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WebClient::UploadFileAsync Method (Uri, String, String, Object)

Uploads the specified local file to the specified resource, using the POST method. This method does not block the calling thread.

Namespace:  System.Net
Assembly:  System (in System.dll)

[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
void UploadFileAsync(
	Uri^ address, 
	String^ method, 
	String^ fileName, 
	Object^ userToken


Type: System::Uri
The URI of the resource to receive the file. For HTTP resources, this URI must identify a resource that can accept a request sent with the POST method, such as a script or ASP page.
Type: System::String
The HTTP method used to send the data to the resource. If null, the default is POST for http and STOR for ftp.
Type: System::String
The file to send to the resource.
Type: System::Object
A user-defined object that is passed to the method invoked when the asynchronous operation completes.


The address parameter is nullptr.


The fileName parameter is nullptr.


The URI formed by combining BaseAddress and address is invalid.


fileName is nullptr, is Empty, contains invalid character, or the specified path to the file does not exist.


An error occurred while opening the stream.


There was no response from the server hosting the resource.


The Content-type header begins with multipart.

The file is sent asynchronously using thread resources that are automatically allocated from the thread pool. To receive notification when the file upload completes, add an event handler to the UploadFileCompleted event.

This method does not block the calling thread while the file is being sent. To send a file and block while waiting for the server's response, use one of the UploadFile methods.

Asynchronous operations that have not completed can be canceled using the CancelAsync method.

If the BaseAddress property is not an empty string (""), address must be a relative URI that is combined with BaseAddress to form the absolute URI of the requested data. If the QueryString property is not an empty string, it is appended to address.

This method uses the STOR command to upload an FTP resource. For an HTTP resource, the POST method is used.


This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.