Qt:如何使用自定义模型在QListView中实现简单的内部拖放来对项目进行重新排序

#include <QtWidgets>

class CustomModel : public QAbstractListModel
{
public:
    CustomModel(QObject *parent = nullptr)
        : QAbstractListModel(parent)
    {
        m_data << "Item 1" << "Item 2" << "Item 3" << "Item 4" << "Item 5";
    }

    int rowCount(const QModelIndex &parent = QModelIndex()) const override
    {
        return m_data.count();
    }

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override
    {
        if (!index.isValid() || index.row() >= m_data.count())
            return QVariant();

        if (role == Qt::DisplayRole)
            return m_data[index.row()];

        return QVariant();
    }

    Qt::ItemFlags flags(const QModelIndex &index) const override
    {
        if (!index.isValid())
            return Qt::NoItemFlags;

        return Qt::ItemIsEnabled | Qt::ItemIsSelectable | Qt::ItemIsDragEnabled | Qt::ItemIsDropEnabled;
    }

    bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override
    {
        if (index.isValid() && role == Qt::EditRole)
        {
            m_data[index.row()] = value.toString();
            emit dataChanged(index, index);
            return true;
        }

        return false;
    }

    Qt::DropActions supportedDropActions() const override
    {
        return Qt::MoveAction;
    }

    bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) override
    {
        beginInsertRows(parent, row, row + count - 1);
        for (int i = 0; i < count; ++i)
            m_data.insert(row, "");
        endInsertRows();
        return true;
    }

    bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override
    {
        beginRemoveRows(parent, row, row + count - 1);
        for (int i = 0; i < count; ++i)
            m_data.removeAt(row);
        endRemoveRows();
        return true;
    }

    Qt::DropActions supportedDragActions() const override
    {
        return Qt::MoveAction;
    }

    QStringList mimeTypes() const override
    {
        return QStringList() << "text/plain";
    }

    QMimeData *mimeData(const QModelIndexList &indexes) const override
    {
        QMimeData *mimeData = new QMimeData();
        QByteArray encodedData;

        QDataStream stream(&encodedData, QIODevice::WriteOnly);
        for (const QModelIndex &index : indexes)
        {
            if (index.isValid())
            {
                QString text = data(index, Qt::DisplayRole).toString();
                stream << text;
            }
        }

        mimeData->setData("text/plain", encodedData);
        return mimeData;
    }

    bool dropMimeData(const QMimeData *data, Qt::DropAction action, int row, int column, const QModelIndex &parent) override
    {
        if (action == Qt::IgnoreAction)
            return true;

        if (!data->hasFormat("text/plain"))
            return false;

        if (column > 0)
            return false;

        int beginRow;

        if (row != -1)
            beginRow = row;
        else if (parent.isValid())
            beginRow = parent.row();
        else
            beginRow = rowCount(QModelIndex());

        QByteArray encodedData = data->data("text/plain");
        QDataStream stream(&encodedData, QIODevice::ReadOnly);

        QStringList newItems;
        int rows = 0;

        while (!stream.atEnd())
        {
            QString text;
            stream >> text;
            newItems << text;
            ++rows;
        }

        if (rows == 0)
            return false;

        insertRows(beginRow, rows, QModelIndex());

        for (const QString &text : newItems)
        {
            QModelIndex index = createIndex(beginRow++, 0);
            setData(index, text);
        }

        return true;
    }

private:
    QStringList m_data;
};

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

    QListView listView;
    CustomModel model;
    listView.setModel(&model);
    listView.setDragEnabled(true);
    listView.setAcceptDrops(true);
    listView.setDropIndicatorShown(true);
    listView.setDefaultDropAction(Qt::MoveAction);
    listView.setSelectionMode(QAbstractItemView::SingleSelection);
    listView.setDragDropMode(QAbstractItemView::InternalMove);

    listView.show();

    return app.exec();
}