WebClient.DownloadStringCompleted 事件

定义

命名空间:

System.Net

程序集:

System.Net.WebClient.dll

Source:

WebClient.cs

异步资源下载操作完成时发生。

public:
 event System::Net::DownloadStringCompletedEventHandler ^ DownloadStringCompleted;

public event System.Net.DownloadStringCompletedEventHandler? DownloadStringCompleted;

member this.DownloadStringCompleted : System.Net.DownloadStringCompletedEventHandler 

Public Custom Event DownloadStringCompleted As DownloadStringCompletedEventHandler 

事件类型

DownloadStringCompletedEventHandler

示例

下面的代码示例演示如何为此事件设置事件处理程序。

// Sample call : DownloadStringInBackground2 ("http://www.contoso.com/GameScores.html");
void DownloadStringInBackground2( String^ address )
{
   WebClient^ client = gcnew WebClient;
   Uri ^uri = gcnew Uri(address);

   // Specify that the DownloadStringCallback2 method gets called
   // when the download completes.
   client->DownloadStringCompleted += gcnew DownloadStringCompletedEventHandler( DownloadStringCallback2 );
   client->DownloadStringAsync( uri );
}

// Sample call : DownloadStringInBackground2 ("http://www.contoso.com/GameScores.html");
public static void DownloadStringInBackground2(string address)
{
    WebClient client = new WebClient();
    Uri uri = new Uri(address);

    // Specify that the DownloadStringCallback2 method gets called
    // when the download completes.
    client.DownloadStringCompleted += new DownloadStringCompletedEventHandler(DownloadStringCallback2);
    client.DownloadStringAsync(uri);
}

'  Sample call : DownloadStringInBackground2 ("http:' www.contoso.com/GameScores.html")
Public Shared Sub DownloadStringInBackground2(ByVal address As String)

    Dim client As WebClient = New WebClient()

    '  Specify that the DownloadStringCallback2 method gets called
    '  when the download completes.
    AddHandler client.DownloadStringCompleted, AddressOf DownloadStringCallback2
                Dim uri as Uri = New Uri(address)
    client.DownloadStringAsync(uri)
End Sub

下面的代码示例演示此事件的处理程序的实现。

void DownloadStringCallback2( Object^ /*sender*/, DownloadStringCompletedEventArgs^ e )
{

   // If the request was not canceled and did not throw
   // an exception, display the resource.
   if (  !e->Cancelled && e->Error == nullptr )
   {
      String^ textString = dynamic_cast<String^>(e->Result);
      Console::WriteLine( textString );
   }
}

private static void DownloadStringCallback2(Object sender, DownloadStringCompletedEventArgs e)
{
    // If the request was not canceled and did not throw
    // an exception, display the resource.
    if (!e.Cancelled && e.Error == null)
    {
        string textString = (string)e.Result;

        Console.WriteLine(textString);
    }
}

Private Shared Sub DownloadStringCallback2(ByVal sender As Object, ByVal e As DownloadStringCompletedEventArgs)

    '  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 textString As String = CStr(e.Result)
        Console.WriteLine(textString)
    End If
End Sub

注解

谨慎

WebRequest、HttpWebRequest、ServicePoint和 WebClient 已过时，不应将其用于新开发。 请改用 HttpClient。

每次异步操作以字符串的形式下载资源时都会引发此事件。 这些操作通过调用 DownloadStringAsync 方法启动。

DownloadStringCompletedEventHandler 是此事件的委托。 DownloadStringCompletedEventArgs 类为事件处理程序提供事件数据。

有关如何处理事件的详细信息，请参阅 处理和引发事件。