WebClient.DownloadFileTaskAsync Method (String, String)

.NET Framework (current version)

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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)]
public 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.

Exception Condition

The address parameter is null.


The fileName parameter is null.


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.

.NET Framework
Available since 4.5
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