Begins an asynchronous read operation. (Consider using ReadAsync instead; see the Remarks section.)
Assembly: mscorlib (in mscorlib.dll)
[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)] public virtual IAsyncResult BeginRead( byte buffer, int offset, int count, AsyncCallback callback, Object 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.
In the .NET Framework 4 and earlier versions, you have to use methods such as and EndRead to implement asynchronous I/O 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 I/O operations more easily.
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.
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.