Visual Basic System.invalidOperationexception

Question

所以我得到这个错误，说我得到了一个System.invalidOperationexception 这是完整的错误：

[Managed to Native Transition]
Port Scan.exe!WindowsApplication1.My.MyProject.MyForms.Form1.get()
Port Scan.exe!WindowsApplication1.My.MyApplication.OnCreateMainForm()
    Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicatio Base.OnRun()
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplication    Base.DoApplicationModel()
Microsoft.VisualBasic.dll!Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplication    Base.Run(string[] commandLine)
[Native to Managed Transition]
mscorlib.dll!System.Runtime.Hosting.ApplicationActivator.CreateInstance(System.ActivationCo    ntext activationContext, string[] activationCustomData)
    Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.H    ostProc.RunUsersAssemblyDebugInZone()
    mscorlib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContex   t executionContext, System.Threading.ContextCallback callback, object state, bool      preserveSyncCtx)
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext   executionContext, System.Threading.ContextCallback callback, object state, bool  preserveSyncCtx)
 mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext     executionContext, System.Threading.ContextCallback callback, object state)
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart()
[Native to Managed Transition]

这是我正在尝试编译的代码，它用于端口扫描程序

Public Class Form1
Dim host As String

Dim counter As Integer
Dim portmin As Integer = TextBox3.Text
Dim portmax As Integer = TextBox2.Text
Private Sub Form1_Load(ByVal sender As System.Object, _
            ByVal e As System.EventArgs) Handles MyBase.Load
    Button1.Enabled = False
    'set counter explained before to 0
    counter = 0
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Timer1.Tick
    'Set the host and port and counter
    counter = counter + 1 'counter is for the timer
    host = TextBox1.Text



    For port As Integer = portmin To portmax

        If (port = portmax) Then
            Exit For
        End If



        ' Next part creates a socket to try and connect 
        ' on with the given user information.

        Dim hostadd As System.Net.IPAddress = _
            System.Net.Dns.GetHostEntry(host).AddressList(0)
        Dim EPhost As New System.Net.IPEndPoint(hostadd, port)
        Dim s As New System.Net.Sockets.Socket( _
      System.Net.Sockets.AddressFamily.InterNetwork, _
    System.Net.Sockets.SocketType.Stream, _
      System.Net.Sockets.ProtocolType.Tcp)
        Try
            s.Connect(EPhost)
        Catch
        End Try
        If Not s.Connected Then
            ListBox1.Items.Add("Port " + port.ToString + " is not open")
        Else
            ListBox1.Items.Add("Port " + port.ToString + " is open")
            ListBox2.Items.Add(port.ToString)

        End If
        Label3.Text = "Open Ports: " + ListBox2.Items.Count.ToString
    Next
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, _
            ByVal e As System.EventArgs) Handles Button1.Click
    'stop button
    Timer1.Stop()
    Timer1.Enabled = False
    Button1.Enabled = True
    Button2.Enabled = False
End Sub

Private Sub Button2_Click(ByVal sender As System.Object, _
  ByVal e As System.EventArgs) Handles Button2.Click
    ListBox1.Items.Add("Scanning: " + TextBox1.Text)
    ListBox1.Items.Add("-------------------")
    Button2.Enabled = True
    Button1.Enabled = False
    Timer1.Enabled = True
    Timer1.Start()
End Sub

Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged

End Sub

Private Sub TextBox2_TextChanged(sender As Object, e As EventArgs) Handles TextBox2.TextChanged

End Sub

Private Sub ListBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox2.SelectedIndexChanged

End Sub
End Class

我真的很感谢你的帮助，因为我一直坚持这个错误并且无法构建exe。似乎错误只发生在我执行for循环以允许最小和最大端口号时。

Answer 1

问题在于此代码：

Dim portmin As Integer = TextBox3.Text
Dim portmax As Integer = TextBox2.Text

在执行这些陈述时，表格尚未完全构建。尚未创建TextBox2和TextBox3。您正尝试将引用Nothing分配给整数值。这是不允许的。将分配移动到表单的Load事件。还要花时间检查并确保这些框的内容转换为整数。