WebClient.DownloadDataAsync Method (Uri) (System.Net)

.NET Framework Class Library

WebClient..::.DownloadDataAsync Method (Uri)

Downloads the specified resource as a Byte array. This method does not block the calling thread.

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

Syntax

Visual Basic (Declaration)

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _
Public Sub DownloadDataAsync ( _
    address As Uri _
)

Visual Basic (Usage)

Dim instance As WebClient
Dim address As Uri

instance.DownloadDataAsync(address)

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public void DownloadDataAsync(
    Uri address
)

Visual C++

[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
public:
void DownloadDataAsync(
    Uri^ address
)

JScript

public function DownloadDataAsync(
    address : Uri
)

Parameters

address: Type: System..::.Uri
A Uri containing the URI to download.

Exceptions

Exception	Condition
WebException	The URI formed by combining BaseAddress and address is invalid. -or- An error occurred while downloading the resource.

Exception

Condition

WebException

The URI formed by combining BaseAddress and address is invalid.

-or-

An error occurred while downloading the resource.

Remarks

Note:
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.

Note:

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.

This method retrieves the specified resource using the default method for the protocol associated with the URI scheme specified in address. The data is downloaded asynchronously using thread resources that are automatically allocated from the thread pool.

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 one of the DownloadData methods. When the download completes, the DownloadDataCompleted event is raised. Your application must handle this event to receive notification. The downloaded data is available in the Result property.

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

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

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.

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

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

Reference

WebClient Class

WebClient Members

DownloadDataAsync Overload

System.Net Namespace