使用 Flutter 和 Dio 将图像上传到 API

如何将图片以字符串格式发送给API？这是在多部分文件实例中发送数据但data['avatar']接受字符串的代码.那么我该怎么做呢？请帮我拿一下这个.

static Future<Response> updateUserAccount({
    XFile? avatar,
    String? fullName,
    String? email,
    String? oldPhone,
    String? phone,
    String? city,
    String? streetName,
    String? landmark,
    String? oldPassword,
    String? password,
  }) async {
    final dio = Dio();
    String token = await SecureStorageUtils.getToken();
    dio.options.headers['accept'] = '*/*';
    dio.options.headers['content-type'] = 'multipart/form-data';
    dio.options.headers['authorization'] = 'Bearer $token';
    Map<String, dynamic> data = {};
    if (avatar != null) {
      data['avatar'] = await MultipartFile.fromFile(avatar.path);
    }

    if (email != null) {
      data['email'] = email;
    }

    if (oldPhone != null) {
      data['old_phone_number'] = oldPhone;
    }

    if (phone != null) {
      data['phone_number'] = phone;
    }

    if (city != null || streetName != null || landmark != null) {
      final address = {};

      if (city != null) {
        address['city'] = city;
      }

      if (streetName != null) {
        address['street_name'] = streetName;
      }

      if (landmark != null) {
        address['landmark'] = landmark;
      }
      data['address'] = address;
    }

    if (oldPassword != null) {
      data['old_password'] = oldPassword;
    }
    if (password != null) {
      data['password'] = password;
    }
    if (fullName != null) {
      data['full_name'] = fullName;
    }
    print("data: $data");

    FormData formData = FormData.fromMap(data);

    final response = await dio.patch(
      AppUrl.currentUser,
      data: formData,
    );
    return response;
  }

我使用Base64Endingtry 了这种方法，但它不起作用.

List<int> fileBytes = await avatar.readAsBytes();
  String base64Avatar = base64Encode(fileBytes);
  data['avatar'] = base64Avatar;