Begin Read(Byte, Int32, Int32, AsyncCallback, Object) Method
Begins an asynchronous read operation. (Consider using ReadAsync(Byte, Int32, Int32) instead.)
public: virtual IAsyncResult ^ BeginRead(cli::array <System::Byte> ^ buffer, int offset, int count, AsyncCallback ^ callback, System::Object ^ state);
public virtual IAsyncResult BeginRead (byte buffer, int offset, int count, AsyncCallback callback, object state);
abstract member BeginRead : byte * int * int * AsyncCallback * obj -> IAsyncResult override this.BeginRead : byte * int * int * AsyncCallback * obj -> IAsyncResult
Public Overridable Function BeginRead (buffer As Byte(), offset As Integer, count As Integer, callback As AsyncCallback, state As Object) As IAsyncResult
The buffer to read the data into.
The byte offset in
buffer at which to begin writing data read from the stream.
The maximum number of bytes to read.
An optional asynchronous callback, to be called when the read is complete.
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.
Stream implementation does not support the read operation.
In the .NET Framework 4 and earlier versions, you have to use methods such as BeginRead 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
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.
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 BeginRead. You can do this either by using the same code that called
BeginRead or in a callback passed to
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