Development/Tutorials/Using KParts

How To Use KParts

Tutorial Series	Plugins and KParts
Previous	Tutorial 5 - Command line arguments
What's Next	n/a
Further Reading	KParts Documentation

Warning

This page needs a review and probably holds information that needs to be fixed.

Parts to be reviewed:

Port to KF5

Port to KF5 is WIP

Introduction

KPart technology is used in kde to reuse GUI components. The advantage that a KPart presents is that it comes with predefined toolbar actions. By using kparts in applications developers can spend less time implementing text editor or command line features, for example and just use a katepart or a konsolepart instead. KParts are also used with Plugin technology to embed applications inside another, such as integrating PIM applications into Kontact.

This tutorial will show you how to use a KPart in your application, and how to create your own KPart.

KParts consist of a .desktop file describing the KPart and a .so file containing the function names and code. The .desktop file resides in KDE's services directory, you can find it out like this:

#kf5-config --path services
/home/username/.local/share/kservices5/:/usr/share/kservices5/

The first kPart we describe is KatePart, an editor representing a typical ReadWritePart. A typical ReadOnlyPart would be konsolePart.

Using Katepart

Simple KDE applications use a MainWindow derived from KMainWindow (such as in previous tutorials). To use a KPart in an application, the MainWindow must instead be derived from KParts::MainWindow. This will then take care of integrating the toolbar and menu items of the kpart together.

The following code creates a KParts::MainWindow with a kpart inside it.

main.cpp

#include <QApplication>
#include <QUrl>
#include <QCommandLineParser>

#include <KAboutData>
#include <KCrash>
#include <KLocalizedString>

 
#include "mainwindow.h"
 
int main (int argc, char *argv[])
{
    QApplication application(argc, argv);

    KLocalizedString::setApplicationDomain("amazeing");
    KCrash::initialize();

    KAboutData aboutData( QStringLiteral("kparttut1"),
        i18n("KPart Tutorial 1"),
        QStringLiteral("0.1"),
        i18n("A MainWindow for a KatePart."),
        KAboutLicense::GPL,
        i18n("Copyright (c) 2019 Developer") );
 
    QCommandLineParser parser;
    aboutData.setupCommandLine(&parser);

    parser.process(application);
    aboutData.processCommandLine(&parser);

    const QStringList args = parser.positionalArguments();

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

    if(!args.isEmpty())
    {
        window->load(QUrl(args.first()));
    }

    return app.exec();
}

The main.cpp file is the same as that used in Tutorial 5 - Command line arguments. The only difference is in the details of the KAboutData.

mainwindow.h

#ifndef KPARTTUTORIAL1_H        
#define KPARTTUTORIAL1_H        
                                
#include <KParts/MainWindow> 
#include <QUrl> 
                                
/**                             
 * This is the application "Shell".  It has a menubar, toolbar, and
 * statusbar but relies on the "Part" to do all the real work.     
 *                                                                 
 * @short Application Shell                                        
 * @author Developer <[email protected]>                           
 * @version 0.1
 */
class MainWindow : public KParts::MainWindow
{
    Q_OBJECT
public:
    /**
     * Default Constructor
     */
    MainWindow();

    /**
     * Default Destructor
     */
    ~MainWindow() override = default;

public slots:
    /**
     * Use this method to load whatever file/URL you have
     */
    void load(const QUrl& url);

    /**
     * Use this method to display an openUrl dialog and
     * load the URL that gets entered
     */
    void load();

private:
    void setupActions();

private:
    KParts::ReadWritePart *m_part;
};

#endif // KPARTTUT1_H

The mainwindow.h file is very simple. The important thing to notice here is that the MainWindow class inherits from KParts::MainWindow.

mainwindow.cpp

#include "mainwindow.h"

#include <KActionCollection>
#include <KConfig>
#include <KEditToolBar>
#include <KShortcutsDialog>
#include <KMessageBox>
#include <KService>
#include <KStandardAction>
#include <KParts/ReadWritePart>

#include <QApplication>
#include <QFileDialog>
#include <QStatusBar>

MainWindow::MainWindow()
    : KParts::MainWindow( )
{

    // Setup our actions
    setupActions();

