我已经做了大量的搜索,并且我确定我很接近,但是我遇到了问题并希望有人能够提供帮助。阅读异步网络流
我有一个以太网条码扫描器,我需要不断地收听。我试过使用NetworkStream
。在单独的线程中阅读,但后来发现异步网络流有'BeginRead
'功能。问题是我无法得到它的工作。
下面是我得到了代码:
Public Class ScannerConnect
Private client As TcpClient
Property server As String
Property port As Int32 = 2005
Private data As [Byte]()
Sub Connect()
Try
client = New TcpClient(server, port)
Catch e As ArgumentNullException
Console.WriteLine("ArgumentNullException: {0}", e)
Catch e As SocketException
Console.WriteLine("SocketException: {0}", e)
End Try
End Sub 'Connect
Sub ListenASync()
stream = client.GetStream()
data = New [Byte](256) {}
stream.BeginRead(data, 0, data.Length, AddressOf ReadASync, stream)
End Sub
Private Sub ReadASync(ar As IAsyncResult)
Dim buffer As Byte() = TryCast(ar.AsyncState, Byte())
Dim bytesRead As Integer = stream.EndRead(ar)
Dim message As String = Encoding.ASCII.GetString(buffer, 0, bytesRead)
MsgBox(message)
stream.BeginRead(buffer, 0, buffer.Length, AddressOf ReadASync, buffer)
End Sub
End Class
它崩溃上 昏暗的消息String = Encoding.ASCII.GetString(buffer, 0, bytesRead)
错误 Array
不能null
。
任何想法我做错了什么?
如果TryCast失败,不会'Byte'为空/空,因为你不检查它,你会得到错误 – Plutonix