Returning and Enum to QML using a Q_INVOKABLE method

[kzawada]

Is it possible to pass enums from a C++ Q_OBJECT class using Q_INVOKABLE to a QML implementation. There is an error that I am getting with it:

@main.qml:185: Error: Unknown method return type: FaultWarningItem::ItemType@

This happens when I attempt to return a enum as part of the Q_INVOKABLE:
@Q_INVOKABLE FaultWarningItem::ItemType getItemErrorType(void);@

[SGaist]

Hi and welcome to devnet,

Did you register your enum ?

See this "thread":http://qt-project.org/forums/viewthread/16497 for an example

[chezgi]

there is some limits on using enums from qml.
you can't use another classes enums for Q_INVOKABLE functions.
your enums only can be used for primary classes functions.

[kzawada]

Indeed this is the case there is a problem with this. I was hoping to use this to explicitly do apple-to-apple comparison: (1) make the *.qml file easily readable by replacing hard coded numbers, (2) force errors when interpreting *.qml files when enum changes, and (3) make the code easily searchable to enum item.

However, there is a limitation here that I will not be able to get around.

My code is the following:

FaultWarningItem.h
@#ifndef FAULTWARNINGITEM_H
#define FAULTWARNINGITEM_H
#include <QObject>

// Fault Warning Container Class
class FaultWarningItem
{
Q_GADGET
Q_ENUMS(ItemType)
public:

enum ItemType
{
    TypeUnspecified = -1,
    TypeNoError = 0,
    TypeWarning,
    TypeFault
};

};

#endif // FAULTWARNINGITEM_H@

FaultWarningModel.h
@#ifndef FAULTWANRINGMODEL_H
#define FAULTWANRINGMODEL_H

#include <QObject>
#include "FaultWarningItem.h"

class FaultWarningModel: public QObject {
Q_OBJECT
public:
FaultWarningModel(QObject *parent=0);

~FaultWarningModel();

Q_INVOKABLE FaultWarningItem::ItemType getItemErrorType(void) const;
Q_INVOKABLE int getItemErrorTypeAsInt(void) const;

Q_INVOKABLE void setNextFaultWarning();

int getCount() const;

private:
int m_count;
FaultWarningItem::ItemType m_FaultWarningItem;
signals:
void countChanged(int);
};

#endif // FAULTWANRINGMODEL_H@

FaultWarningModel.cpp
@#include "FaultWarningModel.h"
#include <QQml.h>
#include <QDebug>

FaultWarningModel::FaultWarningModel(QObject *parent) :
QObject(parent)
{

m_FaultWarningItem = FaultWarningItem::TypeUnspecified;

int statusType = qmlRegisterUncreatableType<FaultWarningItem>
                 (
                     "ItemType",                                          // const char * uri,
                     1,                                                   // int versionMajor,
                     0,                                                   // int versionMinor,
                     "ItemType",                                          // const char * qmlName,
                     "ItemType type cannot be created." // const QString & message
                 );

qDebug() << "statusType: " << statusType;

}

FaultWarningItem::ItemType FaultWarningModel::getItemErrorType(void) const
{
return m_FaultWarningItem;
}

int FaultWarningModel::getItemErrorTypeAsInt() const
{
int iValue = (int) m_FaultWarningItem;
return iValue;
}
@

main.qml

@import QtQuick 2.0

// The enum types need to be imported before they can be used.
import ItemType 1.0

Rectangle {
width: 200
height: 300

property int currentFaultWarningType: ItemType.TypeUnspecified

Column {
    anchors.horizontalCenter: parent.horizontalCenter
    anchors.verticalCenter: parent.verticalCenter
    spacing: 10

    // Toggles the printer type
    Rectangle {
        id: buttonFaultWaring

        width: 100
        height: 50

        color: "gainsboro"

        border.color: "black"
        border.width: 1

        Text {
            text: "TOGGLE Fault/Warning Type"
            width: parent.width
            anchors.centerIn: parent
            wrapMode: Text.WordWrap
            horizontalAlignment: Text.AlignHCenter
        }

        MouseArea {
            anchors.fill: parent
            onClicked: {
                FaultWarningModel.setNextFaultWarning();
                currentFaultWarningType = FaultWarningModel.getItemErrorTypeAsInt();
            }
        }
    }

    // Shows the type of the printer
    Rectangle {
        id: statusFaultWarning

        width: 100
        height: 50

        Text {
           text: {
               // Causes - "Error: Unknown method return type: FaultWarningItem::ItemType"
               //currentFaultWarningType = FaultWarningModel.getItemErrorType()

               // Causes - "Error: Unknown method return type: FaultWarningItem::ItemType"
               /*if (ItemType.TypeUnspecified === FaultWarningModel.getItemErrorType())
               {
                   "Yay, it works"
               }*/

               currentFaultWarningType = FaultWarningModel.getItemErrorTypeAsInt()
               if (ItemType.TypeUnspecified === currentFaultWarningType)
               {
                   "TypeUnspecified (-1)"
               }
               else if (ItemType.TypeNoError === currentFaultWarningType)
               {
                   "TypeNoError (0)"
               }
               else if (ItemType.TypeWarning === currentFaultWarningType)
               {
                   "TypeWarning (1)"
               }
               else if (ItemType.TypeFault === currentFaultWarningType)
               {
                   "TypeFault (2)"
               }
               else
               {
                   "?"
               }
           }

           anchors.centerIn: parent
       }
    }
}

}@

Is there any future plans in Qt to have this changed so that it can be used without getting "Error: Unknown method return type"?

[chezgi]

see https://codereview.qt-project.org/#change,73812
it seems that something changed at 5.3.0
try it.

[kafanti]

It is already old topic but I would like to reply for documentation purposes for further questions,
If you like to use an enum on a Q_INVOKABLE function, then this enum should be registered.

https://bugreports.qt.io/browse/QTBUG-19741