QML ListModel for interaction with C++

[shock]

Because i am using setPos() to place these items in the DeclarativeView

[wysota]

They are part of your data and not items. The model makes no use of their declarative item nature. If you delete such an object behind the model's back, your application will crash the next time the model tries to use that item.

The proper approach would be to have some internal representation of your data that is shared between the model and the item you display somewhere in the scene.

[shock]

I don't know if i got your point, but that is (as i think) exactly what i do?
I changed the interface design later to:

class QMLPtrAbstractItem : public QDeclarativeItem
{
public:
    virtual ~QMLPtrAbstractItem() { }
 
    virtual bool setData(int role, const QVariant &value) = 0;
    virtual QVariant getData(int role) const = 0;
 
    virtual int getUID() const = 0;
    virtual void setUID(int uid) = 0;
};

class QMLPtrAbstractItem : public QDeclarativeItem
{
public:
    virtual ~QMLPtrAbstractItem() { }

    virtual bool setData(int role, const QVariant &value) = 0;
    virtual QVariant getData(int role) const = 0;

    virtual int getUID() const = 0;
    virtual void setUID(int uid) = 0;
};

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So that i have an abstract "interface" to the model then i derive other classes of QMLPtrAbstractItem

class EmpData : public QMLPtrAbstractItem

class EmpData : public QMLPtrAbstractItem

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I could have also done:

class QMLPtrAbstractItem {}
class EmpData : public QMLPtrAbstractItem, public QDeclarativeItem {}

class QMLPtrAbstractItem {}
class EmpData : public QMLPtrAbstractItem, public QDeclarativeItem {}

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But the Abstractlayer is my communication layer between the DeclarativeItem and the Model - or have i missed something?
I am using only Data in the model - the data i get from the Item itself (i wanted to avoid to implement 3 different model for the same type of use case...

In the Model i call "getData()" in data() to return the data associated with the provided role (different acting for different item)
The model holds a list of pointers to the Items (as usual!?) and with data() I request the data for a given role from the selected item

Isn't that the same behaviour as usual? The same is done here: http://harmattan-dev.nokia.com/docs/...model-cpp.html

This is what i do: (looks the same for me)

QVariant QMLPtrNotificationModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() > lst.size())
        return QVariant();
 
    const QMLPtrAbstractItem * const ptrItem = lst[index.row()];
 
    return ptrItem->getData(role);
}
 
bool QMLPtrNotificationModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (index.row() >= 0 && index.row() < lst.size()) {
 
        QMLPtrAbstractItem * const ptrItem = lst.at(index.row());
        if(ptrItem){
            bool changed = ptrItem->setData(role, value);
 
            if(changed)
                emit dataChanged(index, index);
            return changed;
        }
        return false;
    }else
        qDebug() << "QMLPtrNotificationModel::setData( " << role << ")";
 
    return false;
}

QVariant QMLPtrNotificationModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() > lst.size())
        return QVariant();

    const QMLPtrAbstractItem * const ptrItem = lst[index.row()];

    return ptrItem->getData(role);
}

bool QMLPtrNotificationModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (index.row() >= 0 && index.row() < lst.size()) {

        QMLPtrAbstractItem * const ptrItem = lst.at(index.row());
        if(ptrItem){
            bool changed = ptrItem->setData(role, value);

            if(changed)
                emit dataChanged(index, index);
            return changed;
        }
        return false;
    }else
        qDebug() << "QMLPtrNotificationModel::setData( " << role << ")";

    return false;
}

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What's wrong with that architecture? If you say -you must be right because you have more knowhow than me, but if that's "bad design" i could have missed the point - i am always interested in your opinion

[wysota]

You are still using QDeclarativeItem as the base class for items in your model.

Isn't that the same behaviour as usual? The same is done here: http://harmattan-dev.nokia.com/docs/...model-cpp.html

No, it's not. In the quoted example Animal is not a subclass of QDeclarativeItem.

