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I am using WebClient.UploadFileAsync to upload local files to a web server and I would also like to pass some parameters with the post as well. I would like to send a few fields that will tell the PHP code on the server specific locations on where to save the uploaded files.

I tried to put the fields directly into the url, for example:

WebClient client = new WebClient();
Uri uri = new Uri("http://example.com/upload.php?field1=test");
client.UploadFileAsync(uri, "POST", "c:\test.jpg");

The PHP code returns false for isset($_REQUEST['field1']).

Thank you for any suggestions.

NOTE: this question was also asked in very similar format for vb.net a while back, but it did not get any answers,

Community
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Keith Maurino
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3 Answers3

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WebClient's UploadFile is designed to send only a file (as byte[]) as part of request. From my understanding, UploadFile method closes the request stream after writing the binaries.

In your scenario, you actually request is has two parts 1. file as byte[] 2. the file name as string.

To do this, you have to use HttpWebRequest or any other high level class capable of creating request.

Refer to the post http://www.codeproject.com/KB/cs/uploadfileex.aspx?display=Print which does a similar job

humblelistener
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This article goes into detail about what is needed to accomplish posting of fields while uploading files using WebClient.

Unfortunately, most file upload scenarios are HTML form based and may contain form fields in addition to the file data. This is where WebClient falls flat. After review of the source code for WebClient, it is obvious that there is no possibility of reusing it to perform a file upload including additional form fields.

So, the only option is to create a custom implementation that conforms to rfc1867, rfc2388 and the W3C multipart/form-data specification that will enable file upload with additional form fields and exposes control of cookies and headers.

Keith Maurino
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I would look into using the QueryString property of the WebClient to set the value of field1 (as well as any other QueryString parameters to the request).

NameValueCollection query = new NameValueCollection();
query.Add("field1", "test");
client.QueryString = query;

Reference: http://msdn.microsoft.com/en-us/library/system.net.webclient.querystring(v=VS.100).aspx

rtalbot
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