Trucos de Visual Basic.NET Extraer enlaces de una página Web

Para poder extraer los enlaces de una página web usaremos regular expressions.

Primero tendremos que realizar un proceso para que descargue la web y así poderla analizar.

En c#:
--------------------------------
using System;
using System.Data;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections;


public ArrayList UrlList(string url)
{

byte[] resultHTML;

ArrayList linksArray = new ArrayList();

WebClient myWebClient = new WebClient();

resultHTML = myWebClient.DownloadData(url);

UTF8Encoding utf8Enc = new UTF8Encoding();

string myResultString = utf8Enc.GetString(resultHTML);

myResultString= myResultString.ToLower();

Regex regularexpre = new Regex("href\\s*=\\s*(?:(?:\\\"(?[^\\\"]*)\\\")|(?[^\\s]* ))");

MatchCollection collectionUrls = regularexpre.Matches(myResultString);

foreach(Match res in collectionUrls)
{
foreach(Group t in res.Groups)
{
linksArray.Add(t.Value);
}
}

return linksArray;
}

En Visual Basic:
--------------------------------
Imports System
Imports System.Collections
Imports System.Data
Imports System.Net
Imports System.Text
Imports System.Text.RegularExpressions

Dim resultHTML As Byte()
Dim myWebClient As New Net.WebClient

If UrlLocal <> url Then '
resultHTML = myWebClient.DownloadData(UrlLocal & "/" & url)
Else
resultHTML = myWebClient.DownloadData(url)
End If

Dim utf8Enc As New UTF8Encoding

Dim myResultString As String = utf8Enc.GetString(resultHTML)

myResultString = myResultString.ToLower()

Dim regularexpre As New Regex("href\s*=\s*(?:(?:\""(?[^\""]*)\"")|(?[^\s]* ))")

Dim collectionUrls As MatchCollection
collectionUrls = regularexpre.Matches(myResultString)

Dim res As Match

For Each res In collectionUrls
Dim t As Group
For Each t In res.Groups
arrLinks.Add(t.value)
Next
Next

Código fuente extraído de www.programar.net