Begins an asynchronous read operation.
Assembly: mscorlib (in mscorlib.dll)
'Declaration <HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> _ Public Overridable Function BeginRead ( _ buffer As Byte(), _ offset As Integer, _ count As Integer, _ callback As AsyncCallback, _ state As Object _ ) As IAsyncResult 'Usage Dim instance As Stream Dim buffer As Byte() Dim offset As Integer Dim count As Integer Dim callback As AsyncCallback Dim state As Object Dim returnValue As IAsyncResult returnValue = instance.BeginRead(buffer, _ offset, count, callback, state)
- Type: System.Byte()
The buffer to read the data into.
- Type: System.Int32
The byte offset in buffer at which to begin writing data read from the stream.
- Type: System.Int32
The maximum number of bytes to read.
- Type: System.AsyncCallback
An optional asynchronous callback, to be called when the read is complete.
- Type: System.Object
A user-provided object that distinguishes this particular asynchronous read request from other requests.
Attempted an asynchronous read past the end of the stream, or a disk error occurs.
One or more of the arguments is invalid.
Methods were called after the stream was closed.
The current Stream implementation does not support the read operation.
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.
For an example of creating a file and writing text to a file, see How to: Write Text to a File. For an example of reading text from a file, see How to: Read Text from a File. For an example of reading from and writing to a binary file, see How to: Read and Write to a Newly Created Data File. For an example of asynchronous file I/O, see Asynchronous File I/O.
The default implementation of BeginRead on a stream calls the Read method synchronously, which means that Read 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 BeginRead will not block on those streams. You can override BeginRead (by using async delegates, for example) to provide asynchronous behavior.
Pass the IAsyncResult return value to the EndRead method of the stream to determine how many bytes were read and to release operating system resources used for reading. EndRead must be called once for every call to . You can do this either by using the same code that called BeginRead or in a callback passed to BeginRead.
The current position in the stream is updated when the asynchronous read or write is issued, not when the I/O operation completes.
Multiple simultaneous asynchronous requests render the request completion order uncertain.
Use the CanRead property to determine whether the current instance supports reading.
If a stream is closed or you pass an invalid argument, exceptions are thrown immediately from BeginRead. Errors that occur during an asynchronous read request, such as a disk failure during the I/O request, occur on the thread pool thread and throw exceptions when calling EndRead.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.