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WebClient.DownloadStringAsync Method (Uri, Object)

Downloads the specified string to the specified resource. This method does not block the calling thread.

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

[<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>]
member DownloadStringAsync : 
        address:Uri * 
        userToken:Object -> unit

Parameters

address
Type: System.Uri

A Uri containing the URI to download.

userToken
Type: System.Object

A user-defined object that is passed to the method invoked when the asynchronous operation completes.

ExceptionCondition
ArgumentNullException

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

WebException

The URI formed by combining BaseAddress and address is invalid.

-or-

An error occurred while downloading the resource.

The resource is downloaded asynchronously using thread resources that are automatically allocated from the thread pool.

After downloading the resource, this method uses the encoding specified in the Encoding property to convert the resource to a String. This method does not block the calling thread while downloading the resource. To download a resource and block while waiting for the server's response, use the DownloadString method. When the download completes, the DownloadStringCompleted event is raised. Your application must handle this event to receive notification. The downloaded string is available in the Result property.

You can use the CancelAsync method to cancel asynchronous operations that have not completed.

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 RETR command to download an FTP resource. For an HTTP resource, the GET method is used.

NoteNote

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

NoteNote

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: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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