FileStream.BeginWrite Method (Byte(), Int32, Int32, AsyncCallback, Object)
Begins an asynchronous write operation. (Consider using WriteAsync instead; see the Remarks section.)
Assembly: mscorlib (in mscorlib.dll)
<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> Public Overrides Function BeginWrite ( array As Byte(), offset As Integer, numBytes As Integer, userCallback As AsyncCallback, stateObject As Object ) As IAsyncResult
Parameters
- array
-
Type:
System.Byte()
The buffer containing data to write to the current stream.
- offset
-
Type:
System.Int32
The zero-based byte offset in array at which to begin copying bytes to the current stream.
- numBytes
-
Type:
System.Int32
The maximum number of bytes to write.
- userCallback
-
Type:
System.AsyncCallback
The method to be called when the asynchronous write operation is completed.
- stateObject
-
Type:
System.Object
A user-provided object that distinguishes this particular asynchronous write request from other requests.
| Exception | Condition |
|---|---|
| ArgumentException | array length minus offset is less than numBytes. |
| ArgumentNullException | array is null. |
| ArgumentOutOfRangeException | offset or numBytes is negative. |
| NotSupportedException | The stream does not support writing. |
| ObjectDisposedException | The stream is closed. |
| IOException | An I/O error occurred. |
In the .NET Framework 4 and earlier versions, you have to use methods such as BeginWrite and EndWrite to implement asynchronous file operations. These methods are still available in the .NET Framework 4.5 to support legacy code; however, the new async methods, such as ReadAsync, WriteAsync, CopyToAsync, and FlushAsync, help you implement asynchronous file operations more easily.
EndWrite must be called exactly once on every IAsyncResult from BeginWrite. EndWrite will block until the I/O operation has completed.
This method overrides BeginWrite.
FileStream provides two different modes of operation: synchronous I/O and asynchronous I/O. While either can be used, the underlying operating system resources might allow access in only one of these modes. By default, FileStream opens the operating system handle synchronously. In Windows, this slows down asynchronous methods. If asynchronous methods are used, use the FileStream(String, FileMode, FileAccess, FileShare, Int32, Boolean) constructor.
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 IO request, occur on the thread pool thread and become visible upon a call to EndWrite.
Multiple simultaneous asynchronous requests render the request completion order uncertain.
For a list of common file and directory operations, see Common I-O Tasks.
This code example is part of a larger example provided for the FileStream(String, FileMode, FileAccess, FileShare, Int32, Boolean) constructor.
Shared Sub Main() ' Create a synchronization object that gets ' signaled when verification is complete. Dim manualEvent As New ManualResetEvent(False) ' Create random data to write to the file. Dim writeArray(100000) As Byte Dim randomGenerator As New Random() randomGenerator.NextBytes(writeArray) Dim fStream As New FileStream("Test#@@#.dat", _ FileMode.Create, FileAccess.ReadWrite, _ FileShare.None, 4096, True) ' Check that the FileStream was opened asynchronously. If fStream.IsAsync = True Console.WriteLine("fStream was opened asynchronously.") Else Console.WriteLine("fStream was not opened asynchronously.") End If ' Asynchronously write to the file. Dim asyncResult As IAsyncResult = fStream.BeginWrite( _ writeArray, 0, writeArray.Length, _ AddressOf EndWriteCallback , _ New State(fStream, writeArray, manualEvent)) ' Concurrently do other work and then wait ' for the data to be written and verified. manualEvent.WaitOne(5000, False) End Sub
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0