Qt6/Example-Guideline

When creating or updating Qt examples, developer should consider the best practises and guidelines listed in this document.

Evaluate if the example is meaningful or should it be removed/merged

MANDATORY

• Check if there are similar examples for the same topic and consider if both are really needed or should they be merged.
• Check also documentation on the topic and if that includes inline code snippet that would be adequate instead of complete example.

No C++ or qml warnings

MANDATORY

• Example's C++ code should be by minimum compiled with the same compiler warning flags as Qt.
• Use qmllint for qml code: https://doc-snapshots.qt.io/qt6-dev/qtquick-tool-qmllint.html
• Enable compiler warnings and check if the reported issues are fixable with meaningful effort.

RECOMMENDED
Consider also compiling with the more strict warning flags and fix possible issues they reveal especially if these are in the example code.

GCC

Use -Wall and consider -Wextra parameter: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Clang

Use -Weverything compiler parameter: https://clang.llvm.org/docs/UsersManual.html#diagnostics-enable-everything

Visual Studio

Use /Wall compiler parameter: https://docs.microsoft.com/en-us/cpp/build/reference/compiler-option-warning-level

Qt6 best practises and changes

MANDATORY

• Check the porting guide for Qt6: https://doc.qt.io/qt-6/portingguide.html
• Ensure the example complies with the Qt 6 porting guides for each module the example is using: https://doc.qt.io/qt-6/modulechanges.html
• Check the best practises for QtQML & QtQuick: https://doc-snapshots.qt.io/qt6-dev/qtquick-bestpractices.html
• Do not use versions in QML import statements. This is usally a left-over from Qt 5.

Leveraging C++17

MANDATORY

• Follow Qt Coding conventions: https://wiki.qt.io/Coding_Conventions
• Use clazy plugin (comes also with Qt Creator): https://www.qt.io/blog/porting-from-qt-5-to-qt-6-using-clazy-checks

RECOMMENDED

• Consider using signal/slot connection with lambdas: https://doc.qt.io/qt-6/signalsandslots.html
  • Keep lambdas short and to the point
  • Don't use unnamed lambdas

Naming the example, categorisation and adding tags

MANDATORY

Naming

• Don't add the Qt module name or the word "Example" to the example name. e.g. QtWidgets Application Example → Text editor application
  • Exception: If it's really not possible to clearly describe the example's functionality without using (part of) the module name, that can still be done (e.g. "Simple CoAP Client Example" from the Qt CoAP module).

Categorisation

• Add example application to a suitable category, for example:

 \example My Example 
 \meta category {Graphics}

This will end up as

 <categories> 
   <category>Graphics</category> 
 </categories>

in the <example> section of the relevant examples-manifest.xml file.
For further details see: https://codereview.qt-project.org/c/qt/qttools/+/447246

• Example should belong to only one category. Consider what's the most essential feature that the example is teaching and pick the category accordingly.
  • If there isn't an appropriate category for the example, it can be left out. Such examples will be listed under category 'Other'.
  • In the description and tags (see below) you can add more information to make finding the example easy.

Acceptable categories

• Application Examples
• Connectivity
• Graphics
• Input/Output
• Networking
• User Interfaces
• Internationalization
• Desktop
• Mobile
• Embedded
• Positioning & Location

RECOMMENDED

• Confirm that the example shows up in Qt Creator's Welcome screen.
• Check that the example description text shown in Creator contains the right keywords for users to find it.
• Add appropriate tags to the example; see below.

Tags

• Tags are used to set additional keywords for the example.
• This makes it easier to find them by searching in Qt Creator's example view
• Common tags are for the UI stack (widgets, quick), and the 'main' module of the example.
  • Note that QDoc automatically adds tags for the Qt module, if not already set manually.
• Don't add, as tags, information which is already part of the category, example name or description.
• Don't add platform information in the tags

Example:

 \example My Example
 \meta tags {quick,network}

Visual Style

MANDATORY

• Screen shots taken with high dpi resolution, minimum image size 440x320.
  • Note: Images can be larger but should follow either 4:3 or 5:4 aspect ratio. Take meaningful image that gives an idea what the example is about.
• Icons should be suitable for high dpi screen with minimum size of 64x64.

RECOMMENDED

• Consider using Qt Quick over Qt Widgets but remember also dependency restrictions with module api examples.
• Create example's qml part to be compatible with Qt Design Studio.
  • Define purely declarative qml files with .ui.qml file extension.
  • Test the project also in Qt Design Studio.
• Layouts should be tested on multiple platforms (macOS, Linux, Windows, iOS, Android, Embedded Linux / EGLFS) with full HD target screen resolution.

Build System

MANDATORY

• Our users should be able to build with both qmake and CMake. Both build systems should therefore work.
• Check that the example runs without any issues when opened in Qt Creator welcome screen, on all platforms. If additional steps are necessary, or examples only run on some platforms, make sure that is is prominently stated in the example's documentation.
• CMake
  • Do not use the 'find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)' pattern that is created for instance in CMakeLists.txt files created by Qt Creator wizards. This pattern is for keeping compatibility with Qt 5, which we don't strive for with Qt 6 examples.
  • Use qt_standard_project_setup() instead enabling AUTOMOC, AUTOUIC manually
  • Use PRIVATE linkage

RECOMMENDED

• Avoid including (re)sources from outside the example directory, as examples should be self-contained.

Enable automated release testing

RECOMMENDED
For enabling RTA testing add unique object names for all the UI objects

• https://doc.qt.io/qt-6/qobject.html#setObjectName
• https://kb.froglogic.com/squish/howto/explicitly-naming-objects/

Misc

MANDATORY

• Do not use QT_BEGIN_NAMESPACE ... QT_END_NAMESPACE for example types. This namespace is exclusively for types in the Qt libraries.