WebApi，WebNet 接收Jsonp

本随笔为文章转载，勿笑

第一步：

创建JsonpMediaTypeFormatter 

 public class JsonpMediaTypeFormatter : JsonMediaTypeFormatter
    {
        public string Callback { get; private set; }

        public JsonpMediaTypeFormatter(string callback = null)
        {
            this.Callback = callback;
        }

        public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
        {
            if (string.IsNullOrEmpty(this.Callback))
            {
                return base.WriteToStreamAsync(type, value, writeStream, content, transportContext);
            }
            try
            {
                this.WriteToStream(type, value, writeStream, content);
                return Task.FromResult<AsyncVoid>(new AsyncVoid());
            }
            catch (Exception exception)
            {
                TaskCompletionSource<AsyncVoid> source = new TaskCompletionSource<AsyncVoid>();
                source.SetException(exception);
                return source.Task;
            }
        }

        private void WriteToStream(Type type, object value, Stream writeStream, HttpContent content)
        {
            JsonSerializer serializer = JsonSerializer.Create(this.SerializerSettings);
            using (StreamWriter streamWriter = new StreamWriter(writeStream, this.SupportedEncodings.First()))
            using (JsonTextWriter jsonTextWriter = new JsonTextWriter(streamWriter) { CloseOutput = false })
            {
                jsonTextWriter.WriteRaw(this.Callback + "(");
                serializer.Serialize(jsonTextWriter, value);
                jsonTextWriter.WriteRaw(")");
            }
        }

        public override MediaTypeFormatter GetPerRequestFormatterInstance(Type type, HttpRequestMessage request, MediaTypeHeaderValue mediaType)
        {
            if (request.Method != HttpMethod.Get)
            {
                return this;
            }
            string callback;
            if (request.GetQueryNameValuePairs().ToDictionary(pair => pair.Key,
                 pair => pair.Value).TryGetValue("callback", out callback))
            {
                return new JsonpMediaTypeFormatter(callback);
            }
            return this;
        }

        [StructLayout(LayoutKind.Sequential, Size = 1)]
        private struct AsyncVoid
        { }
    }

第二步：

Global.asax添加以下代码

protected void Application_Start()
        {
　　　　　　　//返回Json时使用
            GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();
            
            //设置Jsonp格式序列化方法
            GlobalConfiguration.Configuration.Formatters.Insert(0, new JsonpMediaTypeFormatter());

            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }