Reference Error appears, but the program runs normally.

w.tkm · 16 Dec 2021, 08:40

Hi.
I get Reference Error, but runs without problems
It's very strange. What could be causing this?

Error String
ReferenceError: testcpp is not defined

main.qml

import QtQuick 2.15
import QtQuick.Window 2.15
import TestCpp 1.0

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

    TestCpp{
        id: testcpp
    }

    TestQml{
        id: testqml
    }
}

Test.qml

import QtQuick 2.0

Item {
    Rectangle{
        id: testRect
        width: 50
        height: 50
        color: "Red"
    }

    Component.onCompleted: {
        testcpp.fnTest(10)
    }
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "TestCpp.h"

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif

    qmlRegisterType<TestCpp>("TestCpp", 1, 0, "TestCpp");

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    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);

    return app.exec();
}

TestCpp.h

#ifndef TESTCPP_H
#define TESTCPP_H

#include <QObject>

class TestCpp : public QObject
{
    Q_OBJECT
public:
    TestCpp();
public slots:
    void fnTest(int Num);
};
#endif // TESTCPP_H

TestCpp.cpp

#include "TestCpp.h"
#include <QDebug>

TestCpp::TestCpp()
{

}

void TestCpp::fnTest(int Num)
{
    qDebug() << "Get Num: " << Num;
}

sierdzio · 16 Dec 2021, 07:22

@w-tkm said in Reference Error appears, but the program runs normally.:

testcpp.fnTest(10)

You try to access testcpp ID in a different file than where it is defined. This won't work, the IDs in QML are only in scope in the file where they are defined.

J.Hilk · 16 Dec 2021, 07:29

@sierdzio said in Reference Error appears, but the program runs normally.:

This won't work, the IDs in QML are only in scope in the file where they are defined.

thats actually not true, if it is than please correct me.
I had it, where, if an Id is not found in the local file, it was searched upwards in the parent tree until it found a fitting ID. This was the cause of a very confusing and lengthly debug session on my part.
I usually give my root element the id root, except that one time, where I didn't ....

sierdzio · 16 Dec 2021, 07:38

@J-Hilk read OP's code again. The line testcpp.fnTest(10) is written in completely different file than where TestCpp is instantiated. I'm 100% certain that ID is out of scope (and QML engine tells us that, too!).

If that line was in the same file - then sure, no problem, ID is visible in the whole file. Otherwise - nope. There is only one exception to this - delegate components can access IDs from other files, but it's pure magic. Better not use it.

J.Hilk · replied to sierdzio on 16 Dec 2021, 07:38

@sierdzio said in Reference Error appears, but the program runs normally.:

read OP's code again. The line testcpp.fnTest(10) is written in completely different file than where TestCpp is instantiated. I'm 100% certain that ID is out of scope (and QML engine tells us that, too!).

that I don't question, I don't even see an instantiation of Test.qml in the provided code

There is only one exception to this - delegate components can access IDs from other files, but it's pure magic. Better not use it.

I meant something like this:

//main.qml
import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    id:mainWindowRoot
    visible: true
    width: 640
    height: 480

    signal someRandomSignal()

    onSomeRandomSignal: console.log("Signal in mainWindowRoot")

    Test1{

    }
    Test2{

    }

}

//test1.qml
import QtQuick 2.12

Item {
    id: test1
    Timer{
        running: true
        interval: 1000
        repeat: true
        onTriggered: {
            console.log("test1 timer")
            mainWindowRoot.someRandomSignal()
        }
    }
}

//test2.qml
import QtQuick 2.12

Item {
    id: test2
    Timer{
        running: true
        interval: 1000
        repeat: true
        onTriggered: {
            console.log("test2 timer")
            mainWindowRoot.someRandomSignal()
        }
    }
}

output:

qml: test2 timer
qml: Signal in mainWindowRoot
qml: test1 timer
qml: Signal in mainWindowRoot
qml: test2 timer
qml: Signal in mainWindowRoot
qml: test1 timer
qml: Signal in mainWindowRoot
qml: test2 timer
qml: Signal in mainWindowRoot
qml: test1 timer
qml: Signal in mainWindowRoot
qml: test2 timer
qml: Signal in mainWindowRoot
qml: test1 timer
qml: Signal in mainWindowRoot
qml: test2 timer
qml: Signal in mainWindowRoot
qml: test1 timer
qml: Signal in mainWindowRoot

magic.

sierdzio · 16 Dec 2021, 07:43

Ah yes, I forgot about that one. ID of the main window is also global.

... it's a mess :-(

J.Hilk · replied to sierdzio on 16 Dec 2021, 07:43

@sierdzio said in Reference Error appears, but the program runs normally.:

Ah yes, I forgot about that one. ID of the main window is also global.
... it's a mess :-(

!
that I wasn't even aware off,
let me adjust my example:

//main.qml
import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    id:mainWindowRoot
    visible: true
    width: 640
    height: 480

    NotMainWindow{

    }

}  // Window

//notmainwindow.qml
import QtQuick 2.12

Item {
    id: notMainRoot

    signal someRandomSignal()

    onSomeRandomSignal: console.log("Signal not in mainWindowRoot, but in notMainRoot")

    Test1{

    }
    Test2{

    }
}

//test1.qml
import QtQuick 2.12

Item {
    id: test1
    Timer{
        running: true
        interval: 1000
        repeat: true
        onTriggered: {
            console.log("test1 timer")
            notMainRoot.someRandomSignal()
        }
    }
}

//test2.qml
import QtQuick 2.12

Item {
    id: test2
    Timer{
        running: true
        interval: 1000
        repeat: true
        onTriggered: {
            console.log("test2 timer")
            notMainRoot.someRandomSignal()
        }
    }
}

output:

qml: test2 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test1 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test2 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test1 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test2 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test1 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test2 timer
qml: Signal not in mainWindowRoot, but in notMainRoot
qml: test1 timer
qml: Signal not in mainWindowRoot, but in notMainRoot

sierdzio · wrote on 16 Dec 2021, 07:45

Whaaaat. I had no idea :D

KroMignon · 20 Dec 2021, 01:55

@w-tkm said in Reference Error appears, but the program runs normally.:

Hi.
I get Reference Error, but runs without problems
It's very strange. What could be causing this?
Error String
ReferenceError: testcpp is not defined

Perhaps it have nothing to do, but in main.qml, you use a component called TestQml but, according to your post, the QML file is called Test.qml and not TestQml.qml. It is just a typo?

KH-219Design · wrote on 16 Dec 2021, 18:05

My comment is in regards to "but runs without problems." I would amend that to say "it runs without problems.... for now." Over the long run, I suggest remaining ever-vigilant. But you are vigilant! That's the reason for this post! So good job :)

Whenever I see a post about QML warning messages, I feel compelled to repeat my QML "public service announcement" on the topic:

My belief: qml "warnings" are best treated as errors. Since QML is running inside a QML/Javascript interpreter hosted in your executable, QML doesn't have the right (the luxury?) to abort the application. So QML's best attempt to get your attention is by printing warnings, which are exceedingly easy to miss. The problem is made worse because QML warnings can appear when there is no user-facing bug happening, so we get lulled into ignoring the warnings as a matter of course. But usually when something finally causes a user-facing bug, there should be a QML warning that is relevant.

I have gone to great lengths to squash all QML warnings in my projects. (see: https://forum.qt.io/post/585598)

w.tkm · replied to KroMignon on 20 Dec 2021, 01:55

@KroMignon
Sorry, It's just a typo...