WebClient.OpenReadTaskAsync Method (String)

.NET Framework (current version)

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

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

<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.

Exception Condition

The address parameter is null.


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 null, 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.

.NET Framework
Available since 4.5
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