WebClient.DownloadProgressChanged Evento

Definizione

Si verifica quando un'operazione asincrona di download trasferisce correttamente alcuni o tutti i dati.Occurs when an asynchronous download operation successfully transfers some or all of the data.

public:
 event System::Net::DownloadProgressChangedEventHandler ^ DownloadProgressChanged;
public event System.Net.DownloadProgressChangedEventHandler DownloadProgressChanged;
member this.DownloadProgressChanged : System.Net.DownloadProgressChangedEventHandler 
Public Event DownloadProgressChanged As DownloadProgressChangedEventHandler 

Esempi

Nell'esempio di codice riportato di seguito viene illustrata l'impostazione di un gestore eventi per questo evento.The following code example demonstrates setting an event handler for this event.

// Sample call : DownLoadFileInBackground2 ("http://www.contoso.com/logs/January.txt");
void DownLoadFileInBackground2( String^ address )
{
   WebClient^ client = gcnew WebClient;
   Uri ^uri = gcnew Uri(address);
   
   // Specify that the DownloadFileCallback method gets called
   // when the download completes.
   client->DownloadFileCompleted += gcnew AsyncCompletedEventHandler( DownloadFileCallback2 );
   
   // Specify a progress notification handler.
   client->DownloadProgressChanged += gcnew DownloadProgressChangedEventHandler( DownloadProgressCallback );
   client->DownloadFileAsync( uri, "serverdata.txt" );
}


// Sample call : DownLoadFileInBackground2 ("http://www.contoso.com/logs/January.txt");
public static void DownLoadFileInBackground2 (string address)
{
    WebClient client = new WebClient ();
    Uri uri = new Uri(address);

    // Specify that the DownloadFileCallback method gets called
    // when the download completes.
    client.DownloadFileCompleted += new AsyncCompletedEventHandler (DownloadFileCallback2);
    // Specify a progress notification handler.
    client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(DownloadProgressCallback);
    client.DownloadFileAsync (uri, "serverdata.txt");
}

'  Sample call : DownLoadFileInBackground2 ("http:' www.contoso.com/logs/January.txt")
Public Shared Sub DownLoadFileInBackground2(ByVal address As String)

    Dim client As WebClient = New WebClient()

    '  Specify that the DownloadFileCallback method gets called
    '  when the download completes.
    AddHandler client.DownloadFileCompleted, AddressOf DownloadFileCallback2
    '  Specify a progress notification handler.
    AddHandler client.DownloadProgressChanged, AddressOf DownloadProgressCallback
                Dim uri as Uri = New Uri(address)
    client.DownloadFileAsync(uri, "serverdata.txt")
End Sub

Nell'esempio di codice seguente viene illustrata un'implementazione di un gestore per questo evento.The following code example shows an implementation of a handler for this event.

static void UploadProgressCallback(Object^ sender, 
          UploadProgressChangedEventArgs^ e)
      {
          // Displays the operation identifier, and the transfer progress.
          Console::WriteLine("{0}    uploaded {1} of {2} bytes. {3} % complete...", 
              (String ^)e->UserState, 
              e->BytesSent, 
              e->TotalBytesToSend,
              e->ProgressPercentage);
      }
static void DownloadProgressCallback(Object^ sender, 
          DownloadProgressChangedEventArgs^ e)
      {
          // Displays the operation identifier, and the transfer progress.
          Console::WriteLine("{0}    downloaded {1} of {2} bytes. {3} % complete...", 
              (String ^)e->UserState, 
              e->BytesReceived, 
              e->TotalBytesToReceive,
              e->ProgressPercentage);
      }
private static void UploadProgressCallback(object sender, UploadProgressChangedEventArgs e)
{
    // Displays the operation identifier, and the transfer progress.
    Console.WriteLine("{0}    uploaded {1} of {2} bytes. {3} % complete...", 
        (string)e.UserState, 
        e.BytesSent, 
        e.TotalBytesToSend,
        e.ProgressPercentage);
}
private static void DownloadProgressCallback(object sender, DownloadProgressChangedEventArgs e)
{
    // Displays the operation identifier, and the transfer progress.
    Console.WriteLine("{0}    downloaded {1} of {2} bytes. {3} % complete...", 
        (string)e.UserState, 
        e.BytesReceived, 
        e.TotalBytesToReceive,
        e.ProgressPercentage);
}
Private Shared Sub UploadProgressCallback(ByVal sender As Object, ByVal e As UploadProgressChangedEventArgs)

    '  Displays the operation identifier, and the transfer progress.
    Console.WriteLine("{0}    uploaded {1} of {2} bytes. {3} % complete...", _
     CStr(e.UserState), e.BytesSent, e.TotalBytesToSend, e.ProgressPercentage)
End Sub
Private Shared Sub DownloadProgressCallback(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs)

    '  Displays the operation identifier, and the transfer progress.
    Console.WriteLine("0}    downloaded 1} of 2} bytes. 3} % complete...", _
     CStr(e.UserState), e.BytesReceived, e.TotalBytesToReceive, e.ProgressPercentage)
End Sub

Commenti

Questo evento viene generato ogni volta che si esegue un download asincrono.This event is raised each time an asynchronous download makes progress. Questo evento viene generato quando i download vengono avviati utilizzando uno dei metodi seguenti.This event is raised when downloads are started using any of the following methods.

MetodoMethod DescriptionDescription
DownloadDataAsync Scarica i dati da una risorsa e restituisce una matrice Byte, senza bloccare il thread chiamante.Downloads data from a resource and returns a Byte array, without blocking the calling thread.
DownloadFileAsync Scarica i dati da una risorsa in un file locale senza bloccare il thread chiamante.Downloads data from a resource to a local file, without blocking the calling thread.
OpenReadAsync Restituisce i dati di una risorsa, senza bloccare il thread chiamante.Returns the data from a resource, without blocking the calling thread.

Il DownloadProgressChangedEventHandler è il delegato per questo evento.The DownloadProgressChangedEventHandler is the delegate for this event. La classe DownloadProgressChangedEventArgs fornisce il gestore eventi con i dati dell'evento.The DownloadProgressChangedEventArgs class provides the event handler with event data.

Per altre informazioni su come gestire gli eventi, vedere la gestione e generazione di eventi.For more information about how to handle events, see Handling and Raising Events.

Nota

Un trasferimento di file FTP passivo indicherà sempre una percentuale di avanzamento pari a zero, poiché il server non ha inviato le dimensioni del file.A passive FTP file transfer will always show a progress percentage of zero, since the server did not send the file size. Per visualizzare lo stato di avanzamento, è possibile impostare la connessione FTP su Active eseguendo l'override del metodo virtuale GetWebRequest:To show progress, you can change the FTP connection to active by overriding the GetWebRequest virtual method:

internal class MyWebClient : WebClient
{  
    protected override WebRequest GetWebRequest(Uri address)
    {  
        FtpWebRequest req = (FtpWebRequest)base.GetWebRequest(address);  
        req.UsePassive = false;  
        return req;  
    }  
}  

Si applica a