我创建了这个类来跟踪互联网连接的变化。此类还可以检查稳定的互联网连接(稳定意味着在 N 秒内连接不会改变)。如果连接发生变化,该类会引发事件。
Imports System.IO
Imports System.Runtime.InteropServices
Imports System.Runtime.InteropServices.ComTypes
Imports System.Text
Imports System.Collections.Generic
Imports System.Linq
Imports System.Net.NetworkInformation
Imports System.Net
Public Enum InternetConnectionState
Connected
Disconnected
End Enum
Public Class NetworkConnections
Implements IDisposable
Public Shared Property CheckHostName As String = "www.google.com"
Public Property ConnectionStableAfterSec As Integer = 10
Private MonitoringStarted As Boolean = False
Private StableCheckTimer As System.Threading.Timer
Private IsFirstCheck As Boolean = True
Private wConnectionIsStable As Boolean
Private PrevInternetConnectionState As InternetConnectionState = InternetConnectionState.Disconnected
Public Event InternetConnectionStateChanged(ByVal ConnectionState As InternetConnectionState)
Public Event InternetConnectionStableChanged(ByVal IsStable As Boolean, ByVal ConnectionState As InternetConnectionState)
Public Sub StartMonitoring()
If MonitoringStarted = False Then
AddHandler NetworkChange.NetworkAddressChanged, AddressOf NetworkAddressChanged
MonitoringStarted = True
NetworkAddressChanged(Me, Nothing)
End If
End Sub
Public Sub StopMonitoring()
If MonitoringStarted = True Then
Try
RemoveHandler NetworkChange.NetworkAddressChanged, AddressOf NetworkAddressChanged
Catch ex As Exception
End Try
MonitoringStarted = False
End If
End Sub
Public ReadOnly Property ConnectionIsStableNow As Boolean
Get
Return wConnectionIsStable
End Get
End Property
<DllImport("wininet.dll")> _
Private Shared Function InternetGetConnectedState(ByRef Description As Integer, ByVal ReservedValue As Integer) As Boolean
End Function
Private Shared Function IsInternetAvailable() As Boolean
Try
Dim ConnDesc As Integer
Dim conn As Boolean = InternetGetConnectedState(ConnDesc, 0)
Return conn
Catch
Return False
End Try
End Function
Private Shared Function IsInternetAvailableByDns() As Boolean
Try
Dim iheObj As IPHostEntry = Dns.GetHostEntry(CheckHostName)
Return True
Catch
Return False
End Try
End Function
Public Shared Function CheckInternetConnectionIsAvailable() As Boolean
Return IsInternetAvailable() And IsInternetAvailableByDns()
End Function
Private Sub NetworkAddressChanged(sender As Object, e As EventArgs)
wConnectionIsStable = False
StableCheckTimer = New System.Threading.Timer(AddressOf ElapsedAndStable, Nothing, New TimeSpan(0, 0, ConnectionStableAfterSec), New TimeSpan(1, 0, 0))
If IsFirstCheck Then
If CheckInternetConnectionIsAvailable() Then
PrevInternetConnectionState = InternetConnectionState.Connected
RaiseEvent InternetConnectionStateChanged(InternetConnectionState.Connected)
Else
PrevInternetConnectionState = InternetConnectionState.Disconnected
RaiseEvent InternetConnectionStateChanged(InternetConnectionState.Disconnected)
End If
IsFirstCheck = False
Else
If CheckInternetConnectionIsAvailable() Then
If PrevInternetConnectionState <> InternetConnectionState.Connected Then
PrevInternetConnectionState = InternetConnectionState.Connected
RaiseEvent InternetConnectionStateChanged(InternetConnectionState.Connected)
End If
Else
If PrevInternetConnectionState <> InternetConnectionState.Disconnected Then
PrevInternetConnectionState = InternetConnectionState.Disconnected
RaiseEvent InternetConnectionStateChanged(InternetConnectionState.Disconnected)
End If
End If
End If
End Sub
Private Sub ElapsedAndStable()
If wConnectionIsStable = False Then
wConnectionIsStable = True
Dim hasnet As Boolean = CheckInternetConnectionIsAvailable()
RaiseEvent InternetConnectionStableChanged(True, IIf(hasnet, InternetConnectionState.Connected, InternetConnectionState.Disconnected))
End If
End Sub
#Region "IDisposable Support"
Private disposedValue As Boolean ' To detect redundant calls
' IDisposable
Protected Overridable Sub Dispose(disposing As Boolean)
If Not Me.disposedValue Then
If disposing Then
Try
RemoveHandler NetworkChange.NetworkAddressChanged, AddressOf NetworkAddressChanged
Catch ex As Exception
End Try
End If
' TODO: free unmanaged resources (unmanaged objects) and override Finalize() below.
