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.. _qml-chapter4-custompropertytypes:
Extending QML - Using Custom Property Types
===========================================
This is the fourth of a series of 6 examples forming a tutorial about extending
QML with Python.
The ``PieChart`` type currently has a string-type property and