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DownloadDataCompletedEventHandler Delegate

Represents the method that will handle the DownloadDataCompleted event of a WebClient.

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

'Declaration
Public Delegate Sub DownloadDataCompletedEventHandler ( _
	sender As Object, _
	e As DownloadDataCompletedEventArgs _
)

Parameters

sender
Type: System.Object

The source of the event.

e
Type: System.Net.DownloadDataCompletedEventArgs

A DownloadDataCompletedEventArgs containing event data.

When you create a DownloadDataCompletedEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event handler delegates, see Events and Delegates.

The following code example demonstrates downloading a user-specified resource.

		'  Sample call : DownLoadDataInBackground ("http:' www.contoso.com/GameScores.html") 
		Public Shared Sub DownloadDataInBackground(ByVal address As String)

			Dim waiter As System.Threading.AutoResetEvent = New System.Threading.AutoResetEvent(False)
			Dim client As WebClient = New WebClient()

			'  Specify that the DownloadDataCallback method gets called 
			'  when the download completes. 
			AddHandler client.DownloadDataCompleted, AddressOf DownloadDataCallback
                        Dim uri as Uri = New Uri(address)
			client.DownloadDataAsync(uri, waiter)

			'  Block the main application thread. Real applications 
			'  can perform other tasks while waiting for the download to complete.
			waiter.WaitOne()
		End Sub

The following method is called when the download completes.

        Private Shared Sub DownloadDataCallback(ByVal sender As Object, ByVal e As DownloadDataCompletedEventArgs)

            Dim waiter As System.Threading.AutoResetEvent = CType(e.UserState, System.Threading.AutoResetEvent)

            Try 

                '  If the request was not canceled and did not throw 
                '  an exception, display the resource. 
                If e.Cancelled = False AndAlso e.Error Is Nothing Then 

                    Dim data() As Byte = CType(e.Result, Byte())
                    Dim textData As String = System.Text.Encoding.UTF8.GetString(data)

                    Console.WriteLine(textData)
                End If 
            Finally 

                '  Let the main application thread resume.
                waiter.Set()
            End Try 
        End Sub

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

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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