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How to create QML singleton

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  • K KejPi

    I do not know how to attach file, so this is cope and paste of minimal example:

    CMakeList.txt

    cmake_minimum_required(VERSION 3.16)

project(SingletonTest VERSION 0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.4 REQUIRED COMPONENTS Quick)

qt_standard_project_setup()

qt_add_executable(appSingletonTest
    main.cpp
)

set_source_files_properties(qml/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qml/main.qml
    QML_FILES qml/Colors.qml
)

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
set_target_properties(appSingletonTest PROPERTIES
#    MACOSX_BUNDLE_GUI_IDENTIFIER com.example.appSingletonTest
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(appSingletonTest
    PRIVATE Qt6::Quick
)

include(GNUInstallDirs)
install(TARGETS appSingletonTest
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

    main.cpp:

    #include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(u"qrc:/SingletonTest/qml/main.qml"_qs);
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

    qml/main.qml:

    import QtQuick
import SingletonTest

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Rectangle {
        width: parent.width/2
        height: parent.height/2
        anchors.centerIn: parent
        color: Colors.myColor
    }
}

    qml/Colors.qml:

    pragma Singleton
import QtQuick

QtObject {
    id: colors
    readonly property color myColor: "red"
}

    When I run it I get this message:

    qrc:/SingletonTest/qml/main.qml:14: TypeError: Colors was a singleton at compile time, but is not a singleton anymore.
    GrecKoG Offline
    GrecKoG Offline
    GrecKo
    Qt Champions 2018
    wrote on last edited by
    #5

    What if you put the QML files in the root folder of the project? Colors.qml instead of qml/Colors.qml

    Also I'd remove the second QML_FILES in qt_add_qml_module

    K 1 Reply Last reply
    0
    • GrecKoG GrecKo

      What if you put the QML files in the root folder of the project? Colors.qml instead of qml/Colors.qml

      Also I'd remove the second QML_FILES in qt_add_qml_module

      K Offline
      K Offline
      KejPi
      wrote on last edited by
      #6

      If I move Colors.qml to root folder and change CMakeList.txt accordingly:

      set_source_files_properties(Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qml/main.qml
              Colors.qml
)

      I get this error when I run the application:

      qrc:/SingletonTest/qml/main.qml:14: ReferenceError: Colors is not defined
      K 1 Reply Last reply
      0
      • K KejPi

        If I move Colors.qml to root folder and change CMakeList.txt accordingly:

        set_source_files_properties(Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qml/main.qml
              Colors.qml
)

        I get this error when I run the application:

        qrc:/SingletonTest/qml/main.qml:14: ReferenceError: Colors is not defined
        K Offline
        K Offline
        KejPi
        wrote on last edited by KejPi
        #7

        It seems all QML files must be in root folder including some other custom components files.

        If I do this, it works:

        set_source_files_properties(Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES main.qml
              Colors.qml
              SomeComponent.qml
)

        This strange, so far I put all my QML files to dedicated folder (qml/) to separate it from C++ and everything was working (see my first example code) - only the singleton causes some problem.

        I could consider this as workaround but I do not like it since I will mix QML with C++ and it will be a mess :-(

        EDIT: It seems that this construction works too:

        set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
set_source_files_properties(qmlfiles/main.qml PROPERTIES QT_RESOURCE_ALIAS main.qml)
set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_RESOURCE_ALIAS Colors.qml)
set_source_files_properties(qmlfiles/SomeComponent.qml PROPERTIES QT_RESOURCE_ALIAS SomeComponent.qml)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qmlfiles/main.qml
              qmlfiles/Colors.qml
              qmlfiles/SomeComponent.qml
)
        ekkescornerE J 2 Replies Last reply
        0
        • K KejPi

          It seems all QML files must be in root folder including some other custom components files.

          If I do this, it works:

          set_source_files_properties(Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES main.qml
              Colors.qml
              SomeComponent.qml
)

          This strange, so far I put all my QML files to dedicated folder (qml/) to separate it from C++ and everything was working (see my first example code) - only the singleton causes some problem.