[shock]

Ok.. so you mean this would be better?:

class QMLPtrAbstractItem
{
}
 
class QMLPtrNotificationModel : public QAbstractListModel
{
....
private:
    QList<QMLPtrAbstractItem*> lst;
};
 
class EmpData : public QDeclarativeItem, public QMLPtrAbstractItem
{
....
}

class QMLPtrAbstractItem
{
}

class QMLPtrNotificationModel : public QAbstractListModel
{
....
private:
    QList<QMLPtrAbstractItem*> lst;
};

class EmpData : public QDeclarativeItem, public QMLPtrAbstractItem
{
....
}

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[wysota]

What is this EmpData class? Are you adding instances of this class directly to the declarative scene? Your initial QML code suggests the only custom item you are using is "TaskData". How is "EmpData" related to "TaskData"?

[shock]

EmpData and TaskData are items that i really add to the DeclarativeView - EmpData is not really related to TaskData (That are employees - TaskData are the Tasks that are associated to the Employees which are represented via to the DeclatativeView via EmpData)
They are however threated similar to Tasks TaskData is created the same way:

class TaskData : public QDeclarativeItem, public QMLPtrAbstractItem

class TaskData : public QDeclarativeItem, public QMLPtrAbstractItem

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From TaskData there are however again two specifications: Events (sickness, Vacation) and Orders (real working tasks) Task is the "interface for both"

So OrderData and EventData are then derived from TaskData...

EventData *td = new EventData();
    td->setUID(ID.toInt());
    td->setName(type);
    td->setBgColor1("#ffffff");
    td->setBgColor2(color.name());
    td->setXPos(x);
    td->setYPos(y);
    td->setLength(w);
    td->setCreationUser(creationUser);
    taskModel.addElement(td);

EventData *td = new EventData();
    td->setUID(ID.toInt());
    td->setName(type);
    td->setBgColor1("#ffffff");
    td->setBgColor2(color.name());
    td->setXPos(x);
    td->setYPos(y);
    td->setLength(w);
    td->setCreationUser(creationUser);
    taskModel.addElement(td);

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OrderData *td = new OrderData();
    td->setUID(uID);
    td->setName(text);
    td->setBgColor1("#ffffff");
    td->setBgColor2(ZEGlobal->getStatusColor(oid2sta[orderID]).name());
    td->setXPos(ex_x);
    td->setYPos(ex_y);
    td->setLength(len);
    td->setOrderID(orderID);
    td->setLttID(lttID);
    td->setGrpID(grpID);
    td->setCreationUser(creationUser);
    taskModel.addElement(td);

OrderData *td = new OrderData();
    td->setUID(uID);
    td->setName(text);
    td->setBgColor1("#ffffff");
    td->setBgColor2(ZEGlobal->getStatusColor(oid2sta[orderID]).name());
    td->setXPos(ex_x);
    td->setYPos(ex_y);
    td->setLength(len);
    td->setOrderID(orderID);
    td->setLttID(lttID);
    td->setGrpID(grpID);
    td->setCreationUser(creationUser);
    taskModel.addElement(td);

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These items are later checked for collisions - but i think i got your point ... i don't need the DeclarativeItem ... cauze the items are placed via
the data from the model in QML..
Was that your point?

[wysota]

Ok, I think the problem is that you are not using QtQuick correctly. It's a declarative framework, not an imperative one. Your TaskData and EmpData classes are delegates -- components that should be used to display (and otherwise interact with) data from a model. They are not supposed to be part of the model itself so you don't need to add them manually to the scene. You just need to state "ok, here is a model containing my data and here is how each item should look like".

So based on that your EmpData class can have the same base class as your model item class but that's not required in any way, you just need to teach the EmpData class to handle pieces of data from your model. Instead of inheritance you can as well use composition.

class EmpDataItem : public QDeclarativeItem {
  Q_OBJECT
  Q_PROPERTY(QString name READ name WRITE setName)
public:
  void setName(const QString &n) {
    m_data.name = n;
    update();
  }
  QString name() const { return m_data.name; }
private:
  EmpData m_data;
};

class EmpDataItem : public QDeclarativeItem {
  Q_OBJECT
  Q_PROPERTY(QString name READ name WRITE setName)
public:
  void setName(const QString &n) {
    m_data.name = n;
    update();
  }
  QString name() const { return m_data.name; }
private:
  EmpData m_data;
};

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This way you won't require any virtual methods in your data class and you can easily have the model class hold QList<Data> instead of QList<Data*> which makes things a lot easier.

