Development/Tutorials/KIO Slaves/Using KIO Slaves in your Program

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In this chapter we write a simple browser to show how easy it is to use kioslaves in KDE 4. The browser will download the page and show the html sourcecode. It will not render html - remember this is a programming demo. The purpose of kioslaves is to have access to a given storage or data representation without the need for blocking calls. This is solved via QT's signal/slot mechanism: Once the data has arrived, e.g. from a web page, it triggers a signal. The signal is connected to the respective slot and can start processing the data.

The files


#include <QString>
#include <kapplication.h>
#include <kaboutdata.h>
#include <klocalizedstring.h>
#include <kmessagebox.h>
#include <kcmdlineargs.h>
#include <KMainWindow>
#include <browser.h>
int main (int argc, char *argv[])
  // KAboutData (const QByteArray &appName, const QByteArray &catalogName, const KLocalizedString &programName, const QByteArray &version,
  const QByteArray& ba=QByteArray("test");
  const KLocalizedString name=ki18n("myName");
  KAboutData aboutData( ba, ba, name, ba, name);
  KCmdLineArgs::init( argc, argv, &aboutData );
  KApplication khello;
  Browser *mw = new Browser();
The purpose of main is to create a Browser instance and hold it open while the KDE event loop is running (i.e. the KDE program is ready).
== browser.h == 
<syntaxhighlight lang="cpp-qt">
#ifndef KDE4START_H__
#define KDE4START_H__
#include <kmainwindow.h>
#include <kio/scheduler.h>
#include <kurl.h>
#include <kio/jobclasses.h>
class Browser : public QWidget
  public slots:
    void slotButtonClicked();
    void dataIsHere(KIO::Job *,const QByteArray &);
== browser.cpp ==
<syntaxhighlight lang="cpp-qt">
#include <kio/scheduler.h>
#include <kurl.h>
#include <kio/jobclasses.h>
#include <kdebug.h>
#include <browser.h>
class TransferJob;
Browser::Browser() : QWidget(NULL)
void Browser::slotButtonClicked()
  kDebug() << "entering function";
  // creating a kioslave
  KIO::TransferJob *job = KIO::get(KUrl(""));
  connect (job, SIGNAL(  data(KIO::Job *, const QByteArray & )), this, SLOT(dataIsHere(KIO::Job *,const QByteArray &)));
void Browser::dataIsHere(KIO::Job *,const QByteArray & data )
  kDebug() << "data is here";
  kDebug() << data;
As discussed, the Browser class does not do a busy wait for the data to arrive from the web. Instead, it uses the http kioslave's signal data by connecting it to the slot dataishere. <tt>dataIsHere</tt> gets the http transmission via its parameter data and just outputs it. That's it - no blocking, no busy wait!
== CMakeLists.txt ==
PROJECT( browser )
SET(kde4startSources main.cpp browser.cpp )
KDE4_ADD_EXECUTABLE(browser ${kde4startSources} )
= Kompile, link and run it =
 cmake . && make && ./browser

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