In this chapter, you will learn the following topics:

• A brief overview of Qt
• The Qt Framework
• Installing Qt on Ubuntu
• Developing Qt Core application
• Developing a Qt GUI application
• Using layouts in the Qt GUI application
• Understanding signals and slots for event handling
• Using multiple layouts in the Qt application

Qt is a cross-platform application framework developed in C++. It is supported on various platforms, including Windows, Linux, Mac OS, Android, iOS, Embedded Linux, QNX, VxWorks, Windows CE/RT, Integrity, Wayland, X11, Embedded Devices, and so on. It is primarily used as a human-machine-interface (HMI) or Graphical User Interface (GUI) framework; however, it is also used to develop a command-line interface (CLI) applications. The correct way of pronouncing Qt is cute. The Qt application framework comes in two flavors: open source and with a commercial license.

Qt is the brainchild of Haavard Nord and Eirik Chambe-Eng, the original developers, who developed it back in the year 1991.

As C++ language doesn't support GUI natively, you must have guessed that there is no event management support in C++ language out of the box. Hence, there was a need for Qt to support its own event handling mechanism, which led to the signals and slots technique. Under the hood, signals and slots use the observer design pattern that allows Qt objects to talk to each other. Does this sound too hard to understand? No worries! Signals are nothing but events, such as a button click or window close, and slots are event handlers that can supply a response to these events in the way you wish to respond to them.

To make our life easier in terms of Qt application development, Qt supports various macros and Qt-specific keywords. As these keywords will not be understood by C++, Qt has to translate them and the macros into pure C++ code so that the C++ compiler can do its job as usual. To make this happen in a smoother fashion, Qt supports something called Meta-Object Compiler, also known as moc.

Qt is a natural choice for C++ projects as it is out-and-out C++ code; hence, as a C++ developer, you will feel at home when you use Qt in your application. A typical application will have both complex logic and impressive UI. In small product teams, typically one developer does multiple stuff, which is good and bad.

Generally, professional developers have good problem-solving skills. Problem-solving skills are essential to solve a complex problem in an optimal fashion with a good choice of data structures and algorithms.

Developing an impressive UI requires creative design skills. While there are a countable number of developers who are either good at problem-solving or creative UI design, not all developers are good at both. This is where Qt stands out.

Say a start-up wants to develop an application for their internal purposes. For this, a simple GUI application would suffice, where a decent looking HMI/GUI might work for the team as the application is meant for internal purposes only. In such scenarios, the entire application can be developed in C++ and the Qt Widgets framework. The only prerequisite is that the development team must be proficient in C++.

However, in cases where a mobile app has to be developed, an impressive HMI becomes mandatory. Again, the mobile app can be developed with C++ and Qt Widgets. But now there are two parts to this choice. The good part is that the mobile app team has to be good at just C++. The bad part of this choice is that there is no guarantee that all good C++ developers will be good at designing a mobile app's HMI/GUI.

Let's assume the team has one or two dedicated Photoshop professionals who are good at creating catchy images that can be used in the GUI and one or two UI designers who can make an impressive HMI/GUI with the images created by the Photoshop experts. Typically, UI designers are good at frontend technologies, such as JavaScript, HTML, and CSS. Complex business logic can be developed in the powerful Qt Framework, while the HMI/GUI can be developed in QML.

QML is a declarative scripting language that comes along with the Qt application framework. It is close to JavaScript and has Qt-specific extensions. It is good for rapid application development and allows UI designers to focus on HMI/GUI and C++ developers to focus on the complex business logic that can be developed in Qt Framework.

Since both the C++ Qt Framework and QML are part of the same Qt application framework, they go hand in hand seamlessly.

Qt is a vast and powerful framework; hence this chapter will focus on the basic essentials of Qt to get you started with Qt. If you are curious to learn more, you may want to check out my other upcoming book that I'm working on, namely Mastering Qt and QML Programming.