Visual Basic.net 檢測網絡連接狀態的兩種方法

一.簡單實現檢測網絡連接狀態

Public Class Form1
    '獲取網絡連接狀態
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If My.Computer.Network.IsAvailable = True Then
            Me.TextBox1.Text = "計算機已連接到網絡上"
        Else
            Me.TextBox1.Text = "計算機未連接到網絡上"
        End If
    End Sub
End Class

二.用wininet.dll判斷網絡是否正常連接的方法
作者沒有采用.Net自己提供的My.Computer.Network.IsAvailable去判斷網絡是否正常連接，而是調用了Wininet.dll來判斷。
代碼如下：

Imports System
Imports System.Runtime.InteropServices
Imports System.Text

''' <summary>
''' Determine whether or not there is a connection to the Internet present on the local machine.
''' </summary>
''' <remarks></remarks>
Public Class InternetConnectionCheck

    <DllImport("WININET", CharSet:=CharSet.Auto)> _
    Private Shared Function InternetGetConnectedState(ByRef lpdwFlags As InternetConnectionState, ByVal dwReserved As Integer) As Boolean
    End Function

    <Flags()> _
    Public Enum InternetConnectionState As Integer
        INTERNET_CONNECTION_MODEM = &H1
        INTERNET_CONNECTION_LAN = &H2
        INTERNET_CONNECTION_PROXY = &H4
        INTERNET_RAS_INSTALLED = &H10
        INTERNET_CONNECTION_OFFLINE = &H20
        INTERNET_CONNECTION_CONFIGURED = &H40
    End Enum

    ''' <summary>
    ''' Call this function to know whether the internet is connected or not.
    ''' </summary>
    ''' <returns>Boolean</returns>
    ''' <remarks></remarks>
    Public Shared Function IsInternetConnected() As Boolean
        Dim flags As InternetConnectionState = 0
        Try
            If InternetGetConnectedState(flags, 0) Then
                Return True
            Else
                Return False
            End If
        Catch ex As Exception
            Throw ex
        Finally
            flags = Nothing
        End Try
    End Function

End Class