flutter 图片上传 cos

费了半天劲，先说一下遇到的几个坑：

1、cos拼接目录两边要带‘/’ 不然会报签名不匹配

'/picture/'获取签名和文件上传需要使用

2、flutter 热重载 静态变量无法重置需要重启或重新打开应用

3、cos http协议put请求

一、选择图片：

使用插件 image_picker: '^0.4.5'

import 'package:image_picker/image_picker.dart';

ImagePicker.pickImage(source: source);

相机：ImageSource.camera

图库：ImageSource.gallery

选择完后回调：

 body: new FutureBuilder(
        future: _imageFile,
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.connectionState == ConnectionState.done &&
              snapshot.data != null &&
              _imageFile != null) {
            fileList.add(snapshot.data);
            upimg(snapshot.data);
            _imageFile = null;
          }
          return getBody();
        },
      ),

二、上传图片

upimg(File f) {
    var filename = f.path.substring(f.path.lastIndexOf("/") + 1);
    String key = '${new DateTime.now().millisecondsSinceEpoch}$filename';
    key = imgDir + key;
    DataUtils.tokenHttp(
            Api.getSign, {'method': 'PUT', 'pathname': key}, context)
        .then((val) async {
      try {
        Map params = new Map();
        params['Authorization'] = val['data'];
        List bytes = await f.readAsBytes();
        http
            .put(Api.prefix + key, headers: params, body: bytes)
            .then((response) {
          print(response);
        });
      } catch (exception) {
        print(exception);
      }
      print(val);
    });
  }