Imports System.Net         '網路基礎功能相關函數
Imports System.Net.Sockets '網路連線功能相關函數
Imports System.Text        '文字編碼功能相關函數
Imports System.Threading   '多執行緒功能相關函數
Public Class Form1
    '啟動監聽
    Dim U As UdpClient 'UDP監聽器
    Dim Th As Thread   '監聽執行緒
    '取得本機 IP (第一個合乎 IPv4規格的IP)
    Function localIP() As String
        Dim ip() As IPAddress = Dns.GetHostEntry(Dns.GetHostName).AddressList '取得本機IP陣列
        For Each it As IPAddress In ip '逐一檢視IP字串
            If it.AddressFamily = AddressFamily.InterNetwork Then '如果是IPv4型態的位址
                Return it.ToString '回傳IP字串
            End If
        Next
        Return "" '找不到合格IP
    End Function
    '關閉接聽執行續(如果有的話)
    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) _
        Handles Me.FormClosing
        Try
            U.Close() '關閉監聽器
            Th.Abort() '關閉監聽執行緒
        Catch ex As Exception
            '如果監聽執行緒沒開會出現錯誤，程式跳到此處執行，
            '此處不寫程式就是忽略錯誤，程式繼續執行的意思！
        End Try
    End Sub
End Class