Obtener texto de un elemento de una web

j0lama · 1 Febrero 2015, 23:06 PM

Hola buenas mi duda es que como puedo hacer para que de una web, por ejemplo una web que muestre el IBEX 35, establecer en un label el valor que ha caido/subido el IBEX
es decir el texto que te da la web (valor de la caída) ponerlo en un label
Por favor expliquenmelo en c# que VB no se me da muy bien xD
Gracias

Eleкtro · 2 Febrero 2015, 02:12 AM

Buenas

Pasos a seguir:

1) Obtener el código fuente para parsearlo.

2) Encontrar el elemento que contiene el valor, mediante técnica XPATH o REGEX, y obtener el valor en cuestión, del Ibex en este caso.

Solo debes examinar el source minuciosamente para rastrear el xpath correcto. Te muestro un ejemplo real en VB.Net utilizando la librería HtmlAgilityPack, y también traducido a C# (quizás se traduzca incorrectamente):

vb.net

Código (vbnet) [Seleccionar]

Public Class Form1

    Private ReadOnly html As String =
        <a><![CDATA[
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<body>

 <div class="infolinks"><input type="hidden" name="IL_IN_TAG" value="1"/></div><div id="main">

  <div class="music">

   <h2 class="boxtitle">New releases \ <small>
    <a href="/newalbums" title="New releases mp3 downloads" rel="bookmark">see all</a></small>
   </h2>

   <div class="item">

       <div class="thumb">
     <a href="http://www.mp3crank.com/curt-smith/deceptively-heavy-121861" rel="bookmark" lang="en" title="Curt Smith - Deceptively Heavy album downloads"><img width="100" height="100" alt="Mp3 downloads Curt Smith - Deceptively Heavy" title="Free mp3 downloads Curt Smith - Deceptively Heavy" src="http://www.mp3crank.com/cover-album/Curt-Smith-Deceptively-Heavy-400x400.jpg"/></a>
       </div>

    <div class="release">
     <h3>Curt Smith</h3>
     <h4>
      <a href="http://www.mp3crank.com/curt-smith/deceptively-heavy-121861" title="Mp3 downloads Curt Smith - Deceptively Heavy">Deceptively Heavy</a>
     </h4>
     <script src="/ads/button.js"></script>
    </div>

    <div class="release-year">
     <p>Year</p>
     <span>2013</span>
    </div>

    <div class="genre">
     <p>Genre</p>
     <a href="http://www.mp3crank.com/genre/indie" rel="tag">Indie</a><a href="http://www.mp3crank.com/genre/pop" rel="tag">Pop</a>
    </div>

   </div>

   <div class="item">

       <div class="thumb">
     <a href="http://www.mp3crank.com/wolf-eyes/lower-demos-121866" rel="bookmark" lang="en" title="Wolf Eyes - Lower Demos album downloads"><img width="100" height="100" alt="Mp3 downloads Wolf Eyes - Lower Demos" title="Free mp3 downloads Wolf Eyes - Lower Demos" src="http://www.mp3crank.com/cover-album/Wolf-Eyes-–-Lower-Demos.jpg" /></a>
       </div>

    <div class="release">
     <h3>Wolf Eyes</h3>
     <h4>
      <a href="http://www.mp3crank.com/wolf-eyes/lower-demos-121866" title="Mp3 downloads Wolf Eyes - Lower Demos">Lower Demos</a>
     </h4>
     <script src="/ads/button.js"></script>
    </div>

    <div class="release-year">
     <p>Year</p>
     <span>2013</span>
    </div>

    <div class="genre">
     <p>Genre</p>
     <a href="http://www.mp3crank.com/genre/rock" rel="tag">Rock</a>
    </div>

   </div>

  </div>

 </div>

</body>
</html>
]]>$</a>.Value

    Private sb As New System.Text.StringBuilder

    Private htmldoc As HtmlAgilityPack.HtmlDocument = New HtmlAgilityPack.HtmlDocument
    Private htmlnodes As HtmlAgilityPack.HtmlNodeCollection = Nothing

    Private Title As String = String.Empty
    Private Cover As String = String.Empty
    Private Year As String = String.Empty
    Private Genres As String() = {String.Empty}
    Private URL As String = String.Empty

    Private Sub Test() Handles MyBase.Shown

        ' Load the html document.
        htmldoc.LoadHtml(html)

