WebClient.DownloadDataCompleted 事件

定義

命名空間:

System.Net

組件:

netstandard.dll, System.Net.WebClient.dll

來源:

WebClient.cs

發生於異步數據下載作業完成時。

C#

public event System.Net.DownloadDataCompletedEventHandler? DownloadDataCompleted;

事件類型

DownloadDataCompletedEventHandler

範例

下列程式代碼範例示範如何設定此事件的事件處理程式。

C#

// 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();
}

下列程式代碼範例示範此事件的處理程序實作。

C#

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();
    }
}

備註

注意

WebRequest、HttpWebRequest、ServicePoint和 WebClient 已經過時，您不應該將它們用於新的開發。 請改用 HttpClient。

每次異步數據下載作業完成時，都會引發此事件。 異步數據下載的啟動方式是呼叫 DownloadDataAsync 方法。

DownloadDataCompletedEventHandler 是這個事件的委派。 DownloadDataCompletedEventArgs 類別會提供事件處理程式與事件數據。

如需如何處理事件的詳細資訊，請參閱 處理和引發事件。

適用於