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OpenReadTaskAsync Method (String)
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WebClient.OpenReadTaskAsync Method (String)

.NET Framework 4.6 and 4.5

Opens a readable stream containing the specified resource as an asynchronous operation using a task object.

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

<ComVisibleAttribute(False)> _
<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _
Public Function OpenReadTaskAsync ( _
	address As String _
) As Task(Of Stream)


Type: System.String

The URI of the resource to retrieve.

Return Value

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


The address parameter is Nothing.


The URI formed by combining BaseAddress and address is invalid.


An error occurred while downloading the resource.


An error occurred while opening the stream.

This operation will not block. The returned Task(Of TResult) object will complete after the a readable 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 access 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 specify an absolute URI, address must be a relative URI that is combined with BaseAddress to form the absolute URI of the requested resource. If the QueryString property is not Nothing, it is appended to address.

This method uses the RETR command to download an FTP resource. For an HTTP resource, the GET 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