[RESOLVED] Don't quite understand this warning; Access of shared member....

Hi,

I have a class called InternetDetector that is checking to see if internet is available, and if available, add a Label to a form.

I declare the class like this:

vb.net Code:

Dim id As InternetDetector = New InternetDetector(2500, My.Settings.CheckInternetHostName, Me, _uiLanguage)
id.Start()

That will give me a warning, saying that Access of shared member, constant member, enum member or nested type through an instance; qualifing expression will not be evaluated, and it suggest me to change my code to:

vb.net Code:

Dim id As InternetDetector = New InternetDetector(2500, My.Settings.CheckInternetHostName, Me, _uiLanguage)
InternetDetector.Start()

Both of them work, but how is it that InternetDetector.Start knows the parameters of id? :)

InternetDetector class:

vb.net Code:

Option Strict On
Option Explicit On
 
Imports System.Drawing
Imports System.Windows.Forms
 
Public Class InternetDetector
    Private Shared _host As String = Nothing
    Private Shared _interval As Integer = 1000
    Private Shared _form As Object = Nothing
    Private Shared _uiLanguage As String = Nothing
 
    Public Sub New(ByVal interval As Integer, ByVal host As String, ByVal sender As Object, ByVal uiLanguage As String)
        _host = host
        _interval = interval
        _form = sender
        _uiLanguage = uiLanguage
    End Sub
 
    Public Shared WithEvents checkTimer As New System.Timers.Timer(_interval)
 
    Public Shared Sub Start()
        checkTimer.Start()
 
    End Sub
 
    Public Shared Sub [Stop]()
        checkTimer.Stop()
 
    End Sub
 
    Public Shared Sub m_Timer_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles checkTimer.Elapsed
 
        InternetDetector_Result(IsInternetIsAvailable(_host))
 
    End Sub
 
    Private Delegate Sub InternetDetector_ResultCallback(ByVal result As Boolean)
    Private Shared Sub InternetDetector_Result(ByVal result As Boolean)
        Dim f As Form = DirectCast(_form, Form)
 
        If f.InvokeRequired Then
            f.Invoke(New InternetDetector_ResultCallback(AddressOf InternetDetector_Result), result)
 
 
        Else
            'Some crazy code to add a label to a form
 
        End If
    End Sub
 
    Private Shared Function IsInternetIsAvailable(ByVal host As String) As Boolean
        Try
            Dim a As System.Net.IPHostEntry = System.Net.Dns.GetHostEntry(host)
            Return True
 
        Catch ex As System.Net.Sockets.SocketException
            Return False
 
        End Try
 
    End Function
 
End Class

That's because everything in your class is shared which in fact makes it a module rather than a class. If you would create a second object you would also change the first since nothing in your class belongs to the object instance.

Ahh, thank you Joachim. I will go over the code later tonight, need to go out now and bbq before it starts to rain :)

Why do you think that it is necessary to check if the internet is available? A better question is what is internet availability? It looks like you have defined it to mean that a hostname can be resolved, regardless of who provides the response.

Some of the features in the application is depending on internet, and they will get disabled if the host can not be reached. The label I am adding through that class is just to show the user if internet is available or not.

Attachment 99973

If this is not what you meant, please let me know :)

Quote:

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Originally Posted by _powerade_

... if internet is available or not.

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What do you mean by the above statement? Your code checks to see if a name can be resolved. What if it is resolved by the DNS Resolver running on the local PC?

You are also assuming that nothing happens between the time you check if the internet is available and using it. What if it is not up when you check, and the next instant it comes back up? What if you check and it is up, and the next instant it goes down?

It has been my experience that these kinds of checks do not accomplish anything when examined closely.

I have very little experience on this topic, so I guess everything you write here is correct. So what do you suggest me to do? Would it be better if I use the IP-address instead, or just simply go for a Ping? From what I have read on MSDN, using the Ping method isn't that reliable either...

I plan to check within a 5 to 10 second interval, and if it gets unavailable between the checks, then I must handle that in code.

But nonetheless, I think it's a nice gimmick to show it in the statusbar :p

Quote:

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Originally Posted by _powerade_

I have very little experience on this topic, so I guess everything you write here is correct. So what do you suggest me to do? Would it be better if I use the IP-address instead, or just simply go for a Ping? From what I have read on MSDN, using the Ping method isn't that reliable either...

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I'd suggest not bothering with it at all. Whatever your code is really doing has to be wrapped in a Try-Catch right?

Quote:

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Originally Posted by _powerade_

...But nonetheless, I think it's a nice gimmick to show it in the statusbar :p

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Gimmick is correct.