[Visual Basic] TCP Port scanner by Frekvens1

'CODE WRITTEN BY FREKVENS1, www.Frekvens1.webs.com.
'THIS CODE WAS WRITTEN FOR 'DSW Tutorials' AS ANOTHER WAY TO DO THE SAME TASK BETTER. CREDITS TO HIM/HER/THEM FOR MAKING THE VIDEO!
'https://www.youtube.com/watch?v=5qpn0vxKr6c'
'Feel free to use the code at own will, and if you need help understanding it better give me a call!
'This is not the optimal code, but instead used to learn more.
'Thanks for watching my code, and I hope you find something useful in here! (VB.NET).
Imports System.Threading
Imports System.Net.Sockets

Public Class Form1
    WithEvents checkPort As ScanPort
    Private newPort As String, Working As Boolean

    Private Sub btnScan_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnScan.Click
        If Working Then
            MsgBox("[ERROR] Scan is still running!", MsgBoxStyle.Critical)
        Else
            Try
                lbPorts.Items.Clear() 'Clears the listbox for a new scan.
                Working = True
                Dim t As New Thread(AddressOf startScan) 'Lag preventer.
                t.Start()
            Catch ex As Exception
                Working = False
            End Try
        End If

    End Sub

    Private Sub startScan() 'Just to make the UI (User Interface (Main Thread) ) less 'laggy'.
        checkPorts(txtIP.Text, nudStart.Value, nudStop.Value) 'Starts the port scanner, checking each of the desired ports.
    End Sub

    Private Sub checkPorts(ByVal IPaddress As String, ByVal PortRangeStart As Integer, ByVal PortRangeMax As Integer)
        Working = True

        Try
            For Port = PortRangeStart To PortRangeMax 'Increases the port value by 1 until it reaches the max value, starting from the start value.
                Thread.Sleep(20) 'Not needed, but keeps the software from freezing.
                checkPort = New ScanPort(IPaddress, Port) 'Creates a new instance of the ScanPort class, starting the desired port scan.
            Next
        Catch ex As Exception
            Working = False
        End Try

        Working = False
    End Sub

    Private Sub ScanPort_Result(ByVal Port As String, ByVal Success As Boolean) Handles checkPort.Result
        If Success Then 'If the connection was successful, then it will be added to be seen.
            newPort = Port 'Sets the local value newPort to the current port.
            addItem() 'Adds the item to the listbox.
        End If
    End Sub

    Private Sub addItem()
        If Me.lbPorts.InvokeRequired Then 'If this sub is runned in another thread, invoke the UI thread to edit it's objects.
            Me.lbPorts.Invoke(New MethodInvoker(AddressOf addItem)) 'Code not being runned by the main thread, therefore is invoking the object to edit it.
        Else
            Me.lbPorts.Items.Add("Open port: " & newPort) 'Adds the open port to the listbox.
        End If
    End Sub
End Class

Public Class ScanPort 'A class for to scan ports
    Public Shared Event Result(ByVal Port As String, ByVal Success As Boolean)
    Private IP As String, Port As Integer

    Sub New(ByVal IP As String, ByVal Port As Integer)
        Me.IP = IP 'Sets the local value 'IP' of the class to the new desired IP.
        Me.Port = Port 'Sets the local value 'Port' of the class to the new desired Port.

        Dim tmpThread As New Thread(AddressOf checkPort) 'Creates a new temporary thread to run the port scan on.
        tmpThread.Start() 'Starts the new thread.
    End Sub

    Sub checkPort()
        Dim tmpClient As New TcpClient() 'Creates a new instance of the temporary TCPclient.
        Try
            tmpClient.Connect(IP, Port) 'Connects to the selected port by the desired IP.
            Thread.Sleep(50) 'This is the value in miliseconds the TCPclient have to connect, before timing out.
            RaiseEvent Result(Port, tmpClient.Connected) 'Raising the event 'Result' with the desired answer, wheter it succeeded or failed.
            tmpClient.Close()
        Catch ex As Exception
            tmpClient.Close()
            RaiseEvent Result(Port, False) 'Some error happened while trying to connect, return the value of false.
        End Try
    End Sub
End Class