You will use different components depending on whether you are developing an application or Plasma, and the nature of your application. The HIG interaction patterns apply regardless of the components you use.
Qt offers two ways of defining the application user interface (UI). Which one to choose depends on the nature of your application. The application logic is written in C++ (or other supported languages) regardless of the kind of application created.
Qt Widgets is the traditional way of writing Qt applications. It is best suited for traditional desktop applications with complex interfaces, e.g. KDevelop.
QML/QtQuick is the modern way of developing Qt applications. It features a declarative approach to writing touch and mobile friendly UIs with fluent gestures. QML/QtQuick is best suited for mobile and convergent applications.
Kirigami builds on top of QtQuick and helps you write convergent applications. It features controls that adapt their presentation according to the device's form factor.
To test qml scenes use
Plasma is built using widgets (also called Plasmoids), allowing you to move, mix, add, and remove to fit the user's workflow. Some widgets are built using Plasma Components 3, which are based on Qt Quick Controls 2.
The KDE HIG defines a set of common components independent of any device type.
Workspace: The top-level container of the whole user interface. Often called "desktop", "home screen", or "shell", it shows the wallpaper and allows users to add widgets, app launchers, files and folders.
Application Launcher: Provides an overview of installed applications and allows the user to launch applications.
Application Shortcuts: Provides quick access to frequently-used applications.
Active Application Overview: Gives the user a window arrangement for active applications allowing the user to search, select, and close said application.
Workspace Tools: Provides quick access to functionality integrated into the workspace that is both highly visible to the user and frequently changed. For example, enabling/disabling WiFi, or Bluetooth, or show notifications.
Application-Workspace Interaction: Displays information about each application's windows, and provides ways to move or close them and change how they run within the workspace.
Application: The top-level container of a single application.
Application Tools: Provides access to an application's commonly-used functionality in an always-accessible toolbar or menubar. These tools should not change based on what the application shows.
Application Content: The actual content of an application. This depends on the application itself, but conformance to the KDE HIG should make it easier to allow convergence for this component. This part of the application can also contain contextually-appropriate tools that operate directly on the active or selected content.
There are three different kinds of themes influencing the the look-and-feel of KDE applications and the Plasma workspace.
- Window decoration
The default for all three is the Breeze theme.