**Course Title:** Qt 6 Application Development with C++ **Section Title:** Model-View-Controller (MVC) Architecture in Qt **Topic:** Using QAbstractListModel and QAbstractTableModel for data models. ### Overview of QAbstractListModel and QAbstractTableModel In Qt 6, `QAbstractListModel` and `QAbstractTableModel` are two fundamental classes that provide the base implementation for data models. These classes enable you to manage and structure data in a way that can be easily accessed and manipulated by views. Understanding how to use these classes effectively is crucial for building robust and scalable applications. ### QAbstractListModel `QAbstractListModel` is an abstract base class that provides a basic implementation for list models. It is used to represent a list of items, where each item is a single data element. To use `QAbstractListModel`, you need to subclass it and override the following methods: * `data()`: Returns the data for a specific item. * `rowCount()`: Returns the number of items in the model. Here's a simple example of using `QAbstractListModel`: ```cpp // personmodel.h #ifndef PERSONMODEL_H #define PERSONMODEL_H #include <QAbstractListModel> #include <QStringList> class PersonModel : public QAbstractListModel { Q_OBJECT public: explicit PersonModel(QObject *parent = nullptr); // Header: [[nodiscard]] int rowCount(const QModelIndex &parent) const override; // Retrieve role names [[nodiscard]] QHash<int, QByteArray> roleNames() const override; // Retrieve data [[nodiscard]] QVariant data(const QModelIndex &index, int role) const override; void add(const QString &name); private: QStringList people; }; #endif // PERSONMODEL_H // personmodel.cpp #include "personmodel.h" PersonModel::PersonModel(QObject *parent) : QAbstractListModel(parent) { } int PersonModel::rowCount(const QModelIndex &parent) const { if (parent.isValid()) return 0; return people.size(); } QHash<int, QByteArray> PersonModel::roleNames() const { QHash<int, QByteArray> roles; roles[Qt::DisplayRole] = "name"; return roles; } QVariant PersonModel::data(const QModelIndex &index, int role) const { if (!index.isValid()) return QVariant(); if (role == Qt::DisplayRole) return people[index.row()]; else return QVariant(); } void PersonModel::add(const QString &name) { beginInsertRows(QModelIndex(), people.size(), people.size()); people << name; endInsertRows(); } ``` ### QAbstractTableModel `QAbstractTableModel` is an abstract base class that provides a basic implementation for table models. It is used to represent a table of items, where each item is a single data element. To use `QAbstractTableModel`, you need to subclass it and override the following methods: * `data()`: Returns the data for a specific item. * `rowCount()`: Returns the number of rows in the model. * `columnCount()`: Returns the number of columns in the model. Here's a simple example of using `QAbstractTableModel`: ```cpp // studentmodel.h #ifndef STUDENTMODEL_H #define STUDENTMODEL_H #include <QAbstractTableModel> #include <QString> #include <QVector> #include <memory> class StudentModel : public QAbstractTableModel { Q_OBJECT public: explicit StudentModel(QObject *parent = nullptr); // Header: [[nodiscard]] int rowCount(const QModelIndex &parent) const override; [[nodiscard]] int columnCount(const QModelIndex &parent) const override; // Retrieve role names [[nodiscard]] QHash<int, QByteArray> roleNames() const override; // Retrieve data [[nodiscard]] QVariant data(const QModelIndex &index, int role) const override; void addStudent(const QString &name, int age); private: QVector<std::pair<QString, int>> students; }; #endif // STUDENTMODEL_H // studentmodel.cpp #include "studentmodel.h" StudentModel::StudentModel(QObject *parent) : QAbstractTableModel(parent) { } int StudentModel::rowCount(const QModelIndex &parent) const { if (parent.isValid()) return 0; return students.size(); } int StudentModel::columnCount(const QModelIndex &parent) const { if (parent.isValid()) return 0; return 2; } QHash<int, QByteArray> StudentModel::roleNames() const { QHash<int, QByteArray> roles; roles[Qt::DisplayRole] = "name"; roles[Qt::UserRole + 1] = "age"; // Add 'age' as a separate column return roles; } QVariant StudentModel::data(const QModelIndex &index, int role) const { if (!index.isValid()) return QVariant(); const auto &student = students[index.row()]; if (role == Qt::DisplayRole) return student.first; else if (role == Qt::UserRole + 1) return student.second; return QVariant(); } void StudentModel::addStudent(const QString &name, int age) { beginInsertRows(QModelIndex(), students.size(), students.size()); students << std::make_pair(name, age); endInsertRows(); } ``` ### Advantages of Using QAbstractListModel and QAbstractTableModel * Separation of concerns: These classes help separate the data model from the view, making it easier to maintain and scale the application. * Reusability: By using these classes, you can reuse your data model across different views and platforms. * Efficient data handling: `QAbstractListModel` and `QAbstractTableModel` provide efficient data handling mechanisms, including support for lazy loading and caching. ### Conclusion `QAbstractListModel` and `QAbstractTableModel` are powerful classes in Qt 6 that help you manage and structure data in your applications. By understanding how to use these classes effectively, you can build robust, scalable, and maintainable applications. In the next topic, we will explore data binding between models and views. If you have any questions or need further clarification on the material covered, please let us know. Qt Documentation: * [QAbstractListModel Class](https://doc.qt.io/qt-6/qabstractlistmodel.html) * [QAbstractTableModel Class](https://doc.qt.io/qt-6/qabstracttablemodel.html)