        ' Select the (10 items) nodes.
        ' All "SelectSingleNode" below will use this DIV element as a starting point.
        htmlnodes = htmldoc.DocumentNode.SelectNodes("//div[@class='item']")

        ' Loop trough the nodes.
        For Each node As HtmlAgilityPack.HtmlNode In htmlnodes

             ' Set the values:
            Title = node.SelectSingleNode(".//div[@class='release']/h4/a[@title]").GetAttributeValue("title", "Unknown Title")
            Cover = node.SelectSingleNode(".//div[@class='thumb']/a/img[@src]").GetAttributeValue("src", String.Empty)
            Year = node.SelectSingleNode(".//div[@class='release-year']/span").InnerText
            Genres = (From genre In node.SelectNodes(".//div[@class='genre']/a") Select genre.InnerText).ToArray
            URL = node.SelectSingleNode(".//div[@class='release']/h4/a[@href]").GetAttributeValue("href", "Unknown URL")

            ' Display the values:
            sb.Clear()
            sb.AppendLine(String.Format("Title : {0}", Title))
            sb.AppendLine(String.Format("Cover : {0}", Cover))
            sb.AppendLine(String.Format("Year  : {0}", Year))
            sb.AppendLine(String.Format("Genres: {0}", String.Join(", ", Genres)))
            sb.AppendLine(String.Format("URL   : {0}", URL))
            MsgBox(sb.ToString)

        Next node

    End Sub

End Class

c#:

Código (csharp) [Seleccionar]

using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
public class Form1
{


 private readonly string html = new XElement("a", new XCData("\n<!DOCTYPE html>\n<html xmlns=\"http://www.w3.org/1999/xhtml\" xml:lang=\"en\" lang=\"en\">\n<body>\n\n\t<div class=\"infolinks\"><input type=\"hidden\" name=\"IL_IN_TAG\" value=\"1\"/></div><div id=\"main\">\n\n\t\t<div class=\"music\">\n\n\t\t\t<h2 class=\"boxtitle\">New releases \\ <small>\n\t\t\t\t<a href=\"/newalbums\" title=\"New releases mp3 downloads\" rel=\"bookmark\">see all</a></small>\n\t\t\t</h2>\n\n\t\t\t<div class=\"item\">\n\n\t    \t\t<div class=\"thumb\">\n\t\t\t\t\t<a href=\"http://www.mp3crank.com/curt-smith/deceptively-heavy-121861\" rel=\"bookmark\" lang=\"en\" title=\"Curt Smith - Deceptively Heavy album downloads\"><img width=\"100\" height=\"100\" alt=\"Mp3 downloads Curt Smith - Deceptively Heavy\" title=\"Free mp3 downloads Curt Smith - Deceptively Heavy\" src=\"http://www.mp3crank.com/cover-album/Curt-Smith-Deceptively-Heavy-400x400.jpg\"/></a>\n\t    \t\t</div>\n\n\t\t\t\t<div class=\"release\">\n\t\t\t\t\t<h3>Curt Smith</h3>\n\t\t\t\t\t<h4>\n\t\t\t\t\t\t<a href=\"http://www.mp3crank.com/curt-smith/deceptively-heavy-121861\" title=\"Mp3 downloads Curt Smith - Deceptively Heavy\">Deceptively Heavy</a>\n\t\t\t\t\t</h4>\n\t\t\t\t\t<script src=\"/ads/button.js\"></script>\n\t\t\t\t</div>\n\n\t\t\t\t<div class=\"release-year\">\n\t\t\t\t\t<p>Year</p>\n\t\t\t\t\t<span>2013</span>\n\t\t\t\t</div>\n\n\t\t\t\t<div class=\"genre\">\n\t\t\t\t\t<p>Genre</p>\n\t\t\t\t\t<a href=\"http://www.mp3crank.com/genre/indie\" rel=\"tag\">Indie</a><a href=\"http://www.mp3crank.com/genre/pop\" rel=\"tag\">Pop</a>\n\t\t\t\t</div>\n\n\t\t\t</div>\n\n\t\t\t<div class=\"item\">\n\n\t    \t\t<div class=\"thumb\">\n\t\t\t\t\t<a href=\"http://www.mp3crank.com/wolf-eyes/lower-demos-121866\" rel=\"bookmark\" lang=\"en\" title=\"Wolf Eyes - Lower Demos album downloads\"><img width=\"100\" height=\"100\" alt=\"Mp3 downloads Wolf Eyes - Lower Demos\" title=\"Free mp3 downloads Wolf Eyes - Lower Demos\" src=\"http://www.mp3crank.com/cover-album/Wolf-Eyes-–-Lower-Demos.jpg\" /></a>\n\t    \t\t</div>\n\n\t\t\t\t<div class=\"release\">\n\t\t\t\t\t<h3>Wolf Eyes</h3>\n\t\t\t\t\t<h4>\n\t\t\t\t\t\t<a href=\"http://www.mp3crank.com/wolf-eyes/lower-demos-121866\" title=\"Mp3 downloads Wolf Eyes - Lower Demos\">Lower Demos</a>\n\t\t\t\t\t</h4>\n\t\t\t\t\t<script src=\"/ads/button.js\"></script>\n\t\t\t\t</div>\n\n\t\t\t\t<div class=\"release-year\">\n\t\t\t\t\t<p>Year</p>\n\t\t\t\t\t<span>2013</span>\n\t\t\t\t</div>\n\n\t\t\t\t<div class=\"genre\">\n\t\t\t\t\t<p>Genre</p>\n\t\t\t\t\t<a href=\"http://www.mp3crank.com/genre/rock\" rel=\"tag\">Rock</a>\n\t\t\t\t</div>\n\n\t\t\t</div>\n\n\t\t</div>\n\n\t</div>\n\n</body>\n</html>\n")).Value;

