Trouble importing supporting QML files into Main.QML

I'm trying to make a QtQuick app with color themes. I plan to make a few .qml style sheets that define concepts like buttonColor, fontColor and so on. Here's an example of what the style sheets will look like more or less:

pragma Singleton
import QtQuick

QtObject {
    property color bodyTextColor: "white"
    property color headerTextColor: "black"
    property int buttonBorderWidth: 3
    property color buttonColor: "#007bff"
    property color backgroundColor: "#000000"
    property color accentColor: "#6c757d"
    property int fontSize: 16
    property int titleFontSize: fontSize + 8
    property int labelFontSize: fontSize - 16
}

I tried import "ClassicStylesheet.qml" as Styles and it can't find it even though it's in the same root directory with Main.qml (I get a "no such directory" error). Using an absolute path to ClassicStylesheet.qml gets around this and the app runs, but it still doesn't work. I get the following error:

Could not find any constructor for value type QQuickColorValueType to call with value QVariant(QObject*, 0x0) qrc:/[projectname]/Main.qml:31:17: Unable to assign undefined to QColor

All components render in black when running with an absolute path to the style sheet. Here's an example of my Main.qml file using my reusable LargeButton component (which renders fine using defaults, without the stylesheet) to create a main menu button:

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts

import "ClassicStylesheet.qml" as Styles

Window {
    width: 1280
    height: 720
    visible: true
    title: qsTr("Test")

    Rectangle {
        id: menuFrame
        width: 600
        height: 400
        color: "lightgrey"
        anchors.centerIn: parent
        radius: 25

        ColumnLayout {
            anchors.centerIn: parent
            spacing: 10

            LargeButton {
                text: "Settings"
                buttonColor: Styles.buttonColor
                accentColor: Styles.accentColor
                fontColor: Styles.fontColor

                onClicked:
                {

                }
            }
        }
    }
}

Any advice on navigating this? Why doesn't it recognize my file or read its contents? Thanks.

Solution

There's no need to import a singleton file. You might need to supply a qmldir file.

singleton AppThemes 1.0 AppThemes.qml

In the following demo, there are two themes. A "light" and "dark" theme. These are available via the AppThemes singleton. The standard Palette format is used so that it can be assigned at a top-level component and it will be inherited by all controls underneath. Additional parameters, such as fontSize may be added.

import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
Page {
    title: "AppThemes Demo"
    palette: AppThemes.current.palette
    ColumnLayout {
        RowLayout {
            AppButton { text: "File" }
            AppButton { text: "Edit" }
            AppButton { text: "Settings" }
            AppButton { text: "Help" }
        }
        AppLabel { text: "Pick a Theme" }
        Repeater {
            model: AppThemes.themes
            AppButton {
                text: modelData
                checked: modelData === AppThemes.currentName
                onClicked: AppThemes.currentName = modelData
            }
        }
    }
}

// qmldir
singleton AppThemes 1.0 AppThemes.qml

// AppThemes.qml
pragma Singleton
import QtQuick
AppThemesPrivate {
}

// AppThemesPrivate.qml
import QtQuick
QtObject {
    id: appThemes
    readonly property list<string> themes: ["light","dark"]
    property string currentName: "light"
    readonly property AppStyle current: appThemes[currentName] || light
    property AppStyle light: AppStyle {
    }
    property AppStyle dark: AppStyle {
        fontSize: 14
        palette: Palette {
            alternateBase: "#000"
            base: "#000"
            button: "#111"
            buttonText: "#fff"
            dark: "#666"
            highlight: "#d73"
            highlightedText: "#000"
            light: "#000"
            mid: "#444"
            midlight: "#333"
            placeholderText: "#80000000"
            shadow: "#888"
            text: "#fff"
            window: "#222"
            windowText: "#fff"
        }
    }
}

// AppStyle.qml
import QtQuick
import QtQuick.Controls
QtObject {
    property int fontSize: 10
    property Palette palette: Palette {
        alternateBase: "#fff"
        base: "#fff"
        button: "#eee"
        buttonText: "#000"
        dark: "#999"
        highlight: "#38c"
        highlightedText: "#fff"
        light: "#fff"
        mid: "#bbb"
        midlight: "#ccc"
        placeholderText: "#80000000"
        shadow: "#777"
        text: "#000"
        window: "#fff"
        windowText: "#000"
    }
}

// AppButton.qml
import QtQuick
import QtQuick.Controls
Button {
    font.pointSize: AppThemes.current.fontSize
}

// AppLabel.qml
import QtQuick
import QtQuick.Controls
Label {
    font.pointSize: AppThemes.current.fontSize
}

You can Try it Online!

References:

https://doc.qt.io/qt-6/qtqml-modules-qmldir.html