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

.NET Framework (current version)

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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)

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public virtual Task WriteAsync(
	byte[] buffer,
	int offset,
	int count,
	CancellationToken cancellationToken


Type: System.Byte[]

The buffer to write data from.

Type: System.Int32

The zero-based byte offset in buffer from which to begin copying bytes to the stream.

Type: System.Int32

The maximum number of bytes to write.

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 write operation.

Exception Condition

buffer is null.


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 8.x 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 writing.

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(Byte[], Int32, Int32) overload.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.5
Portable Class Library
Supported in: portable .NET platforms
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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