问题
How I can set a header in the webClient class?
I tried:
client.Headers["Content-Type"] = "image/jpeg";
that throws a WebException
My code:
WebClient client = new WebClient();
client.Headers.Set("Content-Type", "image/png");
client.Headers.Set("Content-Length", length);
client.Headers.Add("Slug", name);
NameValueCollection nvc = new NameValueCollection();
nvc.Add("file", FileContents);
Byte[] data = client.UploadValues(url, nvc);
string res = Encoding.ASCII.GetString(data);
Response.Write(res);
回答1:
If the header already exists:
client.Headers.Set("Content-Type", "image/jpeg");
if its a new header:
client.Headers.Add("Content-Type", "image/jpeg");
Also, there is a chance that you are getting an error because you are trying to set the headers too late. Post your exception so we can let you know.
Update
Looks like there are some weird restrictions on the "Content-Type" header with the WebClient class. Look in to using the client.Download methods (DownloadData, DownloadFile, etc...)
See if using the "UploadFile" method on webclient works rather than doing it manually. It returns the respose body byte[].
If you continue to have issues with the WebClient, try justing using a plain old HttpRequest/HttpWebRequest.
回答2:
It seems you can not set Content-type with WebClient.UploadValues method. You could set Content-type with WebClient.UploadData method
Use something like,
Client.Headers["Content-Type"] = "application/json";
Client.UploadData("http://www.imageshack.us/upload_api.php", "POST", Encoding.Default.GetBytes("{\"Data\": \"Test\"}"));
回答3:
You cannot change the Content-Type if you use the UploadValues method, it must be application/x-www-form-urlencoded, see webclient source code
回答4:
Have you tried this syntax: client.Headers.Add("Content-Type", "image/jpeg");
What's your stack trace? At what point are you setting this? And what version of IIS/OS are you running under?
来源：https://stackoverflow.com/questions/6560769/webclient-set-headers