The source skeleton
To conceptualize how a KDE application works, we'll first have a very close look at the source skeleton already provided by the Application Wizard. As we already saw, we're having a set of source and header files that build the initial code for the application and make it ready-to-run. Therefore, the easiest way to explain the code is to follow the implementation line by line as it is processed during executing the program until it enters the main event loop and is ready to accept user input. Then, we'll have a look at the functionality that enables user interaction and how certain things work. This is probably the best way to explain the framework and, as it is similar to almost all KDE applications, will enable you to read source codes from other projects as well; additionally, you will know where to change what part of the code to make your applications behave the way they are designed for.
As the application begins its execution with entering the main() function,
this will be the start for our code examination. The main() function of
KScribble is implemented in the file main.cpp and can also be found using the Class Browser
by selecting the "Global Functions" folder.
1 int main(int argc, char **argv)
2 {
3 KAboutData about("kscribble", I18N_NOOP("KScribble"), version, description,
4 KAboutData::License_GPL, "(C) 2002 Your Name", 0, 0, "you@you.com");
5 about.addAuthor( "Your Name", 0, "you@you.com" );
6 KCmdLineArgs::init(argc, argv, &about);
7 KCmdLineArgs::addCmdLineOptions(options);
8 KApplication app;
9
10 // register ourselves as a dcop client
11 app.dcopClient()->registerAs(app.name(), false);
12
13 // see if we are starting with session management
14 if (app.isRestored())
15 RESTORE(KScribble)
16 else
17 {
18 // no session.. just start up normally
19 KCmdLineArgs *args = KCmdLineArgs::parsedArgs();
20 if (args->count() == 0)
21 {
22 KScribble *widget = new KScribble;
23 widget->show();
24 }
25 else
26 {
27 int i = 0;
28 for (; i < args->count(); i++)
29 {
30 KScribble *widget = new KScribble;
31 widget->show();
32 widget->load(args->url(i));
33 }
34 }
35 args->clear();
36 }
37
38 return app.exec();
39 }
Now, what happens first is the usual creation of a KApplication object, but we've
added some KDE methods that set program and author information for this application.
Let's have a look at the constructor and see how this instance is called
1 KScribble::KScribble()
2 : KMainWindow( 0, "KScribble" ),
3 m_view(new KScribbleView(this)),
4 m_printer(0)
5 {
6 // accept dnd
7 setAcceptDrops(true);
8
9 // tell the KMainWindow that this is indeed the main widget
10 setCentralWidget(m_view);
11
12 // then, setup our actions
13 setupActions();
14
15 // and a status bar
16 statusBar()->show();
17
18 // allow the view to change the statusbar and caption
19 connect(m_view, SIGNAL(signalChangeStatusbar(const QString&)),
20 this, SLOT(changeStatusbar(const QString&)));
21 connect(m_view, SIGNAL(signalChangeCaption(const QString&)),
22 this, SLOT(changeCaption(const QString&)));
23
24 }
Notice that KScribble inherits the KMainWindow class - a
commonly used base class for KDE applications. We initialize a class called KScribbleView
as our central widget, create a KStatusBar via the statusBar()
method (line 16), and connect some signals and slots together.