 private System.Text.StringBuilder sb = new System.Text.StringBuilder();
 private HtmlAgilityPack.HtmlDocument htmldoc = new HtmlAgilityPack.HtmlDocument();

 private HtmlAgilityPack.HtmlNodeCollection htmlnodes = null;
 private string Title = string.Empty;
 private string Cover = string.Empty;
 private string Year = string.Empty;
 private string[] Genres = { string.Empty };

 private string URL = string.Empty;

 private void Test()
 {
  // Load the html document.
  htmldoc.LoadHtml(html);

  // Select the (10 items) nodes.
  // All "SelectSingleNode" below will use this DIV element as a starting point.
  htmlnodes = htmldoc.DocumentNode.SelectNodes("//div[@class='item']");

  // Loop trough the nodes.

  foreach (HtmlAgilityPack.HtmlNode node in htmlnodes) {
   // Set the values:
   Title = node.SelectSingleNode(".//div[@class='release']/h4/a[@title]").GetAttributeValue("title", "Unknown Title");
   Cover = node.SelectSingleNode(".//div[@class='thumb']/a/img[@src]").GetAttributeValue("src", string.Empty);
   Year = node.SelectSingleNode(".//div[@class='release-year']/span").InnerText;
   Genres = (from genre in node.SelectNodes(".//div[@class='genre']/a")genre.InnerText).ToArray;
   URL = node.SelectSingleNode(".//div[@class='release']/h4/a[@href]").GetAttributeValue("href", "Unknown URL");

   // Display the values:
   sb.Clear();
   sb.AppendLine(string.Format("Title : {0}", Title));
   sb.AppendLine(string.Format("Cover : {0}", Cover));
   sb.AppendLine(string.Format("Year  : {0}", Year));
   sb.AppendLine(string.Format("Genres: {0}", string.Join(", ", Genres)));
   sb.AppendLine(string.Format("URL   : {0}", URL));
   Interaction.MsgBox(sb.ToString);

  }

 }
 public Form1()
 {
  Shown += Test;
 }

}

//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

Plus este util snippet para buscar y obtener todos los xpath de un archivo html, para que sea más facil de llevarlo a cabo:

vb.net:

Código (vbnet) [Seleccionar]

    ' Get Html XPaths
    ' By Elektro
    '
    ' Example Usage:
    '
    ' Dim Document As New HtmlAgilityPack.HtmlDocument
    ' Document.LoadHtml(IO.File.ReadAllText("C:\File.html"))
    ' Dim XpathList As List(Of String) = GetHtmlXPaths(Document)
    ' ListBox1.Items.AddRange((From XPath As String In XpathList Select XPath).ToArray)

