对象自动设置为Nothing Vb.Net

Question

我正在创建一个简单的服务器多客户端连接类。但是当我在VM上运行某些测试时，它会在某个时刻因错误而停止：

  

对象引用未设置为对象的实例。

我检查了调试，对象'b'设置为空。这是代码：
来自客户类的示例：

    Dim client As Client_Info,
        client_tcp As New TcpClient,
        client_stream As New MemoryStream,
        client_buffer As Byte() = {0}

    Dim msg_read_bytes_count As Integer,
        msg_header_size As Integer = 5,
        msg_header As Header_Info

    Dim header_bytes_count As Integer,
        data_bytes_count As Long

    Public Enum Enum_Data_Type
        TEXT = 1
        IMAGE = 2
        KEEP_ALIVE = 4
        FILE = 8
    End Enum
    Public Enum Enum_Connection_Status
        CONNECTED = 1
        DISCONNECTED = 2
    End Enum
    Public Structure Header_Info
        Dim PACK_SIZE As Integer
        Dim TYPE As Enum_Data_Type
    End Structure
    Public Structure Client_Info
        Dim Connection_Status As Enum_Connection_Status
        Dim ID As Integer
        Dim IP As String      ''The ID,Ip and port is used only by server for extra info.
        Dim Port As String
        Dim Computer_Name As String
        Dim Win_Ver As String
    End Structure

Sub New(ByVal hostname As String, ByVal port As Integer, ByVal client_info As Client_Info)
        Try

            With client
                .ID = client_info.ID
                .IP = client_info.IP
                .Computer_Name = client_info.Computer_Name
                .Win_Ver = client_info.Win_Ver
            End With

            client_tcp.BeginConnect(hostname, port, New AsyncCallback(AddressOf connect_to), client_tcp)

        Catch ex As Exception
            RaiseEvent Internal_Disconnected(ex)
        End Try

    End Sub
Public Sub Reconnect(ByVal hostname As String, ByVal port As Integer)
    Try
        If client.Connection_Status = Enum_Connection_Status.DISCONNECTED Then
            client_tcp = New TcpClient
            client_tcp.BeginConnect(hostname, port, New AsyncCallback(AddressOf connect_to), client_tcp)
        End If

    Catch ex As Exception
        RaiseEvent Internal_Disconnected(ex)
    End Try
End Sub
Public Sub SendText(ByVal text As String, Optional ByVal Data_TYPE As Enum_Data_Type = Enum_Data_Type.TEXT)
    Dim buffer As Byte() = ASCII.GetBytes(text)
    Dim header As Byte() = Create_Header(buffer.Length, Data_TYPE)

    Try

        If client.Connection_Status = 1 Then
            client_tcp.Client.Send(header)
            client_tcp.Client.Send(buffer)

            RaiseEvent Process_Info("Sent <" & buffer.Length & "> bytes of string <" & Data_TYPE & ">")
        End If
    Catch ex As Exception
        RaiseEvent Internal_Disconnected(ex)
    End Try
End Sub

客户的代码：

Imports System
Imports System.IO
Imports System.Net
Imports System.Threading
Imports System.Net.Sockets
Imports System.Text.Encoding
Imports TCP_Client.TCP_Client

Public Class Form1
    Dim info As Client_Info
    Dim b As TCP_Client.TCP_Client

    Delegate Sub add_conn_del()
    Delegate Sub proc_data(ByVal data As String)
    Delegate Sub disc_del(ByVal reason As Exception)


    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        With info
            .Computer_Name = "test_client"
            .ID = 1
            .IP = "10.000.11"
            .Win_Ver = "7"
        End With
        Dim b = New TCP_Client.TCP_Client("192.168.1.100", 60000, info)

        AddHandler b.Connected, AddressOf add_conn
        AddHandler b.Process_Info, AddressOf proccess
        AddHandler b.Disconnected, AddressOf disc
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        b.SendText(TextBox1.Text)  
        ''This is triggered when I want to send a message-->b is set here to 'nothing'
    End Sub


    Private Sub add_conn()
        If Label1.InvokeRequired Then
            Dim d As New add_conn_del(AddressOf add_conn)
            Me.Invoke(d)
        Else
            Label1.Text = "CONECTED!!!"
        End If
    End Sub
    Private Sub proccess(ByVal data As String)
        If Label1.InvokeRequired Then
            Dim d As New proc_data(AddressOf proccess)
            Me.Invoke(d, data)
        Else
            Label1.Text &= vbCrLf & data
        End If
    End Sub
    Private Sub disc(ByVal reason As Exception)
        If label1.InvokeRequired Then
            Dim d As New disc_del(AddressOf disc)
            Me.Invoke(d, reason)
        Else
            label1.Text &= vbCrLf & reason.Message
        End If
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        b.Reconnect("192.168.1.100", 60000)  ''this also doesn't work
    End Sub
End Class

这几乎是整个代码。其他地方没有错误。为什么'b'设置为空？