[shock]

Hmm what you say sounds good so far..
"Your TaskData and EmpData classes are delegates -- components that should be used to display (and otherwise interact with) data from a model" I agree to that and got that (i think)..
Means I have Delegates that don't have any data by heart and the delegates are provided X-times according to the Listmodel which holds the data for each Delegate - this might be set via setItemData() correct? And in the delegate I can access the data via the role.

What for do i need the QDeclarativeItem anyways? If the Delegate interacts with the model that thing is not needed? By now it is working without it..

If i store the data in the model directly i have to use different model instances - correct? At the moment i am using one instance for Tasks and Events thats why i
used virtual functions and the Abstractlayer

What would you do with

private:
EmpData m_data;
};

private:
EmpData m_data;
};

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in the case above ? how does the model interact with that Data?

[wysota]

and the delegates are provided X-times according to the Listmodel which holds the data for each Delegate

The delegate is provided once per view using the "delegate" property of the view. The model itself doesn't use a delegate.

this might be set via setItemData() correct? And in the delegate I can access the data via the role.

No, that's wrong, that's my point that you are doing it the wrong way. Your model shouldn't be composed of delegates or anything like that. The model holds data, regardless of how the data is stored. You don't need any "items" in the model, the data could be generated on the fly. The "items" are not "delegates", they have no visual representation in the model.

What for do i need the QDeclarativeItem anyways?

The way I see it you are providing a custom delegate (TaskData or EmpData). If you implement it in C++, it will be derived from QDeclarativeItem.

By now it is working without it..

You have QDeclarativeItem instances all over your code, just take a look.

If i store the data in the model directly i have to use different model instances

Different model instances of what?

how does the model interact with that Data?

The model doesn't interact with data. The model represents the data, it provides access to it.

[shock]

You have QDeclarativeItem instances all over your code, just take a look.

This is the structure that works for me by now:

class QMLPtrAbstractItem : public QObject
{
	Q_OBJECT
public:
    virtual ~QMLPtrAbstractItem() { }
 
    virtual bool setData(int role, const QVariant &value) = 0;
    virtual QVariant getData(int role) const = 0;
 
    virtual int getUID() const = 0;
    virtual void setUID(int uid) = 0;
};
 
class EmpData : public QMLPtrAbstractItem
{
    Q_OBJECT
public:
    enum EmpRoles {
        Name = Qt::UserRole + 1,
        UID,
		Qualification
    };
 
    static QHash<int, QByteArray> getQMLRoles(){
        QHash<int, QByteArray> roles;
        roles[Name]				= "name";
        roles[UID]				= "uid";
        roles[Qualification]    = "qualification";
        return roles;
    }
 
    EmpData()  {}
 
    virtual QVariant getData(int role) const {
        if (role == Name)
            return getName();
        else if (role == UID)
            return getUID();
        else if (role == Qualification)
            return getQualification();
        return QVariant();
    }
 
    virtual bool setData(int role, const QVariant &value) {
        bool changed = false;
        if (role == Name){
            changed = true;
            setName(value.toString());
        }
        else if (role == UID){
            changed = true;
            setUID(value.toInt());
        }
        else if (role == Qualification){
            changed = true;
            setQualification(value.toString());
        }
        return changed;
    }
 
private:
.....
};
 
class TaskData : public QMLPtrAbstractItem
{
    Q_OBJECT
 
public:
    enum TaskRoles {
        UID = Qt::UserRole + 1,
        Name,
        BgColor1,
        BgColor2,
        XPos,
        YPos,
        Length,
        CreationUser,
        OrderType,
        Active,
        Index
    };
 
    static QHash<int, QByteArray> getQMLRoles(){
        QHash<int, QByteArray> roles;
        roles[UID]          = "uid";
        roles[Name]         = "name";
        roles[BgColor1]     = "bgColor1";
        roles[BgColor2]     = "bgColor2";
        roles[XPos]         = "xPos";
        roles[YPos]         = "yPos";
        roles[Length]       = "length";
        roles[CreationUser] = "creationuser";
        roles[OrderType]    = "orderType";
        roles[Active]       = "active";
        roles[Index]        = "index";
        return roles;
    }
 
    TaskData()  {
        _bgcolor1 = "#FEFEFE";
        _bgcolor2 = "#ededeb";
        _active = false;
    }
    virtual ~TaskData() { }
 
.....
 
