Development/Tutorials/Using KActions/KF5

From KDE TechBase
How To Use KActions and XMLGUI
Tutorial Series   Beginner Tutorial
Previous   Tutorial 2 - KXmlGuiWindow, Basic XML knowledge
What's Next   Tutorial 4 - Saving and loading
Further Reading   None

Abstract

This tutorial introduces the concept of actions. Actions are a unified way of supplying the user with ways to interact with your program.

For example, if we wanted to let the user of Tutorial 2 clear the text box by clicking a button in the toolbar, from an option in the File menu or through a keyboard shortcut, it could all be done with one QAction.

KAction

A QAction is an object which contains all the information about the icon and shortcuts that is associated with a certain action. The action is then connected to a slot which carries out the work of your action.

The Code

main.cpp

#include <cstdlib>
 
#include <QApplication>
#include <QCommandLineParser>

#include <KAboutData>
#include <KLocalizedString>

#include "mainwindow.h"
 
int main (int argc, char *argv[])
{
    QApplication app(argc, argv);
    KLocalizedString::setApplicationDomain("tutorial3");
    
    KAboutData aboutData(
                         // The program name used internally. (componentName)
                         QStringLiteral("tutorial3"),
                         // A displayable program name string. (displayName)
                         i18n("Tutorial 3"),
                         // The program version string. (version)
                         QStringLiteral("1.0"),
                         // Short description of what the app does. (shortDescription)
                         i18n("A simple text area using KAction etc."),
                         // 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);
    
    MainWindow* window = new MainWindow();
    window->show();
    
    return app.exec();
}

This time, very little has changed in main.cpp, only the KAboutData constructor has been updated to show that we are now on tutorial 3.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <KXmlGuiWindow>

class KTextEdit;
 
class MainWindow : public KXmlGuiWindow
{
  public:
    MainWindow(QWidget *parent=0);
 
  private:
    KTextEdit* textArea;
    void setupActions();
};
 
#endif

Only a function void setupActions() has been added which will do all the work setting up the QActions.

mainwindow.cpp

#include <QApplication>
#include <QAction>

#include <KTextEdit>
#include <KLocalizedString>
#include <KActionCollection>
#include <KStandardAction>

#include "mainwindow.h"

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

void MainWindow::setupActions()
{
    QAction* clearAction = new QAction(this);
    clearAction->setText(i18n("&Clear"));
    clearAction->setIcon(QIcon::fromTheme("document-new"));
    actionCollection()->setDefaultShortcut(clearAction, Qt::CTRL + Qt::Key_W);
    actionCollection()->addAction("clear", clearAction);
    connect(clearAction, SIGNAL(triggered(bool)), textArea, SLOT(clear()));
    
    KStandardAction::quit(qApp, SLOT(quit()), actionCollection());
    
    setupGUI(Default, "tutorial3ui.rc");
}

Explanation

This builds upon the KXmlGuiWindow code from Tutorial 2. Most of the changes are to mainwindow.cpp, an important structural change being that the constructor for MainWindow now calls setupActions() instead of setupGUI(). setupActions() is where the new QAction code goes before finally calling setupGUI() itself.

Creating the QAction object

The QAction is built up in a number of steps. The first is including the QAction header and then creating the QAction: 

#include <QAction>
...
QAction* clearAction = new QAction(this);

This creates a new QAction called clearAction.

Setting QAction Properties

Text

Now that we have our QAction object, we can start setting its properties. The following code sets the text that will be displayed in the menu and under the QAction's icon in the toolbar. 

clearAction->setText(i18n("&Clear"));

Note that the text is passed through the i18n() function; this is necessary for the UI to be translatable (more information on this can be found in the i18n tutorial).

The text of the action should contain a & because that makes it easier to translate in non-latin1 languages. In Japanese, the translation might be ソース(&S) and without the & in the english text the translators cannot know if they have to add a & or not.

Icon

If the action is going to be displayed in a toolbar, it is nice to have an icon depicting the action. The following code sets the icon to the standard the document-new icon through the use of the setIcon() function: 

clearAction->setIcon(QIcon::fromTheme("document-new"));

Keyboard Shortcut

Setting a keyboard shortcut to perform our action is equally simple: 

actionCollection()->setDefaultShortcut(clearAction, Qt::CTRL + Qt::Key_W);

This associates Ctrl+W with the QAction.

