Extract information from Html using VB.net

Question

I'm working on extracting information from the html through vb. The html file looks like:

<div class='titlebar'><h1>Event Log started at 02/06/2015 13:07:30</h1></div>
<div class='Information'><h1>02/06/2015 13:09:30 | Log has opened</h1></div>
<div class='Interest'><h1>02/06/2015 13:13:03 | finished!</h1></div>
<div class='Interest'><h1>02/06/2015 13:17:12 | finished!</h1></div>
<div class='Interest'><h1>02/06/2015 13:21:35 | finished!</h1></div>
<div class='Interest'><h1>02/06/2015 13:24:58 | finished!</h1></div>
<div class='Warning'><h1>02/06/2015 17:04:33 | Failed to stop, retrying...</h1></div>
<div class='Warning'><h1>02/06/2015 17:04:56 | Error during mix

From this, I need to be able to extract information into different listbox's for class =interest, class=warning and class=information. So through my research I obtained the below code:

Private Function getHtml(ByVal Adress As String) As String
    Dim rt As String = ""
    Dim wRequest As WebRequest
    Dim wResponse As WebResponse
    Dim SR As StreamReader
    wRequest = WebRequest.Create(Adress)
    wResponse = wRequest.GetResponse
    SR = New StreamReader(wResponse.GetResponseStream)
    rt = SR.ReadToEnd
    SR.Close()
    Return rt
End Function

Private Sub btn_lookup_Click(sender As Object, e As EventArgs) Handles btn_lookup.Click
    TextBox2.Text = getHtml(TextBox1.Text)
End Sub

The above code will copy the whole source information into the textbox. Is it possible only copy the specific information. So for

 <div class='Interest'><h1>02/06/2015 13:24:58 | finished!</h1></div>

I need to copy 02/06/2015 13:24:58 | finished!

Is this possible?

Thank You

Tim Schmelter · Accepted Answer · 2016-01-06 10:09:03Z

1

I would suggest to use a HTML parser like HtmlAgilityPack:

Dim html As String = File.ReadAllText("C:\Temp\html.txt")
Dim doc As New HtmlAgilityPack.HtmlDocument()
doc.LoadHtml(html)
Dim interestDivs = doc.DocumentNode.SelectNodes("//div[contains(@class,'Interest')]")
Dim warningDivs = doc.DocumentNode.SelectNodes("//div[contains(@class,'Warning')]")
Dim informationDivs = doc.DocumentNode.SelectNodes("//div[contains(@class,'Information')]")

Dim lines = From div In interestDivs Select div.InnerText
lines = lines.Concat(From div In warningDivs Select div.InnerText)
lines = lines.Concat(From div In informationDivs Select div.InnerText)
TextBox2.Lines = lines.ToArray()

If you are more familiar with LINQ than XPath you can also use these queries:

Dim interests = From div In doc.DocumentNode.Descendants("div")
                Where div.GetAttributeValue("class", "") = "Interest"
                Select div.InnerText
Dim warnings = From div In doc.DocumentNode.Descendants("div")
               Where div.GetAttributeValue("class", "") = "Warning"
               Select div.InnerText
Dim infos = From div In doc.DocumentNode.Descendants("div")
            Where div.GetAttributeValue("class", "") = "Information"
            Select div.InnerText
TextBox2.Lines = interests.Concat(warnings).Concat(infos).ToArray()

edited Jan 6, 2016 at 10:09

answered Jan 6, 2016 at 9:56

Tim Schmelter

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6 Comments

Satvir Singh Over a year ago

Just to mention I'm only familiar with VB at begineer's level . I will be reading from Html, so if I changed html = "C:\Desktop\test.html" do I need to modify anything, because doing so gives me an error because Lines are Null.

Tim Schmelter Over a year ago

@SatvirSingh: the first line of my code shows how to read a text file. Just replace ReadAllText("C:\Temp\html.txt") with ReadAllText("C:\Desktop\test.html")

Satvir Singh Over a year ago

I modified your code a bit and now I can collect the data into the specific richtextboxes. Thank you for all the help

Tim Schmelter Over a year ago

@SatvirSingh: glad that you've got it working. If you have further questions ask. You can edit your question to provide your modifications if you want. But i think it's not needed for future readers.

Satvir Singh Over a year ago

I have another question. Sometimes the data is not available in the html so for example I want to verify if this lines.Concat(From div In warningDivs Select div.InnerText) is not Null. How would I write.

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