Check Connection - Website (VB.Net)

[Jack21]

Hi .... can anyone help?

I have a piece of code that checks to see if a connection exists but am experiencing some issues as the website is recognised as "Not Authorised" (specifically a 401 error). Please note the code works perfectly for http://www.amazon.com" onclick="window.open(this.href);return false; etc. I know the website exists if I get the error but I am struggling to know how to trap the error as I am unable to do this within a Try/Catch (I have to admit the code has been supplied by a very kind indivdiual who posted it on the internet). The code is below:

Dim url As New System.Uri("http://learningguide/")
Dim req As System.Net.WebRequest
req = System.Net.WebRequest.Create(url)
Dim resp As System.Net.WebResponse

Try
resp = req.GetResponse()
resp.Close()
req = Nothing
MsgBox("Website Found!")
IsConnectionAvailable = True
Catch ex As Exception
req = Nothing
MsgBox("Website not found. Check the url and internet connection")
IsConnectionAvailable = False
End Try

If someone can indicate where I can place the error trap I would be very grateful. I am aware that once "resp = req.GetResponse" runs, the 401 error appears then the code jumps to "Catch ex as Exception".

Thanks in advance
Jack

[HansV]

I'm not familiar with VB.Net so I can't help with the technical side, but shouldn't the URL be http://learningguide.com" onclick="window.open(this.href);return false; or http://learningguide.co.uk" onclick="window.open(this.href);return false; or something like that?

[Jack21]

Hi Hans

I've looked into this further and am now aware that I can trap the Exception (Catch ex as Exception), so I'll take a look and see if I can resolve the issue.

Thanks as always
Jack

[agibsonsw]

Hello. From my vast knowledge of VB.Net (he, he), Exception catches all Exceptions, but the error you receive might be something other than a website not being found, perhaps some security warning/message.

So you need to find out, easiest by debugging/stepping through the code, the specific Exception Class and Type that occurs for the site. Then you can catch this specific Exception - before the catch all Exception.

Code: Select all

Catch ex As SomeExceptionClass.SpecificException
    'need to first find out the particular Exception that occurred
    IsConnectionAvailable = True    'possibly..
Catch ex As Exception
    req = Nothing
    MsgBox(ex.Message)
    Stop    'enter debugging mode so you can determine the Exception Class and Type
    IsConnectionAvailable = False
End Try

Exceptions have a Message property that you can display, but it's really the Exception Class/Type that you need to discover. When you are debugging within the Catch clause I believe that you can just hover the mouse over 'ex' to discover this information.

Hope I've been of some (little) help. Andy.

[agibsonsw]

Hello. The particular Exception raised has a Response and a Status property. The Response doesn't seem useful.

Code: Select all

  Dim IsConnectionAvailable As Boolean = False

        Dim url As New System.Uri("http://learningguide/")
        Dim req As System.Net.WebRequest
        req = System.Net.WebRequest.Create(url)
        Dim resp As System.Net.WebResponse

        Try
            resp = req.GetResponse()
            resp.Close()
            req = Nothing
            MsgBox("Website Found!")
            IsConnectionAvailable = True
        Catch ex As System.Net.WebException
            If ex.Status.ToString.Contains("NameResolutionFailure") Then
                MsgBox("Please check that the web address is correctly typed.")
                IsConnectionAvailable = False
            End If
        Catch ex As Exception
            MsgBox("Website not found. Check the url and internet connection")
            IsConnectionAvailable = False
        Finally
            req = Nothing   'not normally necessary in VB.Net
        End Try
    End Sub

You could move 'req = Nothing' into the Finally clause so that it will ALWAYS be called, but in .Net it's generally not essential (because of Garbage Collection).

Andy.

[Jack21]

Thanks for your help Andy .... all sorted and running like a dream.