How to use pragma Singleton?

[jialuo]

I created a ThemeManager.qml to manage my theme.qml. But I can't use pragma Singleton in theme.qml. I won't be able to find the relevant properties.

ThemeManager.qml

import QtQuick 2.0

QtObject {
    property QtObject lightTheme: LightTheme
    property QtObject darkTheme: DarkTheme 
    property QtObject currentTheme: lightTheme

    function setTheme(theme) {
        if (theme === "light") {
            currentTheme = lightTheme
        } else if (theme === "dark") {
            currentTheme = darkTheme
        }
    }
}

LightTheme.qml

pragma Singleton

import QtQuick 2.0

QtObject {
    readonly property color textColor: "#000000"
    readonly property color backgroundColor: "#ffffff"
}

DarkTheme.qml

pragma Singleton
import QtQuick 2.0

QtObject {
    readonly property color textColor: "#ffffff"
    readonly property color backgroundColor: "#000000"
}

Main.qml

import QtQuick
import QtQuick.Window
import QtQuick.Controls

Window {
    visible: true
    width: 640
    height: 480

    property alias themeManager: themeManager

    ThemeManager {
        id: themeManager
    }

    Text {
        text: "Hello, world!"
        color: themeManager.currentTheme.textColor
        anchors.centerIn: parent
    }

    MouseArea {
        anchors.fill: parent
        onClicked: {
            themeManager.setTheme(
                        themeManager.currentTheme === themeManager.lightTheme ? "dark" : "light")
        }
    }
}

[christofer]

I wasn't able to get it to work with singleton, but I did get a theme swap to work that could be a globally accessible property of a root page (though I'm just doing it in one main.qml).

Here's the sample project with all the source.

--- ThemeManager.qml -----------

import QtQuick

QtObject {
    id: mgr

    property Loader loader: Loader {
        source: "BlueTheme.qml"
    }

    property QtObject theme: loader.item

    function swap() {
        if (loader.source == "BlueTheme.qml") {
            loader.source = "GreenTheme.qml"
        } else {
            loader.source = "BlueTheme.qml"
        }
    }
}

--- main.qml -----------

import QtQuick
import QtQuick.Layouts
import QtQuick.Controls

Window {
    id: window
    width: 500
    height: 300
    visible: true
    title: qsTr("Qt 6.5 QML Theme Swap")

    ThemeManager{
        id: tm
    }

    Rectangle {
        anchors.fill: parent
        color: tm.theme.aColor

        Button {
            id: theButton
            text: "swap"
            anchors.centerIn: parent
            onClicked: tm.swap()
        }
    }
}

[jeremy_k]

QML singletons used to require a qmldir entry. The Qt 6.5 documentation suggests that this is still the case.

[christofer]

@jeremy_k I'm using pragma singleton with Qt 6.5 without a qmldir file. For example, this has MyConstants.qml in the Base module.

[jeremy_k]

@christofer said in How to use pragma Singleton?:

@jeremy_k I'm using pragma singleton with Qt 6.5 without a qmldir file. For example, this has MyConstants.qml in the Base module.

That's great. Perhaps you can explain what was required, for the edification of the OP and future readers.

[christofer]

@jeremy_k
Here you go. Note that I didn't use a qmldir file.

// MyConstants.qml
pragma Singleton

import QtQuick

QtObject {
    readonly property int aNumber: 13
    readonly property color aColor: "teal"
    readonly property string someWords: "Words from MyConstants."
}

//main.qml
Window {
    color: MyConstants.aColor
}

But to see how it is wired together you need to see a whole project imho.

[christofer]

In case it helps. I minimized the example app to just the pragma Singleton stuff.

https://gitlab.com/christoferjennings/qt-6-5-modules-sandbox/-/tree/just-pragma-singleton