How Can I Pass Qt Models as QObject Properties in QML?

Passing Qt Model as QObject Property

Introduction

Creating a generic object model to use in QML can enhance code flexibility and data handling capabilities. This article explores various methods for passing Qt models as QObject properties, enabling QML objects to dynamically access and manipulate data from these models.

Using QAbstractListModel*

The simplest approach is to declare the property as QAbstractListModel*, as:

Q_PROPERTY(QAbstractListModel* modelAnimals READ modelAnimals NOTIFY modelAnimalsChanged)

This allows QML to access the model object and its underlying data. However, the property requires a pointer to the model, not the model itself.

Utilizing QQmlListProperty

To achieve a more flexible solution, QQmlListProperty can be employed. By implementing this property, the list model can be manipulated directly from QML, allowing for dynamic object insertion and removal.

Schema-less Models

The provided solutions assume models with a fixed schema. However, it's possible to create schema-less models using a QAbstractListModel that stores QObject* objects. This approach allows for objects with varying properties to be added to the model and accessed through meta information.

Implementing a Generic List Model

To implement a truly generic list model, the following example showcases a model that stores QObject* objects and provides various methods for managing and accessing the data:

class List : public QAbstractListModel {
    // ...
    Q_PROPERTY(QQmlListProperty<QObject> content READ content)
    // ...
};

This allows QML to interact with the list model's content dynamically, adding and removing objects as needed.

Using a Loader for Delegation

To handle varying object types, a Loader component can be utilized as a delegate, allowing for different QML UI implementations based on the object's properties.

Leveraging Sorting and Filtering Proxy

For added functionality, a simple sorting and filtering proxy can be implemented to enhance the usability of the generic model.

Conclusion

By utilizing the techniques described in this article, developers can create flexible and data-driven QML applications with generic object models that seamlessly interact with Qt models.

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