Transitioning from Qt 5 to Qt 6

In this chapter, we will learn about the changes that have been made in Qt 6 and how you can upgrade your existing Qt 5 project to Qt 6. Unlike previous updates, Qt 6 is almost a complete rewrite of the entire Qt code base from the ground up, including all the underlying classes. Such major changes may break your existing Qt 5 project if you simply switch over to Qt 6.

In this chapter, we’re going to cover the following main topics:

• Changes in C++ classes
• Using Clazy checks for Clang and C++
• Changes in QML types

Technical requirements

The technical requirements for this chapter include Qt 6.6.1 MinGW 64-bit, Qt 5.15.2 MinGW 64-bit, and Qt Creator 12.0.2. All the code used in this chapter can be downloaded from the following GitHub repository: https://github.com/PacktPublishing/QT6-C-GUI-Programming-Cookbook---Third-Edition-/tree/main/Chapter06.

Changes in C++ classes

In this recipe, we will learn what the changes in Qt6’s C++ classes are.

How to do it…

Follow these steps to learn about C++ classes in Qt6:

1. Create a new Qt Console Application by going to File | New Project.
2. We will open up the main.cpp file and add the following headers:

   #include <QCoreApplication>
   #include <QDebug>
   #include <QLinkedList>
   #include <QRegExp>
   #include <QStringView>
   #include <QTextCodec>
   #include <QTextEncoder>
   #include <QTextDecoder>

3. After that, add the following code for demonstrating the QLinkedList class:

   int main(int argc, char *argv[])
   {
       QCoreApplication a(argc, argv);
       // QLinkedList
       QLinkedList<QString> list;
       list << "string1" << "string2" << "string3";
       QLinkedList<QString>::iterator...

Using Clazy checks for Clang and C++

In this chapter, we will learn how to use the Clazy checks from the Clang toolset to automatically display warnings when obsolete Qt 5 classes and functions are detected in your Qt project.

How to do it…

Let’s get started by following these steps:

1. We will use the same project from the preceding example. Then, proceed to open up the preferences window by going to Edit | Preferences….
2. After that, go to the Analyzer page and click on the button beside Diagnostic configuration:

Figure 6.1 – Open up the Diagnostic configuration window

3. Select the Default Clang-Tidy and Clazy checks option at the top and click the Copy… button, as shown in Figure 6.2. Give it a name and click OK. The new option will now appear under the Custom category:

Figure 6.2 - Click on the Copy button

4. Then, open the Clazy Checks tab, enable the following...

Changes in QML types

In this chapter, we will learn what changes have been made in Qt 6 compared to Qt 5.

How to do it…

Let’s get started by following these steps:

1. Create a new Qt Quick Application by going to File | New Project.
2. Select the Qt 6.2 option for Minimum required Qt version when defining project details.

Figure 6.5 – Select Qt 6.2 as Minimum required Qt version

3. Once you have created the project, open up main.qml and add these properties to the file:

   import QtQuick
   Window {
       width: 640
       height: 480
       visible: true
       title: qsTr("Hello World")
       property variant myColor: "red"
       property url imageFolder: "/images"

4. Next, add a Rectangle object to main.qml, as shown in the following:

   Rectangle {
       id: rect
    ...