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Stream::CopyToAsync Method (Stream, Int32, CancellationToken)

.NET Framework 4.5

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)

[ComVisibleAttribute(false)]
[HostProtectionAttribute(SecurityAction::LinkDemand, ExternalThreading = true)]
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 81920.

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 nullptr.

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 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(Stream) overload.

NoteNote

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.

.NET Framework

Supported in: 4.6, 4.5

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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