Stream.CopyToAsync Method (Stream, Int32)

.NET Framework 4.5

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

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

[ComVisibleAttribute(false)]
[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public Task CopyToAsync(
	Stream destination,
	int bufferSize
)

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.

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 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.

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: 4.5.2, 4.5.1, 4.5

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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