Singleton QML failed to load as module

nsourl

Hi,

I am using Qt 5.15.0 and created a singleton QML file and tried to load it as a module using qmldir.

But unfortunately, I am receiving an error when QQmlApplicationEngine is trying to load the component.

What I am doing wrong and getting this frustrating output? Any ideas what's happening?

Below you can find all the information needed to help me out.

Thanks!

Application output

QQmlApplicationEngine failed to load component
<Unknown File>:12:5: Composite Singleton Type TestMe is not creatable.

TestMe.qml

pragma Singleton
import QtQuick 2.0

Item {
    readonly property string value: "value"
}

main.qml

import QtQuick 2.15
import QtQuick.Window 2.15

import base 1.0

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

    TestMe {
        value: "new value"
    }
}

qmldir

module base
singleton TestMe 1.0 TestMe.qml

qmake

QML_IMPORT_PATH = $$PWD/imports

main.cpp

    QQmlApplicationEngine engine;
    engine.addImportPath("qrc:/imports");
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

Project structure screenshot

KroMignon

@nsourl said in Singleton QML failed to load as module:

But the same result as before and the error message exactly the same. I performed a complete clean on the project and QML/JS before running application.

Sorry, I read too quickly your first post.
As you have defined TestMe as singleton, you can not create any instance of it, because its already exists!

Change your main.qml as follow, it should than work:

import QtQuick 2.15
import QtQuick.Window 2.15

import base 1.0

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

    Component.onCompleted: TestMe.value ="new value"
}

KroMignon

@nsourl said in Singleton QML failed to load as module:

What I am doing wrong and getting this frustrating output? Any ideas what's happening?

AFAIK only QtObject modules can be singletons not Item.
Change TestMe.qml from Item to QtObject and it should works as expected.
cf . https://wiki.qt.io/Qml_Styling

nsourl

@KroMignon

AFAIK only QtObject modules can be singletons not Item.
Change TestMe.qml from Item to QtObject and it should works as expected.
cf . https://wiki.qt.io/Qml_Styling

Thank you for your prompt reply. In the beginning, I had it with QtObject and changed it back now.

But the same result as before and the error message exactly the same. I performed a complete clean on the project and QML/JS before running application.

KroMignon

@nsourl said in Singleton QML failed to load as module:

But the same result as before and the error message exactly the same. I performed a complete clean on the project and QML/JS before running application.

Sorry, I read too quickly your first post.
As you have defined TestMe as singleton, you can not create any instance of it, because its already exists!

Change your main.qml as follow, it should than work:

import QtQuick 2.15
import QtQuick.Window 2.15

import base 1.0

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

    Component.onCompleted: TestMe.value ="new value"
}

nsourl

@KroMignon

Sorry, I read your too quickly your first post.
As you have defined TestMe as singleton, you can not create any instance of it, because its already exists!

Change your main.qml as follow, it should than work:
import QtQuick 2.15
import QtQuick.Window 2.15

import base 1.0

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

    Component.onCompleted: TestMe.value ="new value"
}

Oh yeah you are absolutely right, since it's a singleton the instance already exists!

Of course now it works as expected! :)

Thank you for your help!