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

.NET Framework 4.5

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)

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

Parameters

buffer
Type: System.Byte[]

The buffer to write data from.

offset
Type: System.Int32

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

count
Type: System.Int32

The maximum number of bytes to write.

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 write operation.

ExceptionCondition
ArgumentNullException

buffer is null.

ArgumentOutOfRangeException

offset or count is negative.

ArgumentException

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

NotSupportedException

The stream does not support writing.

ObjectDisposedException

The stream has been disposed.

InvalidOperationException

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 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.

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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