FileStream.CopyToAsync(Stream, Int32, CancellationToken) Method


Asynchronously reads the bytes from the current file stream and writes them to another stream, using a specified buffer size and cancellation token.

 override System::Threading::Tasks::Task ^ CopyToAsync(System::IO::Stream ^ destination, int bufferSize, System::Threading::CancellationToken cancellationToken);
public override System.Threading.Tasks.Task CopyToAsync (System.IO.Stream destination, int bufferSize, System.Threading.CancellationToken cancellationToken);
override this.CopyToAsync : System.IO.Stream * int * System.Threading.CancellationToken -> System.Threading.Tasks.Task
Public Overrides Function CopyToAsync (destination As Stream, bufferSize As Integer, cancellationToken As CancellationToken) As Task



The stream to which the contents of the current file stream will be copied.


The size, in bytes, of the buffer. This value must be greater than zero. The default size is 81920.


The token to monitor for cancellation requests. The default value is None.



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 8.x 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#.

If the operation is canceled before it completes, the returned task contains the TaskStatus.Canceled value for the Task.Status property.

Copying begins at the current position in the current file stream.

For an example of copying between two streams, see the CopyToAsync(Stream) overload.

Applies to