DownloadDataCompletedEventHandler Делегат

Определение

public delegate void DownloadDataCompletedEventHandler(System::Object ^ sender, DownloadDataCompletedEventArgs ^ e);

public delegate void DownloadDataCompletedEventHandler(object sender, DownloadDataCompletedEventArgs e);

type DownloadDataCompletedEventHandler = delegate of obj * DownloadDataCompletedEventArgs -> unit

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

Параметры

Примеры

В следующем примере кода демонстрируется скачивание ресурса, указанного пользователем.

// Sample call : DownLoadDataInBackground ("http://www.contoso.com/GameScores.html");
public static void DownloadDataInBackground(string address)
{
    System.Threading.AutoResetEvent waiter = new System.Threading.AutoResetEvent(false);
    WebClient client = new WebClient();
    Uri uri = new Uri(address);

    // Specify that the DownloadDataCallback method gets called
    // when the download completes.
    client.DownloadDataCompleted += new DownloadDataCompletedEventHandler(DownloadDataCallback);
    client.DownloadDataAsync(uri, waiter);

    // Block the main application thread. Real applications
    // can perform other tasks while waiting for the download to complete.
    waiter.WaitOne();
}

'  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

Следующий метод вызывается по завершении скачивания.

private static void DownloadDataCallback(Object sender, DownloadDataCompletedEventArgs e)
{
    System.Threading.AutoResetEvent waiter = (System.Threading.AutoResetEvent)e.UserState;

    try
    {
        // If the request was not canceled and did not throw
        // an exception, display the resource.
        if (!e.Cancelled && e.Error == null)
        {
            byte[] data = (byte[])e.Result;
            string textData = System.Text.Encoding.UTF8.GetString(data);

            Console.WriteLine(textData);
        }
    }
    finally
    {
        // Let the main application thread resume.
        waiter.Set();
    }
}

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

Комментарии

При создании делегата DownloadDataCompletedEventHandler необходимо указать метод, обрабатывающий событие. Чтобы связать событие с обработчиком событий, нужно добавить в событие экземпляр делегата. Обработчик событий вызывается всякий раз, когда происходит событие, если делегат не удален. Дополнительные сведения о делегатах обработчика событий см. в разделе Обработка и вызов событий.