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

How to Define a Generic Object Model for QML Usage

Introduction

QML applications often require flexible and data-driven models to display and manipulate information. This article explores a method for creating a generic object model that can be used seamlessly within QML.

Creating a Generic Object Model

Yes, it is possible to define a property of type AnimalModel * within a QObject in QML. This can be accomplished with the Q_PROPERTY macro:

class DataObject : public QObject
{
    Q_OBJECT
    
    Q_PROPERTY(AnimalModel * modelAnimals READ modelAnimals)
    ...
};

However, it's worth noting that:

• The model reference will be a pointer, not a direct instance of AnimalModel.
• QML will automatically reflect changes within the model without the need for a NOTIFY signal.
• Setting the entire model (replacing it) should be done through a slot or Q_INVOKABLE instead of a property setter.

Dynamic Model Approach

For greater flexibility, consider creating a model that stores QObject * objects instead of specific model types. This allows for adding objects with arbitrary properties to the model. The following code demonstrates such a model:

class List : public QAbstractListModel
{
    Q_OBJECT
    
    QList<QObject *> _data;
    
    ...
    
    // Proxy model for sorting and filtering
    SortingAndFilteringProxy * m_proxyModel;
    
    ...
};

This model can be registered with QML and utilized as a generic model for managing objects of various types.

QML Usage and Delegate Loading

In QML, the generic model can be used as the data source for views. To render different delegates based on object types, a Loader can be used:

Loader {
    sourceComponent: Qt.createComponent(obj.objectName + ".qml")
}

The objectName property or another property can be leveraged to determine the appropriate delegate to load.

Dynamic Sorting and Filtering

The generic model can be further enhanced by implementing a sorting and filtering proxy model:

class SortingAndFilteringProxy : public QSortFilterProxyModel
{
    Q_OBJECT
    
    ...
};

This proxy model can be set as a data source for the generic model to enable dynamic sorting and filtering of objects based on properties or other criteria.

Conclusion

Defining a generic object model in QML allows for flexibility and dynamic handling of data. Using a QObject-based model and QML's meta-object system enables seamless integration with various object types and facilitates the creation of flexible and adaptive QML applications.

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