How to Create a Generic Object Model for Use in QML?

How to Create a Generic Object Model for Use in QML

To register a Qt model as a property of a QObject, you can utilize the Q_PROPERTY macro. However, not all model types are compatible with this approach.

Using AnimalModel

While it's common to pass a QAbstractListModel directly to a QML view, it's not possible to register it as a property of a QObject using Q_PROPERTY.

Creating a Dynamic Object Model

To overcome this limitation, you can create a custom QObject that holds models of any data type. Consider the following example:

class DataObject : public QObject
{
    Q_OBJECT

    Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
    Q_PROPERTY(QString color READ color WRITE setColor NOTIFY colorChanged)
    ...

    AnimalModel m_modelAnimals;

    Q_PROPERTY(AnimalModel *modelAnimals READ modelAnimals NOTIFY modelAnimalsChanged)
};

This creates a QObject with a property that returns a pointer to the AnimalModel. The model can then be accessed in QML like this:

DataObject {
    modelAnimals: {
        // Manipulate the model here
    }
}

Schema-less Models

If you desire more flexibility, you can create schema-less models that allow objects with arbitrary properties. To achieve this:

1. Create a QAbstractListModel or QObject model that stores QObject .
2. Provide a single object role that returns the object.
3. Use a Loader as a delegate to instantiate different QML UI implementations based on the object type.
4. Implement QQmlListProperty and Q_CLASSINFO("DefaultProperty", "container") for the model to allow dynamic composition using QML's declarative syntax.

Using List

Here's an example of a generic List model that supports various object types:

class List : public QAbstractListModel
{
    Q_OBJECT
    QList<QObject *> _data;

    ...
};

You can register this model using:

qmlRegisterType<List>("Core", 1, 0, "List");

And use it in QML as follows:

List {
    QtObject { ... }
    QtObject { ... }
    List {
        QtObject { ... }
        QtObject { ... }
    }
}

Dynamic Sorting and Filtering

To make this model more usable, you can implement a sorting and filtering proxy:

class SortingFilteringProxy : public QAbstractListModel
{
    Q_OBJECT
    QSortFilterProxyModel _proxy;

    ...
};

This allows for advanced filtering and sorting capabilities based on arbitrary properties of the contained objects.

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