    QVariant getData(int role) const {
        if (role == UID)
            return getUID();
        else if (role == Name)
            return getName();
        else if (role == BgColor1)
            return getBgColor1();
        else if (role == BgColor2)
            return getBgColor2();
        else if (role == XPos)
            return getXPos();
        else if (role == YPos)
            return getYPos();
        else if (role == Length)
            return getLength();
        else if (role == CreationUser)
            return getCreationUser();
        else if (role == OrderType)
            return getOrderType();
        else if (role == Active)
            return isActive();
        else if (role == Index)
            return getIndex();
        return QVariant();
    }
 
    bool setData(int role, const QVariant &value) {
        bool changed = false;
        if (role == UID){
            changed = true;
            setUID(value.toInt());
        }
        else if (role == Name){
            changed = true;
            setName(value.toString());
        }
        else if (role == BgColor1){
            changed = true;
            setBgColor1(value.toString());
        }
        else if (role == BgColor2){
            changed = true;
            setBgColor2(value.toString());
        }
        else if (role == XPos){
            changed = true;
            setXPos(value.toInt());
        }
        else if (role == YPos){
            changed = true;
            setYPos(value.toInt());
        }
        else if (role == Length){
            changed = true;
            setLength(value.toInt());
        }
        else if (role == CreationUser){
            changed = true;
            setCreationUser(value.toInt());
        }
        else if (role == OrderType){
            changed = true;
            setOrderType(value.toInt());
        }
        else if (role == Active){
            changed = true;
            setActive(value.toInt());
        }
        else if (role == Index){
            changed = true;
            setIndex(value.toInt());
        }
        return changed;
    }
 
private:
 ....
};
 
class OrderData : public TaskData
{
    Q_OBJECT
 ....
}
 
class EventData : public TaskData
{
    Q_OBJECT
...
}
 
class QMLPtrNotificationModel : public QAbstractListModel
{
    Q_OBJECT
....
}
 
QVariant QMLPtrNotificationModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() > lst.size())
        return QVariant();
 
    const QMLPtrAbstractItem * const ptrItem = lst[index.row()];
 
    return ptrItem->getData(role);
}
 
bool QMLPtrNotificationModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (index.row() >= 0 && index.row() < lst.size()) {
 
        QMLPtrAbstractItem * const ptrItem = lst.at(index.row());
        if(ptrItem){
            bool changed = ptrItem->setData(role, value);
 
            if(changed)
                emit dataChanged(index, index);
            return changed;
        }
        return false;
    }else
        qDebug() << "QMLPtrNotificationModel::setData( " << role << ")";
 
    return false;
}

class QMLPtrAbstractItem : public QObject
{
	Q_OBJECT
public:
    virtual ~QMLPtrAbstractItem() { }

    virtual bool setData(int role, const QVariant &value) = 0;
    virtual QVariant getData(int role) const = 0;

    virtual int getUID() const = 0;
    virtual void setUID(int uid) = 0;
};

class EmpData : public QMLPtrAbstractItem
{
    Q_OBJECT
public:
    enum EmpRoles {
        Name = Qt::UserRole + 1,
        UID,
		Qualification
    };

    static QHash<int, QByteArray> getQMLRoles(){
        QHash<int, QByteArray> roles;
        roles[Name]				= "name";
        roles[UID]				= "uid";
        roles[Qualification]    = "qualification";
        return roles;
    }

