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OpenWriteTaskAsync Method (Uri)

WebClient.OpenWriteTaskAsync Method (Uri)

.NET Framework 4.6 and 4.5

Opens a stream for writing data to the specified resource as an asynchronous operation using a task object.

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

[<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>]
member OpenWriteTaskAsync : 
        address:Uri -> Task<Stream> 


Type: System.Uri

The URI of the resource to receive the data.

Return Value

Type: System.Threading.Tasks.Task(Stream)
Returns Task(TResult).
The task object representing the asynchronous operation. The Result property on the task object returns a Stream used to write data to the resource.


The address parameter is a null reference (Nothing in Visual Basic).


The URI formed by combining BaseAddress and address is invalid.


An error occurred while opening the stream.

This operation will not block. The returned Task(TResult) object will complete after the a writable stream to the data resource has been opened. This method does not block the calling thread while the stream is opening.

This method retrieves a Stream instance used to write data to the resource specified by the address parameter. The stream is obtained using thread resources that are automatically allocated from the thread pool.


You must call Stream.Close when you are finished with the Stream to avoid running out of system resources.

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

If the BaseAddress property is not an empty string ("") and address does not contain an absolute URI, 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 in the .NET Framework.


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: 4.6, 4.5
© 2015 Microsoft