CS001496 - Gather data from web page with JavaScript, WebKit, and Qt

Overview

This snippet demonstrates how you can gather data from a web page to Qt via WebKit. We will use the CS001495 - Display local web page with Qt WebKit article as base for this snippet.

Preconditions

Read CS001495 - Display local web page with Qt WebKit

Code

html/view.html

We'll add two JavaScript includes in the head tag.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
  <head>
    <!-- You reference the resources with qrc:// -->
    <!-- Stylesheet reference -->
    <link rel="stylesheet" href="qrc:///css/view.css" />
    <!-- jQuery include -->
    <script type="text/javascript" src="qrc:///js/jquery.js" />
    <!-- Our own script include -->
    <script type="text/javascript" src="qrc:///js/script.js" />
 
    <title>WebKit example</title>
  </head>
  <body>
    <!-- Header -->
    <h1 id="header">Welcome</h1>
    <!-- Paragraph -->
    <p id="paragraph">Hello World!</p>
    <!-- Form -->
    <form id="form" action="#">
      <fieldset>
        <label for="text">Text</label>
        <!-- Text input -->
        <input id="text" type="text" />
        <!-- Submit button -->
        <input id="button" type="button" value="Submit!"/>
      </fieldset>
    </form>
  </body>
</html>

js/jquery.js

This js file is a reference to a JavaScript library called jQuery. You can obtain it here: http://docs.jquery.com/Downloading_jQuery#Download_jQuery

jQuery enables you to be more productive when writing JavaScript.

js/script.js

This file includes JavaScript which is used to create animations and dynamically add content to the site from the web page.

/**
  * Adds p element after the element which has paragraph as the id
  * with the content from input element with text as the id.
  * This is jQuery syntax: http://www.jquery.com
  *
  * $("#paragraph") documented here: http://docs.jquery.com/Selectors/id#id
  * .after documented here: http://docs.jquery.com/Manipulation/after
  * .val documented here: http://docs.jquery.com/Val
  */
button_click = function(event) {
    $("#paragraph").after("<p>" + $("#text").val() + "</p>");
}
 
/**
  * This is run after the the web page has been rendered.
  * $(document).ready documented here:
  * http://docs.jquery.com/Tutorials:Introducing_$(document).ready()
  */
$(document).ready(function(){
    /*
     * Hides all the h1 elements.
     * Element selector: http://docs.jquery.com/Selectors/element#element
     * hide function: http://docs.jquery.com/Hide
     */
    $("h1").hide();
    /*
     * Hides all the p elements.
     */
    $("p").hide();
    /*
     * Hides element with form id.
     */
    $("#form").hide();
    /*
     * Shows all the h1 elements with animation.
     * show function: http://docs.jquery.com/Show
     */
    $("h1").show('slow');
    /*
     * Shows all the p elements with animation.
     */
    $("p").show('slow');
    /*
     * Shows the element with form as id with animation.
     */
    $("#form").show('slow');
    /*
     * Adds button_click as click event handler
     * for element with button as id.
     * click function: http://docs.jquery.com/Events/click
     */
    $("#button").click(button_click);
});

src/gather-data.js

/**
  * Gathers all the text content from p elements
  * to an array and returns it.
  */
Qt_QWET_gather = function() {
  a = [];
  e = document.getElementsByTagName('p');
  for(var i = 0; i < e.length; i++) {
    a.push(e[i].textContent);
  }
  return a;
};
Qt_QWET_gather();

Add these files to the resources file and include the resource file in your project file as explained in CS001503 - Using resources in Qt.

The following code demonstrates how to read data from the web page via JavaScript executed from Qt.

src/qwet.h

The only things added to the header file in comparison to CS001495 - Display local web page with Qt WebKit are includes, the gatherButtonClicked slot, helper methods, and a reference to QListWidget which is used to display the gathered data.