Adding to the Collection

In order for the action to be accessed by the XMLGUI framework (explained in depth later) it must be added to the application's action collection. The action collection is accessed via the actionCollection() function like this: 

actionCollection()->addAction("clear", clearAction);

Here, the clearAction QAction is added to the collection and given a name of clear. This name (clear) is used by the XMLGUI framework to refer to the action, ergo, it should not be localized, since it is used internally only.

Connecting the action

Now that the action is fully set up, it needs to be connected to something useful. In this case (because we want to clear the text area), we connect our action to the clear() action belonging to a KTextEdit (which, unsurprisingly, clears the KTextEdit) 

connect( clearAction, SIGNAL( triggered(bool) ), 
         textArea, SLOT( clear() ) );

KStandardAction

For actions which would likely appear in almost every KDE application such as 'quit', 'save', and 'load' there are pre-created convenience QActions, accessed through Template:Kde.

They are very simple to use. Once the library has been included (#include <KStandardAction>), simply supply it with what you want the function to do and which QActionCollection to add it to. For example: 

KStandardAction::quit(qApp, SLOT(quit()), actionCollection());

Here we call the QApplicaton's quit method whenever the KStandardAction quit is triggered. We are able to access that QApplication method via the qApp macro.

In the end, this creates a QAction with the correct icon, text and shortcut and even adds it to the File menu.

Adding the action to menus and toolbars

At the moment, the new "Clear" action has been created but it hasn't been associated with any menus or toolbars. This is done with a KDE technology called XMLGUI, which does nice things like movable toolbars for you.

Defining your own help menu

The help menu is god-given, that is why all KDE help menus look the same. If you want to create your own help menu, search for the explanation around showAboutApplication() in from the KHelpMenu class in XMLGUI.

XMLGUI

appnameui.rc file

tutorial3ui.rc

<?xml version="1.0" encoding="UTF-8"?>
<gui name="tutorial3"
     version="1"
     xmlns="http://www.kde.org/standards/kxmlgui/1.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.kde.org/standards/kxmlgui/1.0
                         http://www.kde.org/standards/kxmlgui/1.0/kxmlgui.xsd" >
 
  <MenuBar>
    <Menu name="file" >
      <Action name="clear" />
    </Menu>
    <Menu >
      <text>A&amp;nother Menu</text>
      <Action name="clear" />
    </Menu >
  </MenuBar>
 
  <ToolBar name="mainToolBar" >
    <text>Main Toolbar</text>
    <Action name="clear" />
  </ToolBar>
 
</gui>

CMake

CMakeLists.txt

project (tutorial3)

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

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, QAction
)

# Find KDE modules
find_package(KF5 ${KF5_MIN_VERSION} REQUIRED COMPONENTS
    CoreAddons      # KAboutData
    I18n            # KLocalizedString
    XmlGui          # KXmlGuiWindow, KActionCollection
    TextWidgets     # KTextEdit
    ConfigWidgets   # KStandardActions
)
    

feature_summary(WHAT ALL INCLUDE_QUIET_PACKAGES FATAL_ON_MISSING_REQUIRED_PACKAGES)
    
set(tutorial3_SRCS main.cpp mainwindow.cpp)

# just plain add_executable
add_executable(tutorial3 ${tutorial3_SRCS})

# module-based linking
target_link_libraries(tutorial3
    Qt5::Widgets
    KF5::CoreAddons
    KF5::I18n
    KF5::XmlGui
    KF5::TextWidgets
    KF5::ConfigWidgets
)

install(TARGETS tutorial3  ${INSTALL_TARGETS_DEFAULT_ARGS})
# 1
install(FILES tutorial3ui.rc DESTINATION ${KXMLGUI_INSTALL_DIR}/tutorial3)

Notes

  1. .ui files now installed to {KXMLGUI_INSTALL_DIR - https://community.kde.org/Frameworks/Porting_Notes#General

Moving On

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