Qt: a framework for writing graphic applications in C++, also Python

Installing Qt on Ubuntu

You need to install packages:

sudo apt install -y qtcreator qtbase5-dev qt5-qmake cmake

Recommended: cmake-doc

Warning These packages would take up about 1GB space on your hard disk.

The model/view architecture

Model-View-Controller (MVC) is a design pattern originating from Smalltalk that is often used when building user interfaces. In Design Patterns, Gamma et al. write:

MVC consists of three kinds of objects. The Model is the application object, the View is its screen presentation, and the Controller defines the way the user interface reacts to user input. Before MVC, user interface designs tended to lump these objects together. MVC decouples them to increase flexibility and reuse.

If the view and the controller objects are combined, the result is the model/view architecture. This still separates the way that data is stored from the way that it is presented to the user, but provides a simpler framework based on the same principles. This separation makes it possible to display the same data in several different views, and to implement new types of views, without changing the underlying data structures. To allow flexible handling of user input, we introduce the concept of the delegate. The advantage of having a delegate in this framework is that it allows the way items of data are rendered and edited to be customized.

The model communicates with a source of data, providing an interface for the other components in the architecture. The nature of the communication depends on the type of data source, and the way the model is implemented.

The view obtains model indexes from the model; these are references to items of data. By supplying model indexes to the model, the view can retrieve items of data from the data source.

In standard views, a delegate renders the items of data. When an item is edited, the delegate communicates with the model directly using model indexes.

Generally, the model/view classes can be separated into the three groups described above: models, views, and delegates. Each of these components is defined by abstract classes that provide common interfaces and, in some cases, default implementations of features. Abstract classes are meant to be subclassed in order to provide the full set of functionality expected by other components; this also allows specialized components to be written.

Models, views, and delegates communicate with each other using signals and slots:

• Signals from the model inform the view about changes to the data held by the data source.
• Signals from the view provide information about the user's interaction with the items being displayed.
• Signals from the delegate are used during editing to tell the model and view about the state of the editor.

Model/View Tutorial

(From https://doc.qt.io/qt-6/modelview.html)

Table, list and tree widgets are components frequently used in GUIs. There are 2 different ways how these widgets can access their data. The traditional way involves widgets which include internal containers for storing data. This approach is very intuitive, however, in many non-trivial applications, it leads to data synchronization issues. The second approach is model/view programming, in which widgets do not maintain internal data containers. They access external data through a standardized interface and therefore avoid data duplication. This may seem complicated at first, but once you take a closer look, it is not only easy to grasp, but the many benefits of model/view programming also become clearer.

Building UIs with Qt Quick

Qt Quick is for creating dynamic and fluid user interfaces. The Qt Quick Controls module supplies QML types such as buttons, dialogs, and menus. You can use QML, a declarative language, to build the UI and JavaScript to implement the logic.

Qt Widgets User Interfaces

Qt Widgets are the user interface elements that are typical in desktop environments. The widgets integrate well to the underlying platform providing native look and feel on Windows, Linux and macOS. The widgets are mature and feature rich user interface elements suitable for mostly traditional user interfaces. In contrast to Qt Quick, the widgets are for creating large desktop applications and less suited for creating touch-centric applications with fluid interfaces.