July 25, 2008 11:07am pdt

02.19.2008 at 05:53AM PST, ID: 23174286

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7.2

Events and global variables

Zones: .NET, Miscellaneous Programming, Microsoft Visual Basic.Net

Tags: VB, C#, MS WebBrowser object

I'm working on a VB.NET screen scraping application that hosts a WebBrowser control. I have a global variable that needs to be available to each step of the application and then changed before running a new sequence of web activities. An example follows.
It works as expected when Step1 is only called once. This is output by debug.print when RunnAll is called:
end Step1-1
end Step2-1

A curious (to me) thing happens when I attempt to run the Step1-Step2 sequence multiple times. If I uncomment lines 9-12 and run I get the following debug.print output:
end Step1-1
end Step1-2
end Step1-3
end Step2-3
end Step2-3
end Step2-3
It looks as if Step1 is being called three times as expected but the DocumentCompleted event is only being triggered or handled for the last call to Step1. I would sure appreciate it if someone could explain what is happening here. It's probably something obvious but I can't see it. Thanks.

         
           
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             Module Module1
    Dim b As WebBrowser = Form1.WebBrowser1
    Dim doc As HtmlDocument = b.Document
    Dim number As Integer = 0 'global variable to be available in all steps
 
    Public Sub RunAll()
        number = 1
        Step1(number)
        'number = 2
        'Step1(number)
        'number = 3
        'Step1(number)
    End Sub
 
    Public Sub Step1(ByVal i As Integer)
        AddHandler b.DocumentCompleted, AddressOf Step2
        number = i
        b.Navigate("cnn.com")
        Debug.Print("end Step1-" & number)
    End Sub
 
    Public Sub Step2(ByVal sender As System.Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs)
        RemoveHandler b.DocumentCompleted, AddressOf Step2
        b.Navigate("google.com")
        Debug.Print("end Step2-" & number)
    End Sub
End Module

           
         

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Question Stats

Zone: Programming

Question Asked By: thefridgeVFA

Solution Provided By: gbzhhu

Participating Experts: 2

Solution Grade: B

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