Question

I have spent way too much time trying to sort this little issue out. I have narrowed down the issue to the exact procedure that throws the error. Yes, I have used Google.. Just throwing that out there before some wise guy replies “search google”!

Anyways, here:

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Try
    Dim tempSource as String = Nothing
    Console.WriteLine("Loading document...")

    Dim FILE_NAME As String = "C:\pathto\file.txt"
    If System.IO.File.Exists(FILE_NAME) = True Then
        Dim objReader As New System.IO.StreamReader(FILE_NAME)
        tempSource = objReader.ReadToEnd
        objReader.Close()
        Console.WriteLine("Loaded the document!")
    Else
        Console.WriteLine("Error loading document!")
        MsgBox("Error loading document!")
        Exit Sub
    End If

    Dim doc As HtmlDocument = Nothing
    If tempSource IsNot Nothing Then
        Console.WriteLine("Temp Source was not nothing, so loading HAP doc")
        doc.Load(tempSource)  '<--- This is where the error is!!!!!
        Console.WriteLine("HAP doc loaded!")
    Else
        Console.WriteLine("Error: Unable to load source file into parser!")
        MsgBox("Error: Unable to load source file into parser!")
        Exit Sub
    End If
    Console.WriteLine("Document loaded!")
    Console.WriteLine("Processing...")

    For Each node As HtmlNode In doc.DocumentNode.Elements("//site")
        'my code to process each element here
        'not important because my app doesnt get this far lol
    Next

Catch ex as Exception
    Console.Writeline("Caught Exception: {0}", ex.Message)
End Try

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I am loading a text file, that contains about 1100 lines, and each line is going to be processed with HTML Agility Pack. From what I can tell, when it runs “doc.loadhtml(richtextbox1)”, it throws the error. I also have tried to load the file into a string, and load the string with “doc.loadhtml(thestring)”. It doesn’t make a difference, still errors.

Here are is a sample of how each line looks:

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<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />
<Site Index="" Name="" Group="" PR="" />

---

I am using HTML Agility Pack, however the above is what is on every line, about 1100 lines! For testing, I have a smaller text file made of about 50 lines before I load up the 1100 line file 😉 There aren’t any HTML, HEAD, or BODY tags! They aren’t needed for my parsing. I am using HTML Agility Pack because it is easy to parse elements with. I can grab each value easily from each line.

I am not sure if maybe the error is because it technically isn’t HTML? Meaning since the loaded code doesn’t have an HTML or BODY tag, that it errors? I wanted to get this question posted, and while I am waiting on some answers, I am going to parse the document another way. Just curious as to what the deal is and why HTML Agility Pack isn’t working. More of a proof of concept then anything, for my own learning and knowledge.

Here is the error I get (btw the on the doc.load() line, is where it throws the exception):

---

Object reference not set to an instance of an object

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Last Note: The routine is on a background thread. I have used multi-threading before, and have delegates created for deeper in the code. Maybe I am just overlooking something, I did write most of the code last night at like 3 am lol.

Answer 1

It looks like you’re not initializing the document…

Dim doc As HtmlDocument = Nothing

I don’t write VB, mostly C#, Java and C++, but doc = Nothing seems like doc = null and when you invoke the load(...) method on a null object, I would expect to see the “Object reference not set to an instance of an object” exception.

Try initializing the doc to an actual HtmlDocument:

Dim doc As New HtmlDocument