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Stream.CopyToAsync Method (Stream, Int32, CancellationToken)

July 28, 2014

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

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

public virtual Task CopyToAsync(
	Stream destination,
	int bufferSize,
	CancellationToken cancellationToken
)

Parameters

destination
Type: System.IO.Stream
The stream to which the contents of the current stream will be copied.
bufferSize
Type: System.Int32
The size, in bytes, of the buffer. This value must be greater than zero. The default size is 4096.
cancellationToken
Type: System.Threading.CancellationToken
The token to monitor for cancellation requests. The default value is None.

Return Value

Type: System.Threading.Tasks.Task
A task that represents the asynchronous copy operation.

ExceptionCondition
ArgumentNullException

destination is null.

ArgumentOutOfRangeException

buffersize is negative or zero.

ObjectDisposedException

Either the current stream or the destination stream is disposed.

NotSupportedException

The current stream does not support reading, or the destination stream does not support writing.

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 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#.

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

Copying begins at the current position in the current stream.

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

Windows Phone OS

Supported in: 8.1, 8.0

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