[Solved] New TreeView does not connect to C++ model.

[Kofr]

Hello guys, I was waiting long time before Qt 5.5 has been released because of new TreeView component.
I am trying in agony to make it work with my model in C++ for a week.
So, I am completely stuck in understanding how all this "kitchen" works.

    //main.qml
    
    import QtQuick 2.4
    import QtQuick.Controls 1.4
    import QtQuick.Window 2.2
    import dataModel 1.0
    
    ApplicationWindow {
        title: qsTr("Hello World")
        width: 640
        height: 480
        visible: true
    
        menuBar: MenuBar {
            Menu {
                title: qsTr("&File")
                MenuItem {
                    text: qsTr("&Open")
                    onTriggered: messageDialog.show(qsTr("Open action triggered"));
                }
                MenuItem {
                    text: qsTr("E&xit")
                    onTriggered: Qt.quit();
                }
            }
        }
    
        TreeView {
            anchors.fill: parent
            model: DataModel
            TableViewColumn {
    
                title: "Name"
                role: "DisplayRole"
                width: 300
    
            }
        }
    }

    //main.cpp
    #include <QApplication>
    #include <QQmlApplicationEngine>
    #include <QtGui>
    #include <QtQml>
    
    #include "treemodel.h"
    
    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
    
        QQmlApplicationEngine engine;
        qmlRegisterType<TreeModel>("dataModel", 1, 0, "DataModel");
        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    
        return app.exec();
    }

    //task.h
    
    #ifndef TASK_H
    #define TASK_H
    #include <QList>
    #include <QVariant>
    
    
    class Task
    {
    public:
        explicit Task(const QString &data, Task *parent = 0);
        ~Task();
    
        void appendChild(Task *child);
    
        Task *child(int row) const {return m_childItems.value(row);}
        int childCount() const;
        int columnCount() const {return 1;}
        QVariant data(int column) const;
        int row() const;
    
        QString getName() const {return name;}
    
        Task *parentItem();
    
    
    
    private:
        QList<Task*> m_childItems;
        //QList<QVariant> m_itemData;
        Task *m_parentItem;
        QString name;//data element for a while
    };
    
    #endif // TASK_H

    //task.cpp
    
    
    #include "task.h"
    #include <QVariant>
    #include <QDebug>
    
    Task::Task(const QString &data, Task *parent)
    {
        m_parentItem = parent;
        name = data;//to be modified
    }
    
    //Task::Task(QObject *parent) : QObject(parent)
    //{
    //    m_parentItem = parent;
    //}
    
    Task::~Task()
    {
    
    }
    
    void Task::appendChild(Task *child)
    {
        m_childItems.append(child);
        qDebug() << "appending a child";//it does not event shows
    }
    
    int Task::childCount() const
    {
        return m_childItems.count();
    
    }
    
    int Task::row() const
    {
        if (m_parentItem)
            return m_parentItem->m_childItems.indexOf(const_cast<Task*>(this));
        return -1;
    }
    
    Task *Task::parentItem()
    {
        return m_parentItem;
    }

    //treemodel.h
    
    #ifndef TREEMODEL_H
    #define TREEMODEL_H
    #include <QAbstractItemModel>
    #include "task.h"
    
    
    class TreeModel : public QAbstractItemModel
    {
    public:
        //TreeModel();
        explicit TreeModel(QObject *parent = 0);
        QModelIndex index(int row, int column, const QModelIndex & parent = QModelIndex()) const Q_DECL_OVERRIDE;
        QModelIndex parent(const QModelIndex &index) const Q_DECL_OVERRIDE;
        ~TreeModel();
        int rowCount(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
        int columnCount(const QModelIndex &parent = QModelIndex()) const Q_DECL_OVERRIDE;
        QVariant data(const QModelIndex &index, int role) const Q_DECL_OVERRIDE;
    
        //void setupModelData(Task *parent);
    
    
        /*enum RoleNames {
            TaskNameRole = Qt::UserRole,
            TaskDateCreatedRole = Qt::UserRole + 1,
            TaskParentsRole = Qt::UserRole+2,
            TaskChildrensRole = Qt::UserRole+3,
            BrightnessRole = Qt::UserRole+4
        };*/
    private:
        QList<Task> m_data;
        Task * rootItem;
        //QHash<int, QByteArray> m_roleNames;
    };
    
    #endif // TREEMODEL_H

    //treemodel.cpp
    
    #include "treemodel.h"
    #include "task.h"
    
    TreeModel::TreeModel(QObject *parent)
        : QAbstractItemModel(parent)
    {
        rootItem = new Task(QString("default name"));
        //    m_roleNames[TaskNameRole] = "name";
        //    m_roleNames[TaskDateCreatedRole] = "dateCreated";
        //    m_roleNames[TaskParentsRole] = "parents";
        //    m_roleNames[TaskChildrensRole] = "childrens";
        //    m_roleNames[BrightnessRole] = "brightness";//to be changed
        //setupModelData(rootItem); //t
        rootItem->appendChild(new Task("alala1", rootItem) );
    }
    
    QModelIndex TreeModel::index(int row, int column, const QModelIndex &parent) const
    {
        if (!hasIndex(row, column, parent))
            return QModelIndex();
    
        Task *parentItem;
    
        if (!parent.isValid())
            parentItem = rootItem;
        else
            parentItem = static_cast<Task*>(parent.internalPointer());
    
        Task *childItem = parentItem->child(row);
        if (childItem)
            return createIndex(row, column, childItem);
        else
            return QModelIndex();
        //Q_UNUSED(parent);
        //if (row >= pkts.count() || row < 0 || column >= 8)
        //  return QModelIndex();
    
        //QStringList *pkt = pkts[row];
    
        //return createIndex(row, column, 0/*No Hierarchy yet*/);
    
    }
    
    QModelIndex TreeModel::parent(const QModelIndex &index) const
    {
        if (!index.isValid())
            return QModelIndex();
    
        Task *childItem = static_cast<Task*>(index.internalPointer());
        Task *parentItem = childItem->parentItem();
    
        if (parentItem == rootItem)
            return QModelIndex();
    
        return createIndex(parentItem->row(), 0, parentItem);//0 because tree structure. Trees have only children in first column
    }
    
    int TreeModel::rowCount(const QModelIndex &parent) const
    {
        Task *parentItem;
        /*if (parent.column() > 0)
            return 0;*/
    
        if (!parent.isValid())
            parentItem = rootItem;
        else
            parentItem = static_cast<Task*>(parent.internalPointer());
    
        return parentItem->childCount();
    }
    
    int TreeModel::columnCount(const QModelIndex &parent) const
    {
        if (parent.isValid())
            return static_cast<Task*>(parent.internalPointer())->columnCount();
        else
            return rootItem->columnCount();
    }
    QVariant TreeModel::data(const QModelIndex &index, int role) const
    {
        if (!index.isValid())
            return QVariant();
    
        if (role != Qt::DisplayRole)
            return QVariant();
    
        Task *item = static_cast<Task*>(index.internalPointer());
        return item->getName();//for a while
    
    
    }
    
    //void TreeModel::setupModelData(Task *parent)
    //{
    
    //}
    
    TreeModel::~TreeModel()
    {
        delete rootItem;
    }

How to make TreeView to show what is inside my C++ model? Please correct me if you see some bullsh!t!

[p3c0]

Hi @Kofr,
I find 2 issues here:

• When using C++ models subclassed from item models always re-implement roleNames because that it how the C++ model comes to know which data to send to the QML.

• You have registered the component using qmlRegisterType but not initialized it in QML. You will need to do this:

DataModel {
    id: myModel
}

and then assign it

TreeView {
    anchors.fill: parent
    model: myModel
}

OR
instead you can also set the model as a context property in main.cpp

TreeModel treemodel;
engine.rootContext()->setContextProperty("myModel",treemodel);
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

[Kofr]

@p3c0 thank you. How to know which role the Tree to show?

            title: "Name"
            role: "DisplayRole"
            width: 300
        }

does this mean that now our Tree shows Qt::DisplayRole ??

I am listing my TreeModel::data() function to show that it must return data with any role. However this function is never called (no debug messages).

QVariant TreeModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid()) {
        qDebug() << "data() - index is invalid";//it does not event shows
        return QVariant();
    }

    //if (role != Qt::DisplayRole)
      //  return QVariant();

    Task *item = static_cast<Task*>(index.internalPointer());
    qDebug() << "data() - Data is about to be returned";//it does not event shows
    return item->getName();//for a while
}

[p3c0]

@Kofr No. These roles are different and should match exactly with those in C++ model. This problem is all due to roles not found. Re-implement the roleNames as follows:

QHash<int, QByteArray> TreeModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[TypeRole] = "DisplayRole";
    return roles;
}

//and define role names
enum RoleNames {
    TypeRole = Qt::UserRole + 10,
};

//and then in data() ofcourse use as
if (role != TypeRole)
        return QVariant();

[Kofr]

@p3c0 Great success! Now it works.
stage 1 is complete. Now running to make it editable.

[p3c0]

@Kofr Nice. Happy Coding..

[Valerian]

@Kofr @p3c0
I need some help regarding re-ordering of the item of the QAbstractItemModel. I have put a MouseArea in the itemDelegate which allows me to drag an item. I need some help to call C++ function of the QAbstractItemModel to move items to support the dynamic re-ordering. Kindly advice

[Kofr]

@Valerian I did not do d&d yet. In my idea you should register a signal to be emitted whenever you move mouse in the area of new position and call swap function.
Do you feel something like this?

[Sumana]

@Kofr I am stuck into a similar problem, Can you by any chance provide the working code where the TreeView(with parent-child relation) is editable too? Considering that this post was really long back, but it will be a huge help if the code (completed with the qml and C++ too) is provided! Thanks in advance!