Development/Tutorials/First program (es)

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Hola Mundo
Serie   Tutorial para principiantes
Requisitos previos   C++, Qt, Entorno de desarrollo en KDE4
Siguiente   Tutorial 2 - KXmlGuiWindow
Lectura avanzada   CMake


Tu primer programa consistirá en saludar al mundo con el amigable "Hola Mundo", Para ellor, usaremos KMessageBox y personalizaremos uno de los botones.

Si deseas obtener más información respecto a cualquier clase con la que te topes, Konqueror te ofrece un acceso rápido. Por ejemplo, si estás buscando información sobre KMessageBox, simplemente teclea "kde:kmessagebox" en la barra de direcciones de Konqueror y éste te llevará a la documentación.

Quizas quieras usar KDevelop para tus proyectos, ya que ofrece muchas ventajas como completado de código, fácil acceso a la documentación de la API o soporte para depurar.

Lee este tutorial para configurar correctamente KDevelop para esta tarea. Probablemente querrás comprobar si la configuración es correcta abriendo primero una aplicación en KDE4 que ya exista.

Quizá necesites editar los archivos CMake a mano.

El Código

Todo el Código Fuente que necesitaremos estará en un solo archivo, que se llamará: main.cpp.. Crea este archivo con el siguiente código:

  1. include <KApplication>
  2. include <KAboutData>
  3. include <KCmdLineArgs>
  4. include <KMessageBox>

int main (int argc, char *argv[]) {

   KAboutData aboutData(
                        // The program name used internally.
                        // The message catalog name
                        // If null, program name is used instead.
                        // A displayable program name string.
                        ki18n("Tutorial 1"),
                        // The program version string.
                        // Short description of what the app does.
                        ki18n("Displays a KMessageBox popup"),
                        // The license this code is released under
                        // Copyright Statement
                        ki18n("(c) 2007"),
                        // Optional text shown in the About box.
                        // Can contain any information desired.
                        ki18n("Some text..."),
                        // The program homepage string.
                        // The bug report email address
                        "[email protected]");
   KCmdLineArgs::init( argc, argv, &aboutData );
   KApplication app;
   KGuiItem yesButton( i18n( "Hello" ), QString(),
                       i18n( "This is a tooltip" ),
                       i18n( "This is a WhatsThis help text." ) );
   KMessageBox::questionYesNo( 0, i18n( "Hello World" ),
                               i18n( "Hello" ), yesButton );

} The first KDE specific code we come across in this program is KAboutData. This is the class used to store information about the program such as a short description, authors or license information. Pretty much every KDE application should use this class.

Then we come to KCmdLineArgs. This is the class one would use to specify command line switches to, for example, open the program with a specific file. However, in this tutorial, we simply initialise it with the KAboutData object we created so we can use the --version or --author switches.

Then we create a KApplication object. This needs to be done exactly once in each program since it is needed for things such as i18n.

Now we've done all the necessary KDE setup, we can move on to doing interesting things with our application. We're going to create a popup box but we're going to customise one of the buttons. To do this customisation, we need to use a KGuiItem object. The first argument in the KGuiItem constructor is the text that will appear on the item (in our case, a button). Then we have an option of setting an icon for the button but we don't want one so we just give it QString(). We then set the tooltip (what appears when you hover over an item) and finally the "What's This?" (accessed through right-clicking or Shift-F1) text.

Now we have our item, we can create our popup. We call the KMessageBox::questionYesNo() function which, by default, creates a message box with a "Yes" and a "No" button. The second argument is the text that will appear in the message box above the buttons. The third is the caption the window will have and finally we set the KGuiItem for (what would normally be) the "Yes" button to the KGuiItem guiItem we created.

Note that all user-visible text is passed through the i18n() function; this is necessary for the UI to be translatable. More information on localization can be found in the localization tutorial.

We're all done as far as the code is concerned. Now to build it and try it out.


If you set up your environment as described in Getting Started/Build/KDE4, you can compile this code with

g++ main.cpp -o tutorial1 \
-I$QTDIR/include/Qt \
-I$QTDIR/include/QtCore \
-I$QTDIR/include \
-I$KDEDIR/include/KDE \
-I$KDEDIR/include \
-L$KDEDIR/lib \
-L$QTDIR/lib -lQtCore -lQtGui -lkdeui -lkdecore

and then run it with

dbus-launch ./tutorial1

On some platforms, the libraries might have to be linked with -lQtCore4 and -lQtGui4.

If you are using a packaged Qt, you might have no single QTDIR. Adjust the paths accordingly in this case. Or just move on to the next section. :-D

      • The above is not correct. QTDIR is defined for Qt 3 only. Use cmake -query or pkg-config to get the paths you're after. KDEDIR is even deprecated since KDE 3. Using kde4-config is the way to go, e.g. "kde4-config --expandvars --install include".

Using CMake

If that worked, you may want to use CMake, just like the rest of KDE. This will automatically locate the libraries and headers for KDE, Qt etc. and will allow you to easily build your applications on other computers.


Create a file named CMakeLists.txt in the same directory as main.cpp with this content: project (tutorial1)

find_package(KDE4 REQUIRED) include_directories(${KDE4_INCLUDES})

set(tutorial1_SRCS main.cpp)

kde4_add_executable(tutorial1 ${tutorial1_SRCS}) target_link_libraries(tutorial1 ${KDE4_KDEUI_LIBS}) The find_package() function locates the package that you ask it for (in this case KDE4) and sets some variables describing the location of the package's headers and libraries. In this case we will use the KDE4_INCLUDES variable which contains the path to the KDE4 header files.

In order to allow the compiler to find these files, we pass that variable to the include_directories() function which adds the KDE4 headers to the header search path.

Next we create a variable called tutorial1_SRCS using the set() function. In this case we simply set it to the name of our only source file.

Then we use kde4_add_executable() to create an executable called tutorial1 from the source files listed in our tutorial1_SRCS variable. Finally we link our executable to the KDE4 kdeui library using target_link_libraries() and the KDE4_KDEUI_LIBS variable which was set by the find_package() function.

Make And Run

You can invoke CMake and make manually:

mkdir build && cd build
cmake .. # Note the two dots - this is no ellipsis, but "parent directory".

Or, if you set up your environment as described in Getting Started/Build/KDE4, you can compile this code with:


And launch it with:


Moving On

Now you can move on to using KXmlGuiWindow.

Content is available under Creative Commons License SA 4.0 unless otherwise noted.