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System Internet Connection - Determining How and If Connected

Author:

Steve McMahon(steve@vbaccelerator.com)

Keywords:

API,Internet,Windows

Updated:

17/08/99

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If you are designing a project which can use an Internet connection, it can be useful to know whether the system is connected or not. There are various methods of doing this, however the most informative and reliable method is to use the WinInet.DLL InternetGetConnectedStateEx() API call. The only problem with this call is it is only implemented for the WinInet.DLL version shipped with Internet Explorer version 4.0 or higher.

To test out this function, start a new project and add the following code:



Public Declare Function InternetGetConnectedStateEx Lib "wininet.dll" Alias "InternetGetConnectedStateExA" _
(ByRef lpdwFlags As Long, _
ByVal lpszConnectionName As String, _
ByVal dwNameLen As Long, _
ByVal dwReserved As Long _
) As Long

Public Enum EIGCInternetConnectionState
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

Public Property Get InternetConnected( _
Optional ByRef eConnectionInfo As EIGCInternetConnectionState, _
Optional ByRef sConnectionName As String _
) As Boolean
Dim dwFlags As Long
Dim sNameBuf As String
Dim lR As Long
Dim iPos As Long
sNameBuf = String$(513, 0)
lR = InternetGetConnectedStateEx(dwFlags, sNameBuf, 512, 0&)
eConnectionInfo = dwFlags
iPos = InStr(sNameBuf, vbNullChar)
If iPos > 0 Then
sConnectionName = Left$(sNameBuf, iPos - 1)
ElseIf Not sNameBuf = String$(513, 0) Then
sConnectionName = sNameBuf
End If
InternetConnected = (lR = 1)
End Property

To try out the code, add a CommandButton and a Multi-Line TextBox to your test project's main form. Then add the following code to try the function:


Private Sub Command1_Click()
Dim eR As EIGCInternetConnectionState
Dim sMsg As String
Dim sName As String
Dim bConnected As Boolean

' Determine whether we have a connection:
bConnected = InternetConnected(eR, sName)

' The connection state info parameter provides details
' about how we connect:
If (eR And INTERNET_CONNECTION_MODEM) = INTERNET_CONNECTION_MODEM Then
sMsg = sMsg & "Connection uses a modem." & vbCrLf
End If
If (eR And INTERNET_CONNECTION_LAN) = INTERNET_CONNECTION_LAN Then
sMsg = sMsg & "Connection uses LAN." & vbCrLf
End If
If (eR And INTERNET_CONNECTION_PROXY) = INTERNET_CONNECTION_PROXY Then
sMsg = sMsg & "Connection is via Proxy." & vbCrLf
End If
If (eR And INTERNET_CONNECTION_OFFLINE) = INTERNET_CONNECTION_OFFLINE Then
sMsg = sMsg & "Connection is Off-line." & vbCrLf
End If
If (eR And INTERNET_CONNECTION_CONFIGURED) = INTERNET_CONNECTION_CONFIGURED Then
sMsg = sMsg & "Connection is Configured." & vbCrLf
Else
sMsg = sMsg & "Connection is Not Configured." & vbCrLf
End If
If (eR And INTERNET_RAS_INSTALLED) = INTERNET_RAS_INSTALLED Then
sMsg = sMsg & "System has RAS installed." & vbCrLf
End If

' Display the connection name and info:
If bConnected Then
Text1.Text = "Connected: " & sName & vbCrLf & vbCrLf & sMsg
Else
Text1.Text = "Not Connected: " & sName & vbCrLf & vbCrLf & sMsg
End If

End Sub

Run the project. When you click the command button, the text box will be updated with the status of the current connection, the name of RAS dial-up connection used (if applicable) and also various information about how the connection is being achieved (i.e. by modem or LAN, via a proxy and whether the connection is configured or not).


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Copyright 1998-1999, Steve McMahon ( steve@vbaccelerator.com). All Rights Reserved.
Last updated: 17/08/99