Stream.CopyToAsync Method (Stream)
Asynchronously reads the bytes from the current stream and writes them to another stream.
Assembly: mscorlib (in mscorlib.dll)
'Declaration <ComVisibleAttribute(False)> _ <HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _ Public Function CopyToAsync ( _ destination As Stream _ ) As Task
- Type: System.IO.Stream
The stream to which the contents of the current stream will be copied.
Return ValueType: System.Threading.Tasks.Task
A task that represents the asynchronous copy operation.
The CopyToAsync method enables you to perform resource-intensive I/O operations without blocking the main thread. This performance consideration is particularly important in a Windows Store app or desktop app where a time-consuming stream operation can block the UI thread and make your app appear as if it is not working. The async methods are used in conjunction with the async and await keywords in Visual Basic and C#.
Copying begins at the current position in the current stream.
The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: ExternalThreading. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.
The following example demonstrates how to use two FileStream objects to asynchronously copy the files from one directory to another. The FileStream class derives from the Stream class. Notice that the Click event handler for the Button control is marked with the async modifier because it calls an asynchronous method
Imports System.IO Class MainWindow Private Async Sub Button_Click(sender As Object, e As RoutedEventArgs) Dim StartDirectory As String = "c:\Users\exampleuser\start" Dim EndDirectory As String = "c:\Users\exampleuser\end" For Each filename As String In Directory.EnumerateFiles(StartDirectory) Using SourceStream As FileStream = File.Open(filename, FileMode.Open) Using DestinationStream As FileStream = File.Create(EndDirectory + filename.Substring(filename.LastIndexOf("\"c))) Await SourceStream.CopyToAsync(DestinationStream) End Using End Using Next End Sub End Class