WebClient.DownloadDataCompleted 事件
定義
重要
部分資訊涉及發行前產品,在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊,不做任何明確或隱含的瑕疵擔保。
在非同步資料下載作業完成時發生。
public:
event System::Net::DownloadDataCompletedEventHandler ^ DownloadDataCompleted;
public event System.Net.DownloadDataCompletedEventHandler? DownloadDataCompleted;
public event System.Net.DownloadDataCompletedEventHandler DownloadDataCompleted;
member this.DownloadDataCompleted : System.Net.DownloadDataCompletedEventHandler
Public Custom Event DownloadDataCompleted As DownloadDataCompletedEventHandler
Public Event DownloadDataCompleted As DownloadDataCompletedEventHandler
事件類型
範例
下列程式碼範例示範如何為此事件設定事件處理常式。
// Sample call : DownLoadDataInBackground ("http://www.contoso.com/GameScores.html");
void DownloadDataInBackground( String^ address )
{
System::Threading::AutoResetEvent^ waiter = gcnew System::Threading::AutoResetEvent( false );
WebClient^ client = gcnew WebClient;
Uri ^uri = gcnew Uri(address);
// Specify that the DownloadDataCallback method gets called
// when the download completes.
client->DownloadDataCompleted += gcnew 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 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
下列程式碼範例示範這個事件的處理常式實作。
void DownloadDataCallback( Object^ /*sender*/, DownloadDataCompletedEventArgs^ e )
{
System::Threading::AutoResetEvent^ waiter = dynamic_cast<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 == nullptr )
{
array<Byte>^data = dynamic_cast<array<Byte>^>(e->Result);
String^ textData = System::Text::Encoding::UTF8->GetString( data );
Console::WriteLine( textData );
}
}
finally
{
// Let the main application thread resume.
waiter->Set();
}
}
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
備註
每次非同步資料下載作業完成時,就會引發此事件。 非同步資料下載會藉由呼叫 DownloadDataAsync 方法來啟動。
DownloadDataCompletedEventHandler是這個事件的委派。 類別 DownloadDataCompletedEventArgs 會提供事件處理常式與事件資料。
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
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