, run:
sudo xcode-select --switch/Applications/Xcode.app/Contents/Developer
本机已安装了xcode，那就是需要执行以下命令
cmd
sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
sudo xcodebuild -license
【3】、Android Studio (version 3.4)
✗Flutter plugin not installed; thisadds Flutter specific functionality.
✗Dart plugin not installed; thisadds Dart specific functionality.
本机已安装Android Studio，但是缺这两个插件，需要我们去安装一下。
打开Android Studio->configure->Plugins
搜索flutter 进行install
