KDE Frameworks
The KDE Frameworks, currently version 5 or KF5, is a collection of 80 libraries that are built on top of the Qt application framework and provides everything from utility classes to asynchronous and network-transparent I/O to additional data model and widgets to desktop-centric integration. If Qt itself doesn't provide a certain functionality or feature, chances are, there's a KDE Framework for that.
While KF5 does serve as the most basic building blocks of KDE software, they can be used by any Qtx application just like any third-party Qt add-on library. Just like any other KDE software, KF5 uses and favors a CMake build system but all frameworks support QMake as well. Many frameworks are available on multiple desktop operating systems such as Linux and Windows and are even available on Android. Be sure to check each framework's documentation for their supported platforms.
Guarantees and License
KDE, of course, takes software quality seriously but even more so when it comes to KF5. The Frameworks come with quality promises and to make sure you won't need to wait for your favorite bug to get fixed, a new version is released monthly. And since it's free software developed in an open environment, anyone can participate or comment on its development.
The KDE Frameworks are also released under the permissive LGPL or BSD/MIT licenses, making them ideal and usable for any type of software.
Organization
Each of the KDE Frameworks has a Tier and a Type, as you will see in the API documentation. While not critical to using the frameworks, this organization can help developers in determining the frameworks' dependencies.
Tiers group the frameworks according to what they link to during compilation.
- Tier 1 Frameworks can depend only on Qt official frameworks or other system libraries;
- Tier 2 Frameworks can depend only on Tier 1 Frameworks, Qt official frameworks, or other system libraries;
- Tier 3 Frameworks can depend only on other Tier 3 Frameworks, Tier 2 Frameworks, Tier 1 Frameworks, Qt official frameworks, or other system libraries.
Types, on the other hand, refer to the framework's runtime dependencies:
- Functional Frameworks cannot have runtime dependencies. KArchive, for example, can be used as-is as a drop-in library.
- Integration Frameworks can have optional runtime dependencies and aim at integrating with the underlying OS/Platform. Solid needs other runtime components to deliver hardware information on different platforms.
- Solutions have mandatory runtime dependencies to function. KIO, the KDE I/O framework, requires certain daemons to offer a network-transparent virtual filesystem.
Quick Start Guide
How easy is it to use KDE Frameworks 5? Just as easy as using any Qt widget or adding any C++ library to your project. You don't even have to switch away from QMake if that's your cup of tea. Here's one very quick and dirty example of how simple it is to use a framework.
Step 1: Install the Framework you need
For this example, we'll be using the KDatePicker widget from the KWidgetsAddons framework. On KDE Neon/Ubuntu/Debian, it's as simple as:
sudo apt install libkf5widgetsaddons-dev
Adjust according to your Linux distro's packaging system, of course. If you want the latest version of the framework and it isn't available from your distro, you will have to get it from the source (Git or tarball) and build it yourself. Check out the KDE Community's handy guide to building KDE software from source.
Step 2: Add the Framework to your Project
Add the Framework's name, properly capitalized, in your QMake project file just like you would any other Qt module.
TEMPLATE = app
TARGET = kdatepicker-example
QT += core widgets KWidgetsAddons
SOURCES += main.cpp
If you're already using CMake as your build system of choice, you'll want to also grab the Extra CMake Modules made by the KDE community to provide modules and macros to make finding and linking to Frameworks so much easier.
Step 3: Use the Framework
KDatePicker, like many other widgets from KDE Frameworks, behave just like any Qt widget. As such, you can simply slot them in or use them in Qt projects with no problem at all. Here is a contrived example where selecting a date from the calendar widget displays its string representation on the label beside it.
#include <KDatePicker>
#include <QApplication>
#include <QLabel>
#include <QHBoxLayout>
int main(int argc, char* argv[])
{
QApplication app(argc, argv);
QWidget* window = new QWidget;
QLabel* dateLabel = new QLabel(QDate::currentDate().toString());
KDatePicker* datePicker = new KDatePicker;
QObject::connect(datePicker, &KDatePicker::dateSelected, [=] (const QDate &dateSelected) { dateLabel->setText(dateSelected.toString()); });
QHBoxLayout* layout = new QHBoxLayout;
layout->addWidget(dateLabel);
layout->addWidget(datePicker);
window->setLayout(layout);
window->show();
return app.exec();
}Just build the project as normal and that's it! Welcome to the wonderful world of KDE-powered software!
Frameworks Sampler
Now that you've seen how easy it is to add KDE Frameworks into your software, here's an appetizer of the various frameworks available and what they can do for you.
- Like KDatePicker above, KWidgetsAddons offers a wide variety of add-on widgets that go beyond what Qt itself offers. On the other hand, KCoreAddons includes non-graphical utility classes that help manage children processes, create autosave files, and create factory-style plugins.
- Sonnet adds multi-language spellchecking to any QTextEdit (really QTextDocument) object with support for different spelling backends while KSyntaxHighighting extends Qt's syntax highlighting support with a standardized and expandable syntax definition format.
- ThreadWeaver takes the pain out of one of the most difficult aspects of modern application development: multi-threaded programming.
- KConfig lets you have a configuration system that works across platforms, no matter the actual back-end file format. KPackage, on the other hand, can help you extend your programs with content that is installed like plugins.
- If you need to embed an advanced text editor but don't want to go through the hassle of writing one yourself, KTextEditor offers all the functionality you need either as a library or an embeddable KPart.
- Kirigami is like a framework inside a framework, providing a rich set of Qt Quick components for developing a new breed of applications that bridge the divide between screen sizes and form factors.
- And, of course, there's the Plasma framework that serves as the foundation for KDE's Plasma workspaces, both for desktops as well as mobile, giving developers the building blocks for creating primary user interfaces as well as applets (widgets) to run on those workspaces.
Be sure to check the full collection of 80 KDE Frameworks on the API documentation website along with other KDE libraries you can use to develop the next killer app, be it on Linux or Windows, desktop or mobile, and anything else in between.