Question

我做了相当多的搜索，我确信我很接近，但我遇到了问题并希望有人可以提供帮助。

我有一个以太网条形码扫描仪，我需要不断收听。我尝试过使用NetworkStream。在另一个线程中读取，但后来发现异步网络流有一个“BeginRead”函数。问题是我根本无法使用它。

这是我得到的代码：

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

它崩溃了昏暗消息为String = Encoding.ASCII.GetString(buffer, 0, bytesRead) 有错误 Array不能是null。

任何想法我做错了什么？

Answer 1

您将stream（NetworkStream）作为AsyncState参数传递给BeginRead()。
您无法将其转换为Byte()回调中的EndRead。

读取ASync网络流

1 个答案: