Development/Tutorials/First program/KF5

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Hello World

Tutorial Series	Beginner Tutorial
Previous	C++, Qt, Building KDE
What's Next	Tutorial 2 - KXmlGuiWindow
Further Reading	CMake

Abstract

Your first program shall greet the world with a friendly "Hello World", what else? For that, we will use a KMessageBox and customise one of the buttons.

Tip

To get more information about any class you come across, you can use the ‘kde’ search engine. For example, to look for information about KMessageBox, just type "kde:kmessagebox" into Konqueror, Rekonq or KRunner, and you’ll be taken to the documentation.

Tip

You might want to use KDevelop or QtCreator as IDE for your projects.

The Code

All the code we need will be in one file, main.cpp. Create that file with the code below:

#include <cstdlib>


#include <QApplication>
#include <QCommandLineParser>
#include <KAboutData>
#include <KLocalizedString>
#include <KMessageBox>

int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    KLocalizedString::setApplicationDomain("tutorial1");
    
    KAboutData aboutData(
                         // The program name used internally. (componentName)
                         QStringLiteral("tutorial1"),
                         // A displayable program name string. (displayName)
                         i18n("Tutorial 1"),
                         // The program version string. (version)
                         QStringLiteral("1.0"),
                         // Short description of what the app does. (shortDescription)
                         i18n("Displays a KMessageBox popup"),
                         // The license this code is released under
                         KAboutLicense::GPL,
                         // Copyright Statement (copyrightStatement = QString())
                         i18n("(c) 2015"),
                         // Optional text shown in the About box.
                         // Can contain any information desired. (otherText)
                         i18n("Some text..."),
                         // The program homepage string. (homePageAddress = QString())
                         QStringLiteral("http://example.com/"),
                         // The bug report email address
                         // (bugsEmailAddress = QLatin1String("[email protected]")
                         QStringLiteral("[email protected]"));
    aboutData.addAuthor(i18n("Name"), i18n("Task"), QStringLiteral("[email protected]"),
                         QStringLiteral("http://your.website.com"), QStringLiteral("OSC Username"));
    KAboutData::setApplicationData(aboutData);


    QCommandLineParser parser;
    parser.addHelpOption();
    parser.addVersionOption();
    aboutData.setupCommandLine(&parser);
    parser.process(app);
    aboutData.processCommandLine(&parser);
    
    KGuiItem yesButton( i18n( "Hello" ), QString(),
                        i18n( "This is a tooltip" ),
                        i18n( "This is a WhatsThis help text." ) );

    return 
        KMessageBox::questionYesNo 
        (0, i18n( "Hello World" ), i18n( "Hello" ), yesButton ) 
        == KMessageBox::Yes? EXIT_SUCCESS: EXIT_FAILURE;
}

Then we create a QApplication object. This needs to be done exactly once in each program since it is needed for things such as i18n. It also should be created before any other KDE or Qt object. A call to KLocalizedString::setApplicationDomain() is required to properly set the translation catalog and must be done before the next step happens.

The first KDE specific object we create 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. We then call KAboutData::setApplicationData() to initialize the properties of the QApplication object.

Then we come to QCommandLineParser. 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.

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 yesButton 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.

CMakeLists.txt

project (tutorial1)

#1
cmake_minimum_required(VERSION 2.8.12 FATAL_ERROR)
set(QT_MIN_VERSION "5.3.0")
set(KF5_MIN_VERSION "5.2.0")

#2
find_package(ECM 1.0.0 REQUIRED NO_MODULE)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH} ${ECM_KDE_MODULE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/cmake)

include(KDEInstallDirs)
include(KDECMakeSettings)
include(KDECompilerSettings)
include(FeatureSummary)

# Find Qt modules
find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS 
    Core    # QCommandLineParser, QStringLiteral
    Widgets # QApplication 
)

# Find KDE modules
find_package(KF5 ${KF5_MIN_VERSION} REQUIRED COMPONENTS
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    WidgetsAddons   # KMessageBox
)

feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
    
set(tutorial1_SRCS main.cpp)

# just plain add_executable
add_executable(tutorial1 ${tutorial1_SRCS})

# module-based linking
target_link_libraries(tutorial1
    Qt5::Widgets
    KF5::CoreAddons
    KF5::I18n
    KF5::WidgetsAddons
)

install(TARGETS tutorial1  ${INSTALL_TARGETS_DEFAULT_ARGS})

Notes