    ''' <summary>
    ''' Gets all the XPath expressions of an <see cref="HtmlAgilityPack.HtmlDocument"/> document.
    ''' </summary>
    ''' <param name="Document">Indicates the <see cref="HtmlAgilityPack.HtmlDocument"/> document.</param>
    ''' <returns>List(Of System.String).</returns>
    Public Function GetHtmlXPaths(ByVal Document As HtmlAgilityPack.HtmlDocument) As List(Of String)

        Dim XPathList As New List(Of String)
        Dim XPath As String = String.Empty

        For Each Child As HtmlAgilityPack.HtmlNode In Document.DocumentNode.ChildNodes

            If Child.NodeType = HtmlAgilityPack.HtmlNodeType.Element Then
                GetHtmlXPaths(Child, XPathList, XPath)
            End If

        Next Child

        Return XPathList

    End Function

    ''' <summary>
    ''' Gets all the XPath expressions of an <see cref="HtmlAgilityPack.HtmlNode"/>.
    ''' </summary>
    ''' <param name="Node">Indicates the <see cref="HtmlAgilityPack.HtmlNode"/>.</param>
    ''' <param name="XPathList">Indicates a ByReffered XPath list as a <see cref="List(Of String)"/>.</param>
    ''' <param name="XPath">Indicates the current XPath.</param>
    Private Sub GetHtmlXPaths(ByVal Node As HtmlAgilityPack.HtmlNode,
                              ByRef XPathList As List(Of String),
                              Optional ByVal XPath As String = Nothing)

        XPath &= Node.XPath.Substring(Node.XPath.LastIndexOf("/"c))

        Const ClassNameFilter As String = "[@class='{0}']"
        Dim ClassName As String = Node.GetAttributeValue("class", String.Empty)

        If Not String.IsNullOrEmpty(ClassName) Then
            XPath &= String.Format(ClassNameFilter, ClassName)
        End If

        If Not XPathList.Contains(XPath) Then
            XPathList.Add(XPath)
        End If

        For Each Child As HtmlAgilityPack.HtmlNode In Node.ChildNodes

            If Child.NodeType = HtmlAgilityPack.HtmlNodeType.Element Then
                GetHtmlXPaths(Child, XPathList, XPath)
            End If

        Next Child

    End Sub

c#:

Código (csharp) [Seleccionar]


// Get Html XPaths
// By Elektro

/// <summary>
/// Gets all the XPath expressions of an <see cref="HtmlAgilityPack.HtmlDocument"/> document.
/// </summary>
/// <param name="Document">Indicates the <see cref="HtmlAgilityPack.HtmlDocument"/> document.</param>
/// <returns>List(Of System.String).</returns>
public List<string> GetHtmlXPaths(HtmlAgilityPack.HtmlDocument Document)
{

 List<string> XPathList = new List<string>();
 string XPath = string.Empty;


 foreach (HtmlAgilityPack.HtmlNode Child in Document.DocumentNode.ChildNodes) {
  if (Child.NodeType == HtmlAgilityPack.HtmlNodeType.Element) {
   GetHtmlXPaths(Child, ref XPathList, XPath);
  }

 }

 return XPathList;

}

/// <summary>
/// Gets all the XPath expressions of an <see cref="HtmlAgilityPack.HtmlNode"/>.
/// </summary>
/// <param name="Node">Indicates the <see cref="HtmlAgilityPack.HtmlNode"/>.</param>
/// <param name="XPathList">Indicates a ByReffered XPath list as a <see cref="List(Of String)"/>.</param>
/// <param name="XPath">Indicates the current XPath.</param>

private void GetHtmlXPaths(HtmlAgilityPack.HtmlNode Node, ref List<string> XPathList, string XPath = null)
{
 XPath += Node.XPath.Substring(Node.XPath.LastIndexOf('/'));

 const string ClassNameFilter = "[@class='{0}']";
 string ClassName = Node.GetAttributeValue("class", string.Empty);

 if (!string.IsNullOrEmpty(ClassName)) {
  XPath += string.Format(ClassNameFilter, ClassName);
 }

 if (!XPathList.Contains(XPath)) {
  XPathList.Add(XPath);
 }


 foreach (HtmlAgilityPack.HtmlNode Child in Node.ChildNodes) {
  if (Child.NodeType == HtmlAgilityPack.HtmlNodeType.Element) {
   GetHtmlXPaths(Child, ref XPathList, XPath);
  }

 }

}

//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

saludos

Test Foro de elhacker.net SMF 2.1

Obtener texto de un elemento de una web

j0lama

Eleкtro