    EmpData()  {}

    virtual QVariant getData(int role) const {
        if (role == Name)
            return getName();
        else if (role == UID)
            return getUID();
        else if (role == Qualification)
            return getQualification();
        return QVariant();
    }

    virtual bool setData(int role, const QVariant &value) {
        bool changed = false;
        if (role == Name){
            changed = true;
            setName(value.toString());
        }
        else if (role == UID){
            changed = true;
            setUID(value.toInt());
        }
        else if (role == Qualification){
            changed = true;
            setQualification(value.toString());
        }
        return changed;
    }

private:
.....
};

class TaskData : public QMLPtrAbstractItem
{
    Q_OBJECT

public:
    enum TaskRoles {
        UID = Qt::UserRole + 1,
        Name,
        BgColor1,
        BgColor2,
        XPos,
        YPos,
        Length,
        CreationUser,
        OrderType,
        Active,
        Index
    };

    static QHash<int, QByteArray> getQMLRoles(){
        QHash<int, QByteArray> roles;
        roles[UID]          = "uid";
        roles[Name]         = "name";
        roles[BgColor1]     = "bgColor1";
        roles[BgColor2]     = "bgColor2";
        roles[XPos]         = "xPos";
        roles[YPos]         = "yPos";
        roles[Length]       = "length";
        roles[CreationUser] = "creationuser";
        roles[OrderType]    = "orderType";
        roles[Active]       = "active";
        roles[Index]        = "index";
        return roles;
    }

    TaskData()  {
        _bgcolor1 = "#FEFEFE";
        _bgcolor2 = "#ededeb";
        _active = false;
    }
    virtual ~TaskData() { }

.....

    QVariant getData(int role) const {
        if (role == UID)
            return getUID();
        else if (role == Name)
            return getName();
        else if (role == BgColor1)
            return getBgColor1();
        else if (role == BgColor2)
            return getBgColor2();
        else if (role == XPos)
            return getXPos();
        else if (role == YPos)
            return getYPos();
        else if (role == Length)
            return getLength();
        else if (role == CreationUser)
            return getCreationUser();
        else if (role == OrderType)
            return getOrderType();
        else if (role == Active)
            return isActive();
        else if (role == Index)
            return getIndex();
        return QVariant();
    }

    bool setData(int role, const QVariant &value) {
        bool changed = false;
        if (role == UID){
            changed = true;
            setUID(value.toInt());
        }
        else if (role == Name){
            changed = true;
            setName(value.toString());
        }
        else if (role == BgColor1){
            changed = true;
            setBgColor1(value.toString());
        }
        else if (role == BgColor2){
            changed = true;
            setBgColor2(value.toString());
        }
        else if (role == XPos){
            changed = true;
            setXPos(value.toInt());
        }
        else if (role == YPos){
            changed = true;
            setYPos(value.toInt());
        }
        else if (role == Length){
            changed = true;
            setLength(value.toInt());
        }
        else if (role == CreationUser){
            changed = true;
            setCreationUser(value.toInt());
        }
        else if (role == OrderType){
            changed = true;
            setOrderType(value.toInt());
        }
        else if (role == Active){
            changed = true;
            setActive(value.toInt());
        }
        else if (role == Index){
            changed = true;
            setIndex(value.toInt());
        }
        return changed;
    }

private:
 ....
};

class OrderData : public TaskData
{
    Q_OBJECT
 ....
}

class EventData : public TaskData
{
    Q_OBJECT
...
}

class QMLPtrNotificationModel : public QAbstractListModel
{
    Q_OBJECT
....
}

QVariant QMLPtrNotificationModel::data(const QModelIndex &index, int role) const
{
    if (index.row() < 0 || index.row() > lst.size())
        return QVariant();

    const QMLPtrAbstractItem * const ptrItem = lst[index.row()];

    return ptrItem->getData(role);
}

bool QMLPtrNotificationModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    if (index.row() >= 0 && index.row() < lst.size()) {

        QMLPtrAbstractItem * const ptrItem = lst.at(index.row());
        if(ptrItem){
            bool changed = ptrItem->setData(role, value);

            if(changed)
                emit dataChanged(index, index);
            return changed;
        }
        return false;
    }else
        qDebug() << "QMLPtrNotificationModel::setData( " << role << ")";

    return false;
}

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QML looks like that:

Repeater {
        id: tasks
        model: taskModel // is registered via context() - holds OrderData and EventData via virtual binding
        delegate: TaskData { }
    }

Repeater {
        id: tasks
        model: taskModel // is registered via context() - holds OrderData and EventData via virtual binding
        delegate: TaskData { }
    }

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There is no QDeclarativeItem anymore - and it compiles and works

Different model instances of what?

