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WebClient::DownloadFileTaskAsync Method (String, String)

.NET Framework 4.6 and 4.5

Downloads the specified resource to a local file as an asynchronous operation using a task object.

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

[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
Task^ DownloadFileTaskAsync(
	String^ address, 
	String^ fileName


Type: System::String

The URI of the resource to download.

Type: System::String

The name of the file to be placed on the local computer.

Return Value

Type: System.Threading.Tasks::Task
Returns Task.
The task object representing the asynchronous operation.


The address parameter is nullptr.


The fileName parameter is nullptr.


The URI formed by combining BaseAddress and address is invalid.


An error occurred while downloading the resource.


The local file specified by fileName is in use by another thread.

This operation will not block. The returned Task object will complete after the data resource has been downloaded.

This method downloads the resource at the URI specified by in the address parameter. When the download completes successfully, the downloaded file is named fileName on the local computer. The file is downloaded asynchronously using thread resources that are automatically allocated from the thread pool.

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 specify 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.


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

When using this method in an ASP.NET page, you will receive an error if the account that the page executes under does not have permission to access the local file.


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