• Articolo

Stream.BeginWrite Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Begins an asynchronous write operation.

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

Syntax

'Declaration
Public Overridable Function BeginWrite ( _
    buffer As Byte(), _
    offset As Integer, _
    count As Integer, _
    callback As AsyncCallback, _
    state As Object _
) As IAsyncResult

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

Parameters

  • buffer
    Type: array<System.Byte[]
    The buffer to write data from.
  • offset
    Type: System.Int32
    The byte offset in buffer from which to begin writing.
  • count
    Type: System.Int32
    The maximum number of bytes to write.
  • callback
    Type: System.AsyncCallback
    An optional asynchronous callback, to be called when the write is complete.
  • state
    Type: System.Object
    A user-provided object that distinguishes this particular asynchronous write request from other requests.

Return Value

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

Exceptions

Exception Condition
IOException

Attempted an asynchronous write past the end of the stream, or a disk error occurs.
ArgumentException

One or more of the arguments is invalid.
ObjectDisposedException

Methods were called after the stream was closed.
NotSupportedException

The current Stream implementation does not support the write operation.

Remarks

The default implementation of BeginWrite on a stream calls the Write method synchronously, which means that Write might block on some streams. However, instances of classes such as FileStream 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 EndWrite to ensure that the write completes and frees resources appropriately. EndWrite must be called once for every call to BeginWrite. 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 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.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.