Getting C++ struct in QML as type

akshaybabloo

I am on Qt 6.8. I am able to get the struct data in the QML but I am not able to get it as a type. The application name is DataLogStream and here is my struct:

#ifndef SERIALPORTSETTINGS_H
#define SERIALPORTSETTINGS_H

#include <QObject>
#include <QSerialPort>
#include <QMetaType>
#include <QQmlEngine>

struct SerialPortSettings {
    Q_GADGET
    QML_VALUE_TYPE(serialPortSettings)

    Q_PROPERTY(QString name MEMBER name)
    Q_PROPERTY(qint32 baudRate MEMBER baudRate)
    Q_PROPERTY(QString stringBaudRate MEMBER stringBaudRate)
    Q_PROPERTY(QSerialPort::DataBits dataBits MEMBER dataBits)
    Q_PROPERTY(QString stringDataBits MEMBER stringDataBits)
    Q_PROPERTY(QSerialPort::Parity parity MEMBER parity)
    Q_PROPERTY(QString stringParity MEMBER stringParity)
    Q_PROPERTY(QSerialPort::StopBits stopBits MEMBER stopBits)
    Q_PROPERTY(QString stringStopBits MEMBER stringStopBits)
    Q_PROPERTY(QSerialPort::FlowControl flowControl MEMBER flowControl)
    Q_PROPERTY(QString stringFlowControl MEMBER stringFlowControl)
    Q_PROPERTY(bool localEchoEnabled MEMBER localEchoEnabled)
    Q_PROPERTY(QString delimiter MEMBER delimiter)
    Q_PROPERTY(QString samplingFrequency MEMBER samplingFrequency)
    Q_PROPERTY(QString headerLength MEMBER headerLength)
    Q_PROPERTY(bool mergePlots MEMBER mergePlots)

public:
    QString name;
    qint32 baudRate;
    QString stringBaudRate;
    QSerialPort::DataBits dataBits;
    QString stringDataBits;
    QSerialPort::Parity parity;
    QString stringParity;
    QSerialPort::StopBits stopBits;
    QString stringStopBits;
    QSerialPort::FlowControl flowControl;
    QString stringFlowControl;
    bool localEchoEnabled;
    QString delimiter;
    QString samplingFrequency;
    QString headerLength;
    bool mergePlots;
};

Q_DECLARE_METATYPE(SerialPortSettings)

#endif // SERIALPORTSETTINGS_H

I then added this to SOURCE under qt_add_qml_module. I have portselectionservice.cpp/.h which is a QML_ELEMENT, which has all the setter and getter for this SerialPortSettings. The portselectionservice.cpp/.h can be called through PortSelection.qml by its type after importing DataLogStream in QML. And on a click of a button, the struct data is sent from PortSelection.qml to PlotStream.qml.

And I am trying to use this type as a property with:

import DataLogStream

ApplicationWindow {
    width: 1080
    height: 720

    property SerialPortSettings portSelectionSettings
    // ....
}

Now when I try to use SerialPortSettings or serialPortSettings as a property type, I am getting an error SerialPortSettings is not a type same for serialPortSettings. But if I just use it as var - property var portSelectionSettings - I am able to see the data.

Here is the DataLogStream.qmltypes

import QtQuick.tooling 1.2

// This file describes the plugin-supplied types contained in the library.
// It is used for QML tooling purposes only.
//
// This file was auto-generated by qmltyperegistrar.

Module {
    Component {
        file: "plotstreamservice.h"
        name: "PlotStreamService"
        accessSemantics: "reference"
        prototype: "QObject"
        exports: ["DataLogStream/PlotStreamService 0.0"]
        exportMetaObjectRevisions: [0]
        Property { ...}
    }
    Component {
        file: "portselectionservice.h"
        name: "PortSelectionService"
        accessSemantics: "reference"
        prototype: "QObject"
        exports: ["DataLogStream/PortSelectionService 0.0"]
        exportMetaObjectRevisions: [0]
        Property { ...}
        Method { name: "start" }
    }
    Component {
        file: "serialportsettings.h"
        name: "SerialPortSettings"
        accessSemantics: "value"
        exports: ["DataLogStream/serialPortSettings 0.0"]
        isCreatable: false
        exportMetaObjectRevisions: [0]
        Property { ... }
        
    }
}

The SerialPortSettings exists but the typesystem can't seem to catch it. How should I use the proper type here without causing an error?

Asperamanca

I think you missed one of the requirements, see https://doc.qt.io/qt-6/qtqml-cppintegration-definetypes.html#registering-value-types
"In contrast to object types, value types require lower case names."

Asperamanca

Somewhere in your build folder, you should be able to find a generated file containing the QML type registrations. They end with "_qmltyperegistrations.cpp", and should start with the name of the QML module.
Please check if your type is registered there.
If not, the problem is on the C++ or possibly cmake side
If it is, more likely on the user (QML) side

Asperamanca

Also, do you import the QML module by the correct name in QML?

akshaybabloo

@Asperamanca said in Getting C++ struct in QML as type:

Somewhere in your build folder, you should be able to find a generated file containing the QML type registrations. They end with "_qmltyperegistrations.cpp", and should start with the name of the QML module.
Please check if your type is registered there.
If not, the problem is on the C++ or possibly cmake side
If it is, more likely on the user (QML) side

Yes, it did create it and here is the output

/****************************************************************************
** Generated QML type registration code
**
** WARNING! All changes made in this file will be lost!
*****************************************************************************/

#include <QtQml/qqml.h>
#include <QtQml/qqmlmoduleregistration.h>

#if __has_include(<plotstreamservice.h>)
#  include <plotstreamservice.h>
#endif
#if __has_include(<portselectionservice.h>)
#  include <portselectionservice.h>
#endif
#if __has_include(<serialportsettings.h>)
#  include <serialportsettings.h>
#endif


#if !defined(QT_STATIC)
#define Q_QMLTYPE_EXPORT Q_DECL_EXPORT
#else
#define Q_QMLTYPE_EXPORT
#endif
Q_QMLTYPE_EXPORT void qml_register_types_DataLogStream()
{
    qmlRegisterModule("DataLogStream", 0, 0);
    QT_WARNING_PUSH QT_WARNING_DISABLE_DEPRECATED
    qmlRegisterTypesAndRevisions<PlotStreamService>("DataLogStream", 0);
    qmlRegisterTypesAndRevisions<PortSelectionService>("DataLogStream", 0);
    qmlRegisterTypesAndRevisions<SerialPortSettings>("DataLogStream", 0);
    QT_WARNING_POP
    qmlRegisterModule("DataLogStream", 0, 1);
}

static const QQmlModuleRegistration dataLogStreamRegistration("DataLogStream", qml_register_types_DataLogStream);

Also, do you import the QML module by the correct name in QML?

Yes, I did. i have been using import DataLogStream

Asperamanca

I think you missed one of the requirements, see https://doc.qt.io/qt-6/qtqml-cppintegration-definetypes.html#registering-value-types
"In contrast to object types, value types require lower case names."

akshaybabloo

I did - QML_VALUE_TYPE(serialPortSettings) - isn't this the way? Or do you mean it should be completely be in lower cases?

Asperamanca

You are right. I mis-read the requirements to apply to the C++ type name.

akshaybabloo

@Asperamanca I tried to change the whole text to lowercase and that worked!