' TODO: set large fields to null.
End If
Me.disposedValue = True
End Sub
' TODO: override Finalize() only if Dispose(ByVal disposing As Boolean) above has code to free unmanaged resources.
'Protected Overrides Sub Finalize()
' ' Do not change this code. Put cleanup code in Dispose(ByVal disposing As Boolean) above.
' Dispose(False)
' MyBase.Finalize()
'End Sub
' This code added by Visual Basic to correctly implement the disposable pattern.
Public Sub Dispose() Implements IDisposable.Dispose
' Do not change this code. Put cleanup code in Dispose(disposing As Boolean) above.
Dispose(True)
GC.SuppressFinalize(Me)
End Sub
#End Region
End Class
跟踪具有 2 个列表框的表单上的更改。重要的!这些事件是线程不安全的,需要使用调用方法进行处理。
Imports System.Net.NetworkInformation
Imports System.Net
Public Class frmNetworkConnections
Private WithEvents conn As NetworkConnections
Delegate Sub AddToList1Callback(ByVal ConnectionState As InternetConnectionState, ByVal IsStable As Boolean)
Delegate Sub AddToList2Callback(ByVal ConnectionState As InternetConnectionState, ByVal IsStable As Boolean)
Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
conn = New NetworkConnections
End Sub
Sub AddToList1(ByVal ConnectionState As InternetConnectionState, ByVal IsStable As Boolean)
If Me.InvokeRequired = True Then
Dim d As New AddToList1Callback(AddressOf AddToList1)
Me.Invoke(d, ConnectionState, IsStable)
Else
ListBox1.Items.Add(Now & " - State: " & ConnectionState.ToString() & ", Stable: " & IsStable)
End If
End Sub
Sub AddToList2(ByVal ConnectionState As InternetConnectionState, ByVal IsStable As Boolean)
If Me.InvokeRequired = True Then
Dim d As New AddToList2Callback(AddressOf AddToList2)
Me.Invoke(d, ConnectionState, IsStable)
Else
ListBox1.Items.Add(Now & " - State: " & ConnectionState.ToString() & ", Stable: " & IsStable)
ListBox2.Items.Add(Now & " - State: " & ConnectionState.ToString() & ", Stable: " & IsStable)
End If
End Sub
Private Sub conn_InternetConnectionStableChanged(IsStable As Boolean, ConnectionState As InternetConnectionState) Handles conn.InternetConnectionStableChanged
AddToList2(ConnectionState, IsStable)
End Sub
Private Sub conn_InternetConnectionStateChanged(ConnectionState As InternetConnectionState) Handles conn.InternetConnectionStateChanged
AddToList1(ConnectionState, False)
End Sub
Private Sub btnStartMonitoring_Click(sender As Object, e As EventArgs) Handles btnStartMonitoring.Click
btnStopMonitoring.Enabled = True
btnStartMonitoring.Enabled = False
conn.StartMonitoring()
End Sub
Private Sub btnStopMonitoring_Click(sender As Object, e As EventArgs) Handles btnStopMonitoring.Click
btnStopMonitoring.Enabled = False
btnStartMonitoring.Enabled = True
conn.StopMonitoring()
End Sub
End Class
结果是:
我使用稳定的连接更改。
如果不想跟踪更改,只检查连接,可以使用 CheckInternetConnectionIsAvailable() 共享函数。