System.IO.Stream.BeginWrite Method

Begins an asynchronous write operation. (Consider using Stream.WriteAsync(Byte[], int, int) instead; see the Remarks section.)

Syntax

public virtual IAsyncResult BeginWrite (byte[] buffer, int offset, int count, AsyncCallback callback, object state)

Parameters

buffer
The buffer to write data from.
offset
The byte offset in buffer from which to begin writing.
count
The maximum number of bytes to write.
callback
An optional asynchronous callback, to be called when the write is complete.
state
A user-provided object that distinguishes this particular asynchronous write request from other requests.

Returns

An IAsyncResult that represents the asynchronous write, which could still be pending.

Exceptions

TypeReason
NotSupportedExceptionThe current System.IO.Stream does not support writing.
System.IO.IOExceptionAn I/O error occurred.
ObjectDisposedExceptionThe stream is closed.

Remarks

In the .NET Framework 4 and earlier versions, you have to use methods such as Stream.BeginWrite(Byte[], int, int, AsyncCallback, object) and Stream.EndWrite(IAsyncResult) to implement asynchronous I/O operations. These methods are still available in the net_v45 to support legacy code; however, the new async methods, such as Stream.ReadAsync(Byte[], int, int), Stream.WriteAsync(Byte[], int, int), Stream.CopyToAsync(Stream), and Stream.FlushAsync, help you implement asynchronous I/O operations more easily.

The default implementation of BeginWrite on a stream calls the Stream.Write(Byte[], int, int) method synchronously, which means that Write might block on some streams. However, instances of classes such as FileStream and NetworkStream fully support asynchronous operations if the instances have been opened asynchronously. Therefore, calls to BeginWrite will not block on those streams. You can override BeginWrite (by using async delegates, for example) to provide asynchronous behavior.

Pass the IAsyncResult returned by the current method to Stream.EndWrite(IAsyncResult) to ensure that the write completes and frees resources appropriately. Stream.EndWrite(IAsyncResult) must be called once for every call to Stream.BeginWrite(Byte[], int, int, AsyncCallback, object). You can do this either by using the same code that called BeginWrite or in a callback passed to BeginWrite. If an error occurs during an asynchronous write, an exception will not be thrown until EndWrite is called with the IAsyncResult returned by this method.

If a stream is writable, writing at the end of the stream expands the stream.

The current position in the stream is updated when you issue the asynchronous read or write, not when the I/O operation completes. Multiple simultaneous asynchronous requests render the request completion order uncertain.

Use the Stream.CanWrite property to determine whether the current instance supports writing.

If a stream is closed or you pass an invalid argument, exceptions are thrown immediately from BeginWrite. Errors that occur during an asynchronous write request, such as a disk failure during the I/O request, occur on the thread pool thread and throw exceptions when calling EndWrite.

Requirements

Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0, 2.0.0.0, 4.0.0.0