Different Model instances: one for OrderData, one for EventData and one for EmpData

As i think the code will also work if i rename the classes to *Cpp? They just have the same names as the delegates - The QML delegate gets the
Data from the Model provided in the Repeater via accessing the roles of the model?!

TaskData.qml:

Text {
        id: taskName
        anchors.centerIn: parent
        text: name; // sets the name as text -> accesses the given model and executes data() for the role "name" which returns the name !?
         color: "white";
    }

Text {
        id: taskName
        anchors.centerIn: parent
        text: name; // sets the name as text -> accesses the given model and executes data() for the role "name" which returns the name !?
         color: "white";
    }

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Where is my structural error? =(

-------------------

I tried it by renamin the classes to *Cpp - works either

class EmpDataCpp : public QMLPtrAbstractItem { ... }
class TaskDataCpp : public QMLPtrAbstractItem { ... }
class OrderDataCpp : public TaskDataCpp { .. .}
class EventDataCpp : public TaskDataCpp { .. .}

class EmpDataCpp : public QMLPtrAbstractItem { ... }
class TaskDataCpp : public QMLPtrAbstractItem { ... }
class OrderDataCpp : public TaskDataCpp { .. .}
class EventDataCpp : public TaskDataCpp { .. .}

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With Delegates:

Repeater {
                id: empGrid
                model: empModel
                delegate: Employee { }
            }
    Repeater {
        id: tasks
        model: taskModel
        delegate: TaskData { }
    }

Repeater {
                id: empGrid
                model: empModel
                delegate: Employee { }
            }
    Repeater {
        id: tasks
        model: taskModel
        delegate: TaskData { }
    }

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[wysota]

You are making it much more complicated than it needs to be. The item class needs not inherit QObject since you are not using any QObject related functionality in it. Next thing is that your model doesn't do anything fancy, it has functionality similar to QStandardItemModel, so you can use that instead of a custom model you need to care about. Third of all if you really insist on using a custom model class, there is no point in having various subclasses of QMLPtrAbstractItem because neither of these subclasses add anything to their base class functionality. Fourth of all if you get rid of QObject legacy, you can use objects instead of pointers to objects in your model which reduces possibilities of making an error somewhere in code.

Currently your code is equivalent to:

class MyModel : public QStandardItemModel {
public:
  MyModel(QObject *parent = 0) : QStandardItemModel(parent) { setColumnCount(1); }
  void setRoles(const QHash<int, QByteArray> & roleNames) { setRoleNames(roleNames); }
};
 
enum EmpRoles { Name = Qt::DisplayRole, UID = Qt::UserRole, Qualification };
enum TaskRoles { Name = Qt::DisplayRole, UID = Qt::UserRole, ... }
QHash<int, QByteArray> empNames;
empNames[EmpRoles::Name] = "name";
empNames[EmpRoles::UID] = "uid";
// etc.
MyModel empModel;
empModel.setRoles(empNames);
 
 
 
QHash<int, QByteArray> taskNames;
taskNames[TaskRoles::Name] = "name";
taskNames[TaskRoles::UID] = "uid";
MyModel taskModel;
taskModel.setRoles(taskNames);

class MyModel : public QStandardItemModel {
public:
  MyModel(QObject *parent = 0) : QStandardItemModel(parent) { setColumnCount(1); }
  void setRoles(const QHash<int, QByteArray> & roleNames) { setRoleNames(roleNames); }
};

enum EmpRoles { Name = Qt::DisplayRole, UID = Qt::UserRole, Qualification };
enum TaskRoles { Name = Qt::DisplayRole, UID = Qt::UserRole, ... }
QHash<int, QByteArray> empNames;
empNames[EmpRoles::Name] = "name";
empNames[EmpRoles::UID] = "uid";
// etc.
MyModel empModel;
empModel.setRoles(empNames);



QHash<int, QByteArray> taskNames;
taskNames[TaskRoles::Name] = "name";
taskNames[TaskRoles::UID] = "uid";
MyModel taskModel;
taskModel.setRoles(taskNames);

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My code seems much shorter and less error prone than yours.