    //query the .desktop file to load the requested Part
    KService::Ptr service = KService::serviceByDesktopName
                           ("katepart");

    if (service) {
        m_part = service->createInstance<KParts::ReadWritePart>(0);

        if (m_part) {
            // tell the KParts::MainWindow that this is indeed
            // the main widget
            setCentralWidget(m_part->widget());

            setupGUI(ToolBar | Keys | StatusBar | Save);

            // and integrate the part's GUI with the shell's
            createGUI(m_part);
        } else{
            return;//return 1; 
        }
    } else {
        // if we couldn't find our Part, we exit since the Shell by
        // itself can't do anything useful
        KMessageBox::error(this, "service katepart not found");
        qApp->quit();
        // we return here, cause qApp->quit() only means "exit the
        // next time we enter the event loop...
        return;
    }
}

void MainWindow::load(const QUrl& url)
{
    m_part->openUrl(url);
}

void MainWindow::setupActions()
{
    KStandardAction::open(this, QOverload<>::of(&MainWindow::load), 
        actionCollection());
    KStandardAction::quit(qApp, &QApplication::closeAllWindows,
        actionCollection());
}

void MainWindow::load()
{
    load(QFileDialog::getOpenFileUrl());
}

The mainwindow.cpp file contains the implementation of MainWindow. The constructor of this class contains all the code used to load the KPart.

First it sets up the actions used by the main window (Open and Quit), and then sets up the gui elements to go with these items (toolbar items, menu items, keyboard shortcuts). Next is the standard code used to load the KPart. The createGUI method is responsible for merging the toolbars and menus of the KPart with the rest of the application.

kparttut1ui.rc

<!DOCTYPE kpartgui SYSTEM "kpartgui.dtd">
<kpartgui name="kparttut1" version="1">
<MenuBar>
  <Menu noMerge="1" name="file"><text>&amp;File</text>
    <Action name="file_open"/>
    <Separator/>
    <Merge/>
    <Separator/>
    <Action name="file_quit"/>
  </Menu>

  <Merge />
</MenuBar>
<ToolBar noMerge="1" name="mainToolBar"><text>Main Toolbar</text>
  <Action name="file_open"/>
  <Merge/>
</ToolBar>
</kpartgui>

The kparttut1ui.rc file is used to define how the actions in the part and the actions in the main window will be merged together. The <Merge /> element in the file menu for example indicates that any part containing actions in a file menu should list its parts after the file_open action and before the file_quit action.

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)

project(kparttut1)

set(QT_MIN_VERSION "5.15.0")
set(KF_MIN_VERSION "5.82.0")

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

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

find_package(Qt5 ${QT_MIN_VERSION} CONFIG REQUIRED COMPONENTS Core Gui Widgets)

find_package(KF5 ${KF_MIN_VERSION} REQUIRED COMPONENTS
    CoreAddons
    Crash
    DBusAddons
    DocTools
    I18n
    XmlGui
    TextEditor
    Parts
)

set(kparttut1_SRCS
   main.cpp
   mainwindow.cpp
)

add_executable(kparttut1 ${kparttut1_SRCS})

target_link_libraries(kparttut1 PUBLIC
    Qt5::Widgets
    KF5::CoreAddons
    KF5::Crash
    KF5::DBusAddons
    KF5::DocTools
    KF5::I18n
    KF5::XmlGui
    KF5::TextEditor
    KF5::Parts
)

########### install files ###############

install(TARGETS kparttut1 ${KDE_INSTALL_TARGETS_DEFAULT_ARGS})

install(FILES kparttut1ui.rc 
    DESTINATION  ${KDE_INSTALL_KXMLGUI5DIR}/kparttut)

feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)

The CMakeLists.txt file is very simple in this case.

Running the Application

After compiling, linking and installing the application with

mkdir build && cd build && cmake .. && make -j4 && make install

it can be executed with

kparttut1 filename

where filename is a text file to load. One of the source files would be a good example.

When the file loads you will have a full-featured kate editor running in its own window. All of the editor features of kate are available in the toolbars and menu.

You will notice that the 'Open' action you defined in the MainWindow class has also appeared in the toolbar and in the menu along with the 'Quit' action.

The next tutorial will deal with creating your own KParts for use (and reuse) in other applications.