qtquick-how-tos.qdoc

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// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \page qtquick-how-tos.html
    \title Qt Quick How-tos
 
    This page aims to provide an easily discoverable, useful reference that
    shows the simplest and best way of performing specific tasks in Qt Quick.
    Each solution provides QML and/or C++ code snippets where applicable, and
    every snippet is automatically tested by Qt to ensure they remain
    functional.
 
    How do I:
 
    \list
    \li \l {Call a C++ function from QML when a Button is clicked}
    \li \l {See which item has active focus}
    \li \l {Create a time picker like Android's TimePickerDialog}
    \li \l {Use a C++ enum in JavaScript}
    \endlist
 
 
    \section1 Call a C++ function from QML when a Button is clicked
 
    Assuming that the C++ type should be globally available to the QML
    files in the application, the simplest way is to make it a QML singleton
    with \l QML_SINGLETON. For example, in the header file, \c backend.h:
 
    \snippet how-tos/how-to-cpp-button/backend.h file
 
    \c backend.cpp:
 
    \snippet how-tos/how-to-cpp-button/backend.cpp file
 
    You can then call that function from any QML file:
 
    \snippet how-tos/how-to-cpp-button/Main.qml file
 
    If the C++ type only needs to be available to a small set of QML files,
    consider using \l QML_ELEMENT. For more ways of exposing C++ types to QML,
    see \l {Choosing the Correct Integration Method Between C++ and QML}.
 
    This example assumes that the \c Backend type is available in a QML module.
    With CMake, this is done via \l qt_add_qml_module. For an example that
    demonstrates this in detail, see \l {Building a QML application}.
 
 
    \section1 See which item has active focus
 
    Write a \l {Property change signal handlers}{property change signal handler}
    for the window's \l {Window::}{activeFocusItem} property:
 
    \snippet how-tos/how-to-qml/active-focus-debugging/ActiveFocusDebuggingMain.qml file
 
    This will print the item which currently has active focus to the console.
    To ensure that the output is useful, give each item a descriptive
    \l {QtObject::}{objectName}.
 
 
    \section1 Create a time picker like Android's TimePickerDialog
 
    We've prepared an example that consists of a few
    \l {https://code.qt.io/cgit/qt/qtdeclarative.git/tree/tests/auto/quick/doc/how-tos/how-to-qml/time-picker/TimeComponentLabel.qml?h=\QtMajorVersion.\QtMinorVersion}
    {QML files} which demonstrate how to do this. They can be used
    in your application in the following manner:
 
    \snippet how-tos/how-to-qml/time-picker/TimePickerMain.qml file
 
    \table
        \row
            \li \image how-to-time-picker-light.png
                \caption TimePickerDialog in its light theme.
            \li \image how-to-time-picker-dark.png
                \caption TimePickerDialog in its dark theme.
    \endtable
 
 
    \section1 Use a C++ enum in JavaScript
 
    To expose a C++ enum to JavaScript (that is, \l QJSEngine, not
    \l QQmlEngine or \l QQmlApplicationEngine), use
    \l QJSEngine::newQMetaObject():
 
    \quotefromfile how-tos/how-to-cpp-enum-js/tst_how-to-cpp-enum-js.cpp
    \skipto QJSEngine engine
    \printuntil setProperty
    \skipto Backend backend
    \printuntil backend.load()
 
    The enum can then be used from JavaScript:
 
    \snippet how-tos/how-to-cpp-enum-js/script.mjs file
 
    When using \l QQmlEngine or \l QQmlApplicationEngine, there are easier
    options; see
    \l {Choosing the Correct Integration Method Between C++ and QML}
    for more information.
 
    \c backend.h:
 
    \snippet how-tos/how-to-cpp-enum-js/backend.h file
 
    \c backend.cpp:
 
    \snippet how-tos/how-to-cpp-enum-js/backend.cpp file
 
    For more information, see \l {QObject Integration}.
*/