QML receives undefined for roles from dataChanged signal

KiNgFrUiT

QML function and connection code is as follows:

    property var mode: 0
    property var status: 1

    function barrierDataChanged(topLeft, bottomRight, roles) {
        console.log("dataChanged", topLeft, bottomRight, roles, roles.length)

        var modelIndex = barrierModel.getBarrierIndex(barrierId)

        if(topLeft.row == modelIndex) {
            if(roles.contains("mode")) { // contains function is just a guess for now
                mode = barrierModel.get(modelIndex).mode
            }
            else if(roles.contains("status")) { // contains function is just a guess for now
                status = barrierModel.get(modelIndex).status
            }
        }
    }

    Connections {
        target: barrierModel
        onDataChanged: barrierDataChanged(topLeft, bottomRight, roles)
    }

p3c0

Alright. What are you going to do once you get those values in barrierDataChanged ?
I think you should probably rephrase your original question. I dont see any connection between your question I have a QAbstractItemListModel QAbstractListModel that works ok but updates are not very efficient, not all roles need to be updated. and the code you posted.

KiNgFrUiT

Currently I need to update mode and status every time dataChanged is emitted, as I cannot tell which role has changed.

If I can get the role parameter to contain useful data, instead of undefined, then the desired implementation will be more efficient as only the variable associated with the changed role needs updating.

Existing Code:

    property var mode: 0
    property var status: 1

    function barrierDataChanged(topLeft, bottomRight) {
        var modelIndex = barrierModel.getBarrierIndex(barrierId)

        if(topLeft.row == modelIndex) {
             mode = barrierModel.get(modelIndex).mode
             status = barrierModel.get(modelIndex).status
        }
    }

    Connections {
        target: barrierModel
        onDataChanged: barrierDataChanged(topLeft, bottomRight)
    }

Desired Code:

    property var mode: 0
    property var status: 1

    function barrierDataChanged(topLeft, bottomRight, roles) {
        console.log("dataChanged", topLeft, bottomRight, roles, roles.length)

        var modelIndex = barrierModel.getBarrierIndex(barrierId)

        if(topLeft.row == modelIndex) {
            if(roles.contains("mode")) { // contains function is just a guess for now
                mode = barrierModel.get(modelIndex).mode
            }
            else if(roles.contains("status")) { // contains function is just a guess for now
                status = barrierModel.get(modelIndex).status
            }
        }
    }

    Connections {
        target: barrierModel
        onDataChanged: barrierDataChanged(topLeft, bottomRight, roles)
    }

p3c0

@KiNgFrUiT Are you talking something as shown in the following example ?
http://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html#qabstractitemmodel-subclass

KiNgFrUiT

Yes, in that example the Animal roles are type and size.
In my application the roles are mode and status etc, I have simplified my code for this discussion.

    enum BarrierRole
    {
        BarrierIdRole = Qt::UserRole + 1,
        NameRole,
        ModeRole,
        StatusRole,
        BulbCountRole,
        BulbFaultsRole,
        InductionLoopRole
    };

p3c0

@KiNgFrUiT The only possibility left according to me(or try finding a way to make QVector available to QML, may be Q_DECLARE_METATYPE?? not sure) here is to create a Q_INVOKABLE in C++ model and call it from QML. This function will take arguments as both QModelIndex and the QVector<int> of roles. Then this function will resolve the values and return the data to QML.
For eg:
C++

QVariant MyModel::getValueByRole(QModelIndex t, QModelIndex b, QVector<int> role)
{
    qDebug() << t.data(role[0]);
}

QML

myModel.getValueByRole(topLeft, bottomRight, roles)

p3c0

@KiNgFrUiT It works in Qt 5.7. I just went through the documentation on the web and the installed one. I was using Qt 5.6 earlier. There were differences. It seems that they have made available QVector<int> to QML in the latest version. If you are still looking for this issue try upgrading Qt to the latest version.

p3c0

@p3c0 But as expected it returns an int and since as per your code you require a string to compare you will need some additional code on CPP side to get role value from the key. For eg:

QString MyModel::getRoleValue(int key)
{
    return roleNames().value(key);
}

This will return rolename string using the key that you receive in onDataChanged handler's roles parameter. eg. roles[0], roles[1] ...

Or instead you can directly get the value using data() which requires a QModelIndex and the role.

var str = myModel.data(topLeft, roles[0])

KiNgFrUiT

I just updated to 5.7, as per your suggestion, and everything works as expected.
Thank you so much for your assistance on this issue.

p3c0

@KiNgFrUiT You're Welcome :) Happy Coding.