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:
- Create a QAbstractListModel or QObject model that stores QObject .
- Provide a single object role that returns the object.
- Use a Loader as a delegate to instantiate different QML UI implementations based on the object type.
- 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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