#ifndef QWET_H
#define QWET_H
 
#include <QtCore/QPointer>
#include <QtCore/QFile>
#include <QtCore/QTextStream>
#include <QtCore/QVariant>
#include <QtCore/QList>
 
#include <QtWebKit/QWebView>
#include <QtWebKit/QWebPage>
#include <QtWebKit/QWebFrame>
 
#include <QtGui/QWidget>
#include <QtGui/QMainWindow>
#include <QtGui/QFrame>
#include <QtGui/QVBoxLayout>
#include <QtGui/QListWidget>
#include <QtGui/QPushButton>
 
class QWET : public QMainWindow
{
    Q_OBJECT
 
public:
    QWET(QWidget *parent = 0);
    ~QWET();
 
private slots:
    void gatherButtonClicked();
private:
    QPointer<QWebView> _webView;
    QPointer<QVBoxLayout> _layout;
    QPointer<QListWidget> _pList;
 
    QString _gatherJS;
 
    void setupUI();
 
    QString readFileToQString(const QString& fileName) const;
    void updatePList(QListWidget* widget,
                     const QList<QVariant>& values);
};
 
#endif // QWET_H

src/qwet.cpp

#include "qwet.h"
 
QWET::QWET(QWidget *parent) : QMainWindow(parent) 
{
    setupUI();
}
 
QWET::~QWET() 
{
}
 
void QWET::setupUI() 
{
    /**
      * Create the central widget
      * and set it.
      */
    QFrame* cW = new QFrame(this);
    setCentralWidget(cW);
 
    /**
      * Set the layout to central widget.
      */
    _layout = new QVBoxLayout(this);
    cW->setLayout(_layout);
    _layout->setMargin(0);
    _layout->setSpacing(0);
 
    /**
      * Let's create the web view which
      * will be used to display our page
      * with which we will be communicating with.
      */
    _webView = new QWebView(this);
    _webView->load(QUrl("qrc:///html/view.html"));
    _webView->show();
 
    /** Add it to layout */
    _layout->addWidget(_webView);
 
    /** We'll gather the results to list widget.  */
    _pList = new QListWidget(this);
    _layout->addWidget(_pList);
 
    /** Add the gather text button */
    QPushButton* gatherButton = new QPushButton("Gather text.", this);
    connect(gatherButton, SIGNAL(clicked()),
            this, SLOT(gatherButtonClicked()));
 
    _layout->addWidget(gatherButton);
}
 
/**
  * This slot gathers the p text content from the html page
  * and adds it to the the list widget.
  */
void QWET::gatherButtonClicked() 
{
    /**
      * Read the java script to be executed to a string.
      */
    if(this->_gatherJS.isEmpty()) {
        this->_gatherJS = this->readFileToQString(QString(":/js/gather-data.js"));
    }
    else {
        this->_gatherJS = "Qt_QWET_gather();";
    }
    /** Run the java script on the page and get results. */
    QVariant variant = this->_webView->page()->mainFrame()->evaluateJavaScript(this->_gatherJS);
    /** We make sure that the results are there. */
    if(!variant.isNull() &&
       variant.type() == QVariant::List) {
        /** Ask for the acual list we're expecting. */
        QList<QVariant> list = variant.toList();
        /** Update the entries in the list widget.*/
        this->updatePList(this->_pList.data(), list);
    }
}
 
/**
  * This function updates list widgets entries
  */
void QWET::updatePList(QListWidget* widget, const QList<QVariant>& values) 
{
    /** Check that the parameters are valid. */
    if(widget != 0 &&
       !values.isEmpty()) {
        /** Clear the entries. */
        widget->clear();
        /** Go through the values...*/
        QListIterator<QVariant> i(values);
        while(i.hasNext()) {
            QVariant v = i.next();
            /** ...and add them to widget. */
            widget->addItem(v.toString());
        }
    }
}
 
/**
  * Reads file to a string.
  */
QString QWET::readFileToQString(const QString& fileName) const 
{
    QFile file(fileName);
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return QString();
 
    QTextStream in(&file);
    QString content = in.readAll();
    file.close();
    return content;
}

Postconditions

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