Creating the main window

#Summary

This step continues the Hello World project and introduces the KXmlGuiWindow class.

In the previous step, the program showed a dialog. Now we start building a working application with a full main window.

#KXmlGuiWindow

KXmlGuiWindow provides a complete main window with menu bar, toolbars, status bar and a central area for one large widget. The Help menu, for example, is already defined. Most applications built on SonicDE's libraries derive from it, because it lets you define menu and toolbar layouts in XML files (that technology is KXmlGui). We won't use that yet; the next step does.

To use KXmlGuiWindow, subclass it. Create two files, mainwindow.cpp and mainwindow.h, for the code.

#mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <KXmlGuiWindow>

class KTextEdit;

class MainWindow : public KXmlGuiWindow
{
public:
    explicit MainWindow(QWidget *parent = nullptr);

private:
    KTextEdit *textArea;
};

#endif // MAINWINDOW_H

First we subclass KXmlGuiWindow with class MainWindow : public KXmlGuiWindow, then declare the constructor, MainWindow(QWidget *parent = nullptr);.

Finally we declare a pointer to the object that makes up most of the program and turns it into a text editor: a KTextEdit, a rich text editing widget with extras such as hiding the mouse cursor while typing and spell checking.

#mainwindow.cpp

#include <KTextEdit>
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : KXmlGuiWindow(parent)
{
    textArea = new KTextEdit();
    setCentralWidget(textArea);
    setupGUI();
}

First, include the header with the class declaration.

In the constructor we create the KTextEdit textArea. Because it is a QWidget and our window is a QMainWindow (KXmlGuiWindow derives from it), we can call QMainWindow::setCentralWidget() to make textArea fill the central area of the window.

Finally, KXmlGuiWindow::setupGUI() does a lot behind the scenes and creates the default menus (Settings, Help).

#Back to main.cpp

To show the window, add a few lines to main.cpp:

#include <QApplication>
#include <QCommandLineParser>
#include <KAboutData>
#include <KLocalizedString>
#include "mainwindow.h"

int main (int argc, char *argv[])
{
    using namespace Qt::Literals::StringLiterals;

    QApplication app(argc, argv);
    KLocalizedString::setApplicationDomain("mainwindow");

    KAboutData aboutData(
        u"mainwindow"_s,
        i18n("Main Window"),
        u"1.0"_s,
        i18n("A simple text area"),
        KAboutLicense::GPL,
        i18n("(c) 2024"),
        i18n("Educational application..."),
        u"https://example.com/mainwindow/"_s,
        u"https://example.com/mainwindow/bugs/"_s);

    aboutData.addAuthor(
        i18n("John Doe"),
        i18n("Tutorial learner"),
        u"john.doe@example.com"_s,
        u"https://john-doe.example.com"_s,
        u"johndoe"_s);

    KAboutData::setApplicationData(aboutData);

    QCommandLineParser parser;
    aboutData.setupCommandLine(&parser);
    parser.process(app);
    aboutData.processCommandLine(&parser);

    MainWindow *window = new MainWindow();
    window->show();

    return app.exec();
}

We include the new header mainwindow.h, create a MainWindow near the end of main(), and show it (new windows are hidden by default).

#CMake

Add mainwindow.cpp to the sources, add the XmlGui and TextWidgets frameworks, and replace helloworld with mainwindow.

#CMakeLists.txt

cmake_minimum_required(VERSION 3.20)

project(mainwindow)

set(QT_MIN_VERSION "6.6.0")
set(KF_MIN_VERSION "6.0.0")

find_package(ECM ${KF_MIN_VERSION} REQUIRED NO_MODULE)
set(CMAKE_MODULE_PATH ${ECM_MODULE_PATH} ${CMAKE_CURRENT_SOURCE_DIR}/cmake)

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

find_package(Qt6 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS
    Core    # QCommandLineParser, QStringLiteral
    Widgets # QApplication
)

find_package(KF6 ${KF_MIN_VERSION} REQUIRED COMPONENTS
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    XmlGui          # KXmlGuiWindow
    TextWidgets     # KTextEdit
)

add_executable(mainwindow)

target_sources(mainwindow
    PRIVATE
    main.cpp
    mainwindow.cpp
)

target_link_libraries(mainwindow
    Qt6::Widgets
    KF6::CoreAddons
    KF6::I18n
    KF6::XmlGui
    KF6::TextWidgets
)

install(TARGETS mainwindow ${KDE_INSTALL_TARGETS_DEFAULT_ARGS})

feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)

#Running the application

Build and install it as in Hello World, then run:

mainwindow

Next: Using actions.