Stream.CopyToAsync Method (Stream)
Asynchronously reads the bytes from the current stream and writes them to another stream.
Assembly: mscorlib (in mscorlib.dll)
[<ComVisibleAttribute(false)>] [<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)>] member CopyToAsync : destination:Stream -> 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.
destination is a null reference (Nothing in Visual Basic).
Either the current stream or the destination stream is disposed.
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.
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
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.