          I could consider this as workaround but I do not like it since I will mix QML with C++ and it will be a mess :-(

          EDIT: It seems that this construction works too:

          set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
set_source_files_properties(qmlfiles/main.qml PROPERTIES QT_RESOURCE_ALIAS main.qml)
set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_RESOURCE_ALIAS Colors.qml)
set_source_files_properties(qmlfiles/SomeComponent.qml PROPERTIES QT_RESOURCE_ALIAS SomeComponent.qml)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qmlfiles/main.qml
              qmlfiles/Colors.qml
              qmlfiles/SomeComponent.qml
)
          ekkescornerE Offline
          ekkescornerE Offline
          ekkescorner
          Qt Champions 2016
          wrote on last edited by
          #8

          @KejPi open a bugreport because QML SINGLETON doesn't work if not in root folder

          ekke ... Qt Champion 2016 | 2024 ... mobile business apps
          5.15 --> 6.9 https://t1p.de/ekkeChecklist
          QMake --> CMake https://t1p.de/ekkeCMakeMobileApps

          MesrineM 1 Reply Last reply
          0
          • ekkescornerE ekkescorner

            @KejPi open a bugreport because QML SINGLETON doesn't work if not in root folder

            MesrineM Offline
            MesrineM Offline
            Mesrine
            wrote on last edited by
            #9

            @ekkescorner

            I do not know why the one from the post does not work, but singletons from subdirectories work.

            I used here

            ekkescornerE K 2 Replies Last reply
            0
            • MesrineM Mesrine

              @ekkescorner

              I do not know why the one from the post does not work, but singletons from subdirectories work.

              I used here

              ekkescornerE Offline
              ekkescornerE Offline
              ekkescorner
              Qt Champions 2016
              wrote on last edited by
              #10

              @Mesrine aaah - good to know. just porting my apps from QMake to CMake. next step will be to modernize my apps, where I'll need QML SINGLETONS, too

              ekke ... Qt Champion 2016 | 2024 ... mobile business apps
              5.15 --> 6.9 https://t1p.de/ekkeChecklist
              QMake --> CMake https://t1p.de/ekkeCMakeMobileApps

              1 Reply Last reply
              0
              • K KejPi

                It seems all QML files must be in root folder including some other custom components files.

                If I do this, it works:

                set_source_files_properties(Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES main.qml
              Colors.qml
              SomeComponent.qml
)

                This strange, so far I put all my QML files to dedicated folder (qml/) to separate it from C++ and everything was working (see my first example code) - only the singleton causes some problem.

                I could consider this as workaround but I do not like it since I will mix QML with C++ and it will be a mess :-(

                EDIT: It seems that this construction works too:

                set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
set_source_files_properties(qmlfiles/main.qml PROPERTIES QT_RESOURCE_ALIAS main.qml)
set_source_files_properties(qmlfiles/Colors.qml PROPERTIES QT_RESOURCE_ALIAS Colors.qml)
set_source_files_properties(qmlfiles/SomeComponent.qml PROPERTIES QT_RESOURCE_ALIAS SomeComponent.qml)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qmlfiles/main.qml
              qmlfiles/Colors.qml
              qmlfiles/SomeComponent.qml
)
                J Offline
                J Offline
                Janson
                wrote on last edited by Janson
                #11
                This post is deleted!
                1 Reply Last reply
                0
                • K Offline
                  K Offline
                  KejPi
                  wrote on last edited by
                  #12

                  I have a small example project that clearly shows it does not work as expected. I can share it but I do not know how to do it here. Maybe I did something wrong - I have juste created project in QtCreator and moved all QML files in subdirectory.

                  1 Reply Last reply
                  0
                  • MesrineM Mesrine

                    @ekkescorner

                    I do not know why the one from the post does not work, but singletons from subdirectories work.

                    I used here

                    K Offline
                    K Offline
                    KejPi
                    wrote on last edited by
                    #13

                    @Mesrine Could it be that you only have singleton in the module while I have all my QML files there?

                    1 Reply Last reply
                    0
                    • K KejPi

                      I do not know how to attach file, so this is cope and paste of minimal example:

                      CMakeList.txt

                      cmake_minimum_required(VERSION 3.16)

project(SingletonTest VERSION 0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.4 REQUIRED COMPONENTS Quick)

qt_standard_project_setup()

qt_add_executable(appSingletonTest
    main.cpp
)

set_source_files_properties(qml/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)
qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES qml/main.qml
    QML_FILES qml/Colors.qml
)

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
set_target_properties(appSingletonTest PROPERTIES
#    MACOSX_BUNDLE_GUI_IDENTIFIER com.example.appSingletonTest
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(appSingletonTest
    PRIVATE Qt6::Quick
)

include(GNUInstallDirs)
install(TARGETS appSingletonTest
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

                      main.cpp:

                      #include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    const QUrl url(u"qrc:/SingletonTest/qml/main.qml"_qs);
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

                      qml/main.qml:

                      import QtQuick
import SingletonTest

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Rectangle {
        width: parent.width/2
        height: parent.height/2
        anchors.centerIn: parent
        color: Colors.myColor
    }
}

                      qml/Colors.qml:

                      pragma Singleton
import QtQuick

QtObject {
    id: colors
    readonly property color myColor: "red"
}

                      When I run it I get this message:

                      qrc:/SingletonTest/qml/main.qml:14: TypeError: Colors was a singleton at compile time, but is not a singleton anymore.
                      MesrineM Offline
                      MesrineM Offline
                      Mesrine
                      wrote on last edited by Mesrine
                      #14

                      @KejPi

                      I have used your minimal example and works ok :) .

                      The only thing I changed was that instead of CMakeList.txt i named CMakeLists.txt.

                      I have tested it with qt(shared libraries) 6.5,6.6,6.7 in Linux.

                      Make sure you are using the correct CMakeLists.txt.
                      And let us know your platform and Qt version.

                      1 Reply Last reply
                      0
                      • K Offline
                        K Offline
                        KejPi
                        wrote on last edited by KejPi
                        #15

                        Yes, it was only typo, I use the CMakeLists.txt created by Qt Creator.
                        I am running it on MacOS 14.2, Qt version 6.5.3

                        MesrineM 1 Reply Last reply
                        0
                        • K KejPi

                          Yes, it was only typo, I use the CMakeLists.txt created by Qt Creator.
                          I am running it on MacOS 14.2, Qt version 6.5.3

                          MesrineM Offline
                          MesrineM Offline
                          Mesrine
                          wrote on last edited by
                          #16

                          @KejPi
                          Do you run the application that is on the build directory or the installed one?

                          Try putting
                          set_source_files_properties(qml/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)

                          before

                          qt_add_executable(appSingletonTest
    main.cpp
)

                          in your minimal example.
                          If that does not work try removing some macos properties in the CMakeLists.txt.
                          If nothing works I would say you can open a bug as suggested by @ekkescorner

                          K 1 Reply Last reply
                          0
                          • MesrineM Mesrine

                            @KejPi
                            Do you run the application that is on the build directory or the installed one?

                            Try putting
                            set_source_files_properties(qml/Colors.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)

                            before

                            qt_add_executable(appSingletonTest
    main.cpp
)

                            in your minimal example.
                            If that does not work try removing some macos properties in the CMakeLists.txt.
                            If nothing works I would say you can open a bug as suggested by @ekkescorner

                            K Offline
                            K Offline
                            KejPi
                            wrote on last edited by KejPi
                            #17

                            @Mesrine I run the application directly from Qt Creator after building it.
                            Moving set_source_files_properties did not help, the problem is the same.

                            Bug report created https://bugreports.qt.io/browse/QTBUG-121758

                            1 Reply Last reply
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