Qt6/Example-Guideline

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

See also: Documentation Style for Examples.

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.
• Ensure the example is included in the related examples-manifest.xml file and shown part of documentation. See https://doc.qt.io/qt-6/26-qdoc-configuration-example-manifest-files.html
  • If the example is not shown, consider moving it under tests/manual/examples.
  • Do not add examples to the examples-manifest.xml file that don't meet this guideline criteria.

Formatting

RECOMMENDED

• C++: Use clang-format for C++ files
• QML: Use qmlformat -i -n to normalize formatting and order of QML files

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.
• Place .qml and .js files in the same directory as the qt_add_qml_module. Otherwise their implicit import is not the module they belong to.

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

• Prefer making signal/slot connections using functor syntax over the string-based versions: https://doc.qt.io/qt-6/signalsandslots.html
  • For short (~5 lines of code) slots, consider using signal/slot connection with lambdas
  • Longer slot should be member functions

Naming the example

• 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 using the

  \examplecategory
  

  macro, for example:

 \example My Graphical Application
 \examplecategory {Graphics}

This will end up as

 <meta> 
   <entry name="category">Graphics</entry> 
 </meta>

in the <example> section of the relevant examples-manifest.xml file.

• Example should typically 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
  • Larger examples which look modern
• Desktop
  • Typical traditional UI used with mouse
• Mobile
  • Touch UI that adapts to different screen sizes
• Embedded
  • One screen size touch based UI
• Graphics & Multimedia
  • Quick3D, Charts, Multimedia, etc.
• Data Visualization & 3D
  • Qt Data Visualization, Qt 3D, Qt Quick 3D
• Data Processing & I/O
  • XML, IO Device, etc.
• Connectivity
  • Bluetooth, IPC, MQTT, etc.
• Networking
  • HTTP, TCP, and UDP
• Positioning & Location
• Web Technologies
  • WebEngine, WebView, WebChannel

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.

Example metadata

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 tag {quick,network}

Highlighting

In Qt Creator, examples inside a category are shown in alphabetical order . One can 'highlight' examples though, so that they are shown first. We should aim for highlighting 5-12 examples per category.

To mark an example as highlighted, you add it's name, prefixed with a module name and a slash to manifestmeta.highlighted.names of the respective .qdocconf file:

  manifestmeta.highlighted.names = "QtDoc/Calqlatr" \
                                   "QtDoc/Coffee Machine" \
                                   "QtDoc/Dice"

Simple wildcard matching is supported; by using * at the end it's possible to match multiple examples with a single string.

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.
• Image assets should have the minimum size rquired. See for instance Optimizing Images for advice.

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 the 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

You should be able to build each example, if its CMakeLists.txt and .pro files are correctly configured, using either of them. This should be possible using a standard build (with -no-make examples), building from the example's source in a git checkout (handy for verifying your improvements). With your build's qtbase/bin/ in your PATH, for cmake and qt-cmake, first cd to the directory in which you want the build artefacts.

With CMake

qt-cmake path/to/example/dir/ && cmake --build . --parallel

With QMake

qmake path/example/dir/whatever.pro && make

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. These macros are exclusively to support "namespaced" builds of Qt (https://wiki.qt.io/Qt_In_Namespace) and surround declarations of types from the Qt libraries and overloads of operators that are not found by argument-dependent name lookup. If using the macros is considered too ugly, another option is to #include the respective Qt header.

• Verify if the example was ported to the Qt for Python project and if exists, notify the team with a comment on https://bugreports.qt.io/browse/PYSIDE-2206 with a link to the review of your changes.