feature：complete niupic image upload

Author: hackycy

lib/api/niupic_api.dart

@@ -0,0 +1,12 @@
+import 'package:dio/dio.dart';
+import 'package:flutter_picgo/utils/net.dart';
+
+class NiupicApi {
+  static const BASE_URL = 'https://www.niupic.com/';
+
+  static Future upload(FormData data) async {
+    Response res = await NetUtils.getInstance()
+        .post(BASE_URL + 'index/upload/process', data: data);
+    return res.data;
+  }
+}

lib/utils/strategy/impl/niupic_image_upload.dart

@@ -0,0 +1,53 @@
+import 'package:dio/dio.dart';
+import 'package:flutter_picgo/api/niupic_api.dart';
+import 'package:flutter_picgo/model/uploaded.dart';
+import 'package:flutter_picgo/resources/pb_type_keys.dart';
+import 'package:flutter_picgo/utils/image_upload.dart';
+import 'dart:io';
+
+import 'package:flutter_picgo/utils/strategy/image_upload_strategy.dart';
+
+class NiupicImageUpload implements ImageUploadStrategy {
+  /// 牛图网不支持删除
+  @override
+  Future<Uploaded> delete(Uploaded uploaded) async {
+    return uploaded;
+  }
+
+  @override
+  Future<Uploaded> upload(File file, String renameImage) async {
+    FormData formData = FormData.fromMap({
+      "image_field":
+          await MultipartFile.fromFile(file.path, filename: renameImage),
+    });
+    var result = await NiupicApi.upload(formData);
+    if (result["code"] == 200) {
+      var uploadedItem = Uploaded(
+          -1, 'https://${result['data']}', PBTypeKeys.niupic,
+          info: '');
+      await ImageUploadUtils.saveUploadedItem(uploadedItem);
+      return uploadedItem;
+    } else {
+      throw new NiupicError(error: '${result['msg']}');
+    }
+  }
+}
+
+class NiupicError implements Exception {
+  NiupicError({
+    this.error,
+  });
+
+  dynamic error;
+
+  String get message => (error?.toString() ?? '');
+
+  @override
+  String toString() {
+    var msg = 'NiupicError $message';
+    if (error is Error) {
+      msg += '\n${error.stackTrace}';
+    }
+    return msg;
+  }
+}

lib/utils/strategy/upload_strategy_factory.dart

@@ -3,6 +3,7 @@ import 'package:flutter_picgo/utils/strategy/impl/aliyun_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/impl/gitee_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/impl/github_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/image_upload_strategy.dart';
+import 'package:flutter_picgo/utils/strategy/impl/niupic_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/impl/qiniu_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/impl/smms_image_upload.dart';
 import 'package:flutter_picgo/utils/strategy/impl/tcyun_image_upload.dart';
@@ -35,6 +36,9 @@ class UploadStrategyFactory {
       } else if (type == PBTypeKeys.tcyun) {
         /// 腾讯云
         cache[type] = new TcyunImageUpload();
+      } else if (type == PBTypeKeys.niupic) {
+        /// 牛图网
+        cache[type] = new NiupicImageUpload();
       }
     }
     return cache[type];