WebClient UploadString（url，data）方法丢失“Content-Type”/“application / json”调用后的标题。 [英] WebClient UploadString(url, data) Method Loses "Content-Type"/"application/json" Header After Invocation.

问题描述

大家好！

我注意到 after I调用WebClient UploadString（url，data）方法，WebClient"丢失"。的 "内容类型" /"应用/ JSON"标题，但不是 "" api_key"，
"< api_key>" 。报头NBSP;如果我选择重复使用WebClient，我需要检查 "Content-Type"/" application / json"标题存在并再次添加
，然后再调用 调用WebClient UploadString（url，data）方法。

I have noticed that after I invoke the WebClient UploadString(url, data) method, the WebClient "loses" the "Content-Type"/"application/json" header, but not the "api_key", "<api_key>" header.  If I choose to reuse the WebClient, I need to check if the "Content-Type"/"application/json" header is present and add it again before invoking the WebClient UploadString(url, data) method.

                if (!webClient.Headers.AllKeys.Contains("Content-Type"))
                {
                    webClient.Headers.Add("Content-Type", "application/json");
                }

                var response = webClient.UploadString(url, data);

有没有解释？

Is there an explanation for that?

推荐答案

这在
WebClient.Headers 的文档中提到（"你不应该假设标题值将保持不变，因为Web服务器和缓存可能会更改或添加标头到Web请求""，并且可以在源代码中看到：

https://referencesource.microsoft.com/#System/net/System/Net /webclient.cs,6fa3cb436d1d0456 。可能有一些原因，可能是为了简化将标题转移到其他对象。

This is mentioned in documentation for WebClient.Headers ("You should not assume that the header values will remain unchanged, because Web servers and caches may change or add headers to a Web request") and can be seen in the sources: https://referencesource.microsoft.com/#System/net/System/Net/webclient.cs,6fa3cb436d1d0456. Probably there were some reasons, maybe to simplify transferring the headers to other objects.

顺便说一句，试试一个更简单的
webClient.Headers [" Content-Type"] = "application / json"没有
如果。

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