Desenvolvimento/Tutoriais/Primeiro programa

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Olá Mundo
Tutorial Series   Tutorial para Iniciantes
Previous   C++, Qt, Building KDE
What's Next   Tutorial 2 - KXmlGuiWindow
Further Reading   CMake


Seu primeiro programa deve cumprimentar o mundo com um amigável "Hello World", e o que mais? Para isso, usaremos uma classe KMessageBox e personalizaremos um dos botões.


Para obter mais informações sobre qualquer classe que você encontre, você pode usar o mecanismo de busca 'kde'. Por exemplo, para procurar por informações sobre KMessageBox, apenas digite "kde:kmessagebox" no Konqueror, Rekonq ou KRunner, e você será levado para a documentação.

Você pode querer usar KDevelop ou QtCreator como IDE para seus projetos.

O Código

Todo o código que precisamos estará em um arquivo, main.cpp. Crie esse arquivo com o código abaixo:

#include <cstdlib>

<syntaxhighlight lang="cpp-qt">
#include <QApplication>
#include <QCommandLineParser>
#include <KAboutData>
#include <KLocalizedString>
#include <KMessageBox>

int main (int argc, char *argv[])
    QApplication app(argc, argv);

    KAboutData aboutData(
                         // The program name used internally. (componentName)
                         // A displayable program name string. (displayName)
                         i18n("Tutorial 1"),
                         // The program version string. (version)
                         // Short description of what the app does. (shortDescription)
                         i18n("Displays a KMessageBox popup"),
                         // The license this code is released under
                         // 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())
                         // The bug report email address
                         // (bugsEmailAddress = QLatin1String("[email protected]")
                         QStringLiteral("[email protected]"));
    aboutData.addAuthor(i18n("Name"), i18n("Task"), QStringLiteral("[email protected]"),
                         QStringLiteral(""), QStringLiteral("OSC Username"));

    QCommandLineParser parser;
    KGuiItem yesButton( i18n( "Hello" ), QString(),
                        i18n( "This is a tooltip" ),
                        i18n( "This is a WhatsThis help text." ) );

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

First we need to 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 Framework 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.

Então chegamos a KCmdLineArgs. Essa é a classe que se usaria para especificar uma linha de comando para, por exemplo, abrir o programa com um arquivo específico. No entanto, nesse tutorial, nós simplesmente iniciamos com o objeto KAboutData que nós criamos então podemos usar --version ou --author.

Assim criamos um objeto KApplication. Isso precisa ser feito uma vez em cada programa, já que é necessário para coisas como i18n.

Now we've done all the necessary 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.


You want to use CMake for your build environment. You provide a file CMakeLists.txt, CMake uses this file to generate all Makefiles out of it.


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

cmake_minimum_required(VERSION 3.0)

project (tutorial1)

set(QT_MIN_VERSION "5.3.0")
set(KF5_MIN_VERSION "5.2.0")

find_package(ECM 1.0.0 REQUIRED NO_MODULE)

include(KDECompilerSettings NO_POLICY_SCOPE)

# Find Qt modules
    Core    # QCommandLineParser, QStringLiteral
    Widgets # QApplication 

# Find KDE modules
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    WidgetsAddons   # KMessageBox

set(tutorial1_SRCS main.cpp)

add_executable(tutorial1 ${tutorial1_SRCS})



The find_package() function locates the package that you ask it for (in this case ECM, Qt5, or KF5) and sets some variables describing the location of the package's headers and libraries. ECM, or Extra CMake Modules, is required to import special CMake files and functions for building KDE applications.

Here we try to find the modules for Qt 5 and KDE Frameworks 5 required to build our tutorial. The necessary files are included by CMake so that the compiler can see them at build time. Minimum version numbers are set at the very top of CMakeLists.txt file for easier reference.

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 add_executable() to create an executable called tutorial1 from the source files listed in our tutorial1_SRCS variable. Afterwards, we link our executable to the necessary libraries using target_link_libraries() function. The line starting with install writes a default "install" target into the Makefile.

Make And Run

To compile, link and install your program, you must have several software installed, e.g. cmake, make and gcc-c++, and the Qt 5 and KDE Frameworks development files. To be sure you have everything, best follow this install guide.

While you can run CMake directly inside the source code directory itself, it is a best practice, and actually enforced in some KDE software, to use a separate build directory and run CMake from there:

mkdir build && cd build

You can invoke CMake and make manually:

cmake .. && make

And launch it with:


Moving On

Now you can move on to using KXmlGuiWindow.

This page was last edited on 24 August 2020, at 16:44. Content is available under Creative Commons License SA 4.0 unless otherwise noted.