How to create dependency between 2 columns using combobox delegates in MVC

[Santosh Reddy]

Here you go, run this code.

I used delegate (because I used standard model) but you could do the similar in the your custom model.

#include <QtWidgets>
 
class Delegate : public QStyledItemDelegate
{
public:
    explicit Delegate(QObject * parent = 0) : QStyledItemDelegate(parent) {}
 
    QWidget * createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const
    {
        QComboBox * widget = new QComboBox(parent);
 
        widget->addItems(index.data(Qt::UserRole+1).toStringList());
 
        return widget;
    }
 
    void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const
    {
        if(index.column() == 0)
        {
            QComboBox * widget = dynamic_cast<QComboBox *>(editor);
 
            if(widget)
            {
                QString country = widget->currentText();
 
                QVariant russia = QStringList() << "Moscow" << "Saint Petersburg" << "Novosibirsk" << "Yekaterinburg";
                QVariant canada = QStringList() << "Toronto"  << "Parliament Hill" << "Quebec" << "Montreal";
                QVariant china  = QStringList() << "Shanghai" << "Beijing" << "Chongqing" << "Hong Kong";
                QVariant states = QStringList() << "New York City" << "Los Angeles" << "Chicago" << "Houston";
 
                QModelIndex nextColumnIndex = model->index(index.row(), 1);
 
                if(country == "Russia")
                {
                    model->setData(nextColumnIndex, russia, Qt::UserRole+1);
                }
                else if(country == "Canada")
                {
                    model->setData(nextColumnIndex, canada, Qt::UserRole+1);
                }
                else if(country == "China")
                {
                    model->setData(nextColumnIndex, china, Qt::UserRole+1);
                }
                else if(country == "United States")
                {
                    model->setData(nextColumnIndex, states, Qt::UserRole+1);
                }
 
                model->setData(index, country);
                model->setData(nextColumnIndex, "Select City Again");
            }
            widget->addItems(index.data(Qt::UserRole+1).toStringList());
        }
        else
        {
            QStyledItemDelegate::setModelData(editor, model, index);
        }
    }
};
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QTableView table;
    QStandardItemModel model(4, 2);
 
    for (int row = 0; row < 4; row++)
    {
        QStandardItem *item = new QStandardItem(QString("Select Country").arg(row).arg(0));
        item->setData(QStringList() << "Russia" << "Canada" << "China" << "United States",Qt::UserRole+1);
        model.setItem(row, 0, item);
 
        item = new QStandardItem(QString("Select City").arg(row).arg(1));
        item->setData(QStringList());
        model.setItem(row, 1, item);
    }
 
    table.setModel(&model);
    table.setItemDelegate(new Delegate(&model));
    table.show();
 
    return app.exec();
}

#include <QtWidgets>

class Delegate : public QStyledItemDelegate
{
public:
    explicit Delegate(QObject * parent = 0) : QStyledItemDelegate(parent) {}

    QWidget * createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const
    {
        QComboBox * widget = new QComboBox(parent);

        widget->addItems(index.data(Qt::UserRole+1).toStringList());

        return widget;
    }

    void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const
    {
        if(index.column() == 0)
        {
            QComboBox * widget = dynamic_cast<QComboBox *>(editor);

            if(widget)
            {
                QString country = widget->currentText();

                QVariant russia = QStringList() << "Moscow" << "Saint Petersburg" << "Novosibirsk" << "Yekaterinburg";
                QVariant canada = QStringList() << "Toronto"  << "Parliament Hill" << "Quebec" << "Montreal";
                QVariant china  = QStringList() << "Shanghai" << "Beijing" << "Chongqing" << "Hong Kong";
                QVariant states = QStringList() << "New York City" << "Los Angeles" << "Chicago" << "Houston";

                QModelIndex nextColumnIndex = model->index(index.row(), 1);

                if(country == "Russia")
                {
                    model->setData(nextColumnIndex, russia, Qt::UserRole+1);
                }
                else if(country == "Canada")
                {
                    model->setData(nextColumnIndex, canada, Qt::UserRole+1);
                }
                else if(country == "China")
                {
                    model->setData(nextColumnIndex, china, Qt::UserRole+1);
                }
                else if(country == "United States")
                {
                    model->setData(nextColumnIndex, states, Qt::UserRole+1);
                }

                model->setData(index, country);
                model->setData(nextColumnIndex, "Select City Again");
            }
            widget->addItems(index.data(Qt::UserRole+1).toStringList());
        }
        else
        {
            QStyledItemDelegate::setModelData(editor, model, index);
        }
    }
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QTableView table;
    QStandardItemModel model(4, 2);

    for (int row = 0; row < 4; row++)
    {
        QStandardItem *item = new QStandardItem(QString("Select Country").arg(row).arg(0));
        item->setData(QStringList() << "Russia" << "Canada" << "China" << "United States",Qt::UserRole+1);
        model.setItem(row, 0, item);

        item = new QStandardItem(QString("Select City").arg(row).arg(1));
        item->setData(QStringList());
        model.setItem(row, 1, item);
    }

    table.setModel(&model);
    table.setItemDelegate(new Delegate(&model));
    table.show();

    return app.exec();
}

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