Stream.WriteAsync Method (array<Byte>[]()[], Int32, Int32, CancellationToken)

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Asynchronously writes a sequence of bytes to the current stream, advances the current position within this stream by the number of bytes written, and monitors cancellation requests.

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


Public Overridable Function WriteAsync ( _
    buffer As Byte(), _
    offset As Integer, _
    count As Integer, _
    cancellationToken As CancellationToken _
) As Task
public virtual Task WriteAsync(
    byte[] buffer,
    int offset,
    int count,
    CancellationToken cancellationToken


  • offset
    Type: System..::.Int32
    The zero-based byte offset in buffer from which to begin copying bytes to the stream.

Return Value

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


Exception Condition

buffer is nullNothingnullptra null reference (Nothing in Visual Basic).


offset or count is negative.


The sum of offset and count is larger than the buffer length.


The stream does not support writing.


The stream has been disposed.


The stream is currently in use by a previous write operation.


The WriteAsync 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#.

Use the CanWrite property to determine whether the current instance supports reading.

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

For an example, see the WriteAsync overload.

Version Information

Windows Phone OS

Supported in: 8.1, 8.0

See Also


Stream Class

WriteAsync Overload

System.IO Namespace

Other Resources