Singleton and QML in QT 6.3

RangerQT

I am at my wits end with this. I've searched, found "solutions" but nothing works.
I am running Qt 6.3.2 and Qt Creator 8

The application builds with no errors, starts but the window does not display. If I hardcode the color it runs.

In a course I took they simply setup the qml.dir file and then imported the styles directory into the myqml module but the course was for Qt 5.

Any help is appreciated .

Thank you.

I have added this to the CMakeLists.txt file with no luck.

# Set QML singleton
set_source_files_properties(Style.qml PROPERTIES QT_SINGLETON_TYPE TRUE)

I have set qmldir as below and then imported using the import statement shown below.
I have the following

singleton Style 1.0 Style.qml

main.qml
style (directory)
Style.qml
qmldir
ui (directory)
myqml.qml

Style.qml is as singleton:

pragma Singleton
import QtQuick

QtObject {
    id: root

    // Global Items
    property string theme: "AML"

    // Main menu items
    property int menuWidth: (rootWindow.width / 4)
    property int menuHeight: (rootWindow.height)
    property string menubgColor: "orange"
    property string menuItemColor: "pink"

}
 in my myqml.qml I have the following.  If I set the rectangle color to a string such as "orange" everything works fine but if I try and use Style.menubgColor for the color the app builds, starts (the exe is in the task manager list) but never displays anything.

import QtQuick
import "../styles"

Item {
id: root

property string currentItemName: mainMenuList.currentItemName

signal menuItemClicked(var name)


Rectangle {
    id: mainmenuColorFill
    width: parent.width
    height: rootWindow.height
    color: Style.menubgColor // "orange"
    MainMenuList {
        id:mainMenuList
        anchors.centerIn: parent
    }
} // End Rectangle mainMenuColorFill

} // End Item root

JKSH

@RangerQT said in Singleton and QML in QT 6.3:

I have set qmldir as below

Since you are using Qt 6.3, don't create qmldir files manually. Use qt_add_qml_module() instead. See https://www.qt.io/blog/introduction-to-the-qml-cmake-api

import "../styles"

This syntax is for importing a folder from disk. But you don't have a QML folder deployed with your application -- the Qt 6 CMake API is designed to build your QML code into a library (which is statically linked to your application, ideally)

Set a URI in qt_add_qml_module() and import that URI instead.

RangerQT

Hmm. I'm trying to get my head around this <G>. The last time I used Qt was Qt 5 with pro files. I will read that article - again for the nth time!

You mention static linking so I assume Qt 6 CMake does that for me and I don't have to tell it to do a static library.
Thank you.

1). Do I understand we do not need import statements anymore in QML since the qt_add_qml_module should pull them all in so I can access properties, etc without the import statement in my qml files. When would I have a QML folder deployed. I guess I thought that is what the ui and styles were - folders to import but from what you say the CMakeLists.txt should handle that.
So I do import FlightLog which is my URI (no quotes around FlightLog) and that should work. Yes, that works so I just do FlightLog which is my URI instead of the import "somedir".

2). Do I need a CMakeLists.txt in each subdirectory or is the one CMakeLists.txt at the project level okay. I assume not but I see examples with CMakeLIsts.txt in subdirectories but then they have cpp and h files in them.

3). I have this in CMakeLists.txt so should this be okay to include all my *.qml files? I am assuming it's okay to do something like ui/AppWindow.qml and styles/Style.qml in the QML_FILES list.

qt_add_executable(FlightLogbook
    main.cpp
)


# QML and other files
qt_add_qml_module(FlightLogbook
    URI FlightLog
    VERSION 1.0
    QML_FILES
        main.qml
        ui/AppWindow.qml
        ui/MainMenu.qml
        ui/MainMenuList.qml
        styles/Style.qml
    SOURCES
        import/import.h
        import/import.cpp
)

4). Do I need the set_source_files_properties(Style.qml PROPERTIES QT_SINGLETON_TYPE TRUE) in my CMakeLists.txt?

5.) I can do color: "orange" in the Rectangle but if I try color: Style.menubgColor the app builds, starts, but no window comes up. Style is recognized and when I hit the . it gives me the properties in the file so for some reason it must not like how I am using it to color the rectangle. This is with and without the pragma statement.

RangerQT

A followup to this. First I like the cmake process a lot and how things are handled in Qt6 vs Qt5 so far.

I still can not get a property defined in one qml file used in another. I get a unable to assign [undefined] to QColor. However, if I define the property in this file.

// Qt Imports
import QtQuick

// Our Imports
import FlightLog

Item {
    id: root

    property string currentItemName: mainMenuList.currentItemName

    signal menuItemClicked(var name)

    Rectangle {
        id: mainmenuColorFill
        width: parent.width
        height: rootWindow.height
        color: CustomStyles.menubgColor //  "orange"
        MainMenuList {
            id:mainMenuList
            anchors.centerIn: parent
        }

    } // End Rectangle mainMenuColorFill

} // End Item root

The CustomStyles.qml file is

// Qt Imports
import QtQuick

// Our Imports
//import FlightLog

QtObject {
    id: customStyles
    property string menubgColor: "purple"
}

However, if I define a property string testcolor: "purple" in main.qml I can use mainqlmwindowid.testcolor and it works.

I did try customStyles.menubgcolor in the MainMenu.qml file and it fails also.

Given it works with the definition in main.qml I assume it means the build did not include the CustomStyles.qml.

thomaso

Hi @RangerQT , did you find a solution to your question? I am fighting with something similar (but using qmake, not cmake yet)

RangerQT

@thomaso said in Singleton and QML in QT 6.3:

Hi @RangerQT , did you find a solution to your question? I am fighting with something similar (but using qmake, not cmake yet)

I never did and stopped pursuing that. Right now I'm working on getting other parts of my application working and then I'll revisit Singletons since I do need them.

blues-breaker

Is set_source_files_properties(styles/Style.qml PROPERTIES QT_SINGLETON_TYPE TRUE) before the qt_add_qml_module line in your CMakeLists.txt?

Also in your set_source_files_properties call you posted above you seem to be omitting the styles/ prefix from the file name which may also be the issue .

I suspect the generated qmldir is not marking your Style.qml file as a singleton which can be easily checked by inspecting the generated file. I also encountered this issue and for me it was caused by incorrect ordering in the CMakeLists.txt file like I mentioned above.

RangerQT

@blues-breaker
Thanks for that. I'll give it a try.

IAlexI

I've been looking for a solution for a long time, but finally figured it out: you have a typo in your source file property name, it is QT_QML_SINGLETON_TYPE, not QT_SINGLETON_TYPE . If you add

set_source_files_properties(Style.qml PROPERTIES QT_QML_SINGLETON_TYPE TRUE)

Before qt_add_qml_modules, the singleton works without any manual qmldir or c++ code

RangerQT

@IAlexI
Arrgh. So simple! And where to put it is another part of the puzzle. Thank you all.

DrSnowLabs

Hi all.

Just to help out anyone else who get into singleton issues, I also found out that having singletons in a sub-directory doesn't work using set_source_files_properties.

Please take a look at this thread.

kaushikv

@DrSnowLabs @IAlexI
I am also running into this issue.

I have several custom component in a separate directly which is like a common library for example myTextBox.qml , myTextFiled.qml

and i have a Style.qml file at the same location.

I have added Style.qml in CMAKE:

This sets up the singleton module Style to be used across the application

set_source_files_properties(Style.qml PROPERTIES
QT_QML_SINGLETON_TYPE TRUE
)

but still I can' access Style.properties inside the same directory or from another library which uses these common custom components.

any ideas to resolve this issue?

ekkescorner

@DrSnowLabs also take a look at https://www.qt.io/blog/implicit-imports-vs.-qml-modules-in-qt-6