Vb.net 读取异步网络流
我已经做了大量的搜索,我相信我很接近,但我有问题,希望有人能帮助我 我有一个以太网条形码扫描仪,我需要经常听。我尝试过使用Vb.net 读取异步网络流,vb.net,networking,networkstream,Vb.net,Networking,Networkstream,我已经做了大量的搜索,我相信我很接近,但我有问题,希望有人能帮助我 我有一个以太网条形码扫描仪,我需要经常听。我尝试过使用NetworkStream。在单独的线程中阅读,但后来发现异步网络流有一个“BeginRead”函数。问题是我根本无法让它工作 以下是我得到的代码: Public Class ScannerConnect Private client As TcpClient Property server As String Property port As Int
NetworkStream
。在单独的线程中阅读,但后来发现异步网络流有一个“BeginRead
”函数。问题是我根本无法让它工作
以下是我得到的代码:
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
它撞坏了
将消息变暗为String=Encoding.ASCII.GetString(缓冲区,0,字节读取)
错误地
Array
不能为null
知道我做错了什么吗?您将
流
(a网络流
)作为AsyncState参数传递给BeginRead()
您不能在
EndRead
回调中将其转换为Byte()
。如果TryCast失败,那么Byte
将不会为null/空,并且由于您没有检查它,因此将来会出现错误,请使用调试器找出null。