Flutter安装环境

系统要求
要安装并运行Flutter，您的开发环境必须满足以下最低要求:

操作系统: macOS (64-bit)
磁盘空间: 700 MB (不包括Xcode或Android Studio的磁盘空间）.
工具: Flutter 依赖下面这些命令行工具.
bash, mkdir, rm, git, curl, unzip, which

1、设置镜像
由于在国内访问Flutter有时可能会受到限制，Flutter官方为中国开发者搭建了临时镜像，大家可以将如下环境变量加入到用户环境变量中：

export PUB_HOSTED_URL=https://pub.flutter-io.cn
export FLUTTER_STORAGE_BASE_URL=https://storage.flutter-io.cn

2、安装Flutter SDK

// 安装目录，以development为例，没有自己创建一个development文件夹
cd ~/development
// 下载flutter
git clone https://github.com/flutter/flutter.git

下载完成之后，添加flutter相关工具到path中：

export PATH=`pwd`/flutter/bin:$PATH

编辑bash_profile，设置环境变量

vim ~/.bash_profile
export FLUTTER_ROOT=/*你的安装目录*/flutter
export PUB_HOSTED_URL=https://pub.flutter-io.cn
export FLUTTER_STORAGE_BASE_URL=https://storage.flutter-io.cn
export PATH=/*你的安装目录*/flutter/bin:$PATH

运行 flutter doctor
运行以下命令查看是否需要安装其它依赖项来完成安装：

flutter doctor

之后，可能会出现这个问题，flutter dart-sdk下载失败

Downloading Dart SDK from Flutter engine 4e54bc93ca9aaf2156fb06266c9fe509e8599a5f...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:05:00 --:--:--     0
curl: (56) Proxy CONNECT aborted due to timeout

Failed to retrieve the Dart SDK from: https://mirrors.sjtug.sjtu.edu.cn/flutter_infra/flutter/4e54bc93ca9aaf2156fb06266c9fe509e8599a5f/dart-sdk-darwin-x64.zip
If you're located in China, please see this page:
  https://flutter.io/community/china

解决办法：
1、下载dart-sdk：

// 这里的 4e54bc93ca9aaf2156fb06266c9fe509e8599a5f 要跟上面的错误提示显示的一样
wget https://mirrors.sjtug.sjtu.edu.cn/flutter_infra/flutter/4e54bc93ca9aaf2156fb06266c9fe509e8599a5f/dart-sdk-darwin-x64.zip

找到安装目录，我这里是~/development/flutter/，把dart-sdk-darwin-x64.zip放到bin/cache/下，请确保文件名正确。
2、打开/bin/internal/update_dart_sdk.sh文件，注释掉以下行

  rm -rf -- "$DART_SDK_PATH"
  mkdir -m 755 -p -- "$DART_SDK_PATH"
  curl --continue-at - --location --output "$DART_SDK_ZIP" "$DART_SDK_URL" 2>&1 || {
    echo
    echo "Failed to retrieve the Dart SDK from: $DART_SDK_URL"
    echo "If you're located in China, please see this page:"
    echo "  https://flutter.io/community/china"
    echo
    rm -f -- "$DART_SDK_ZIP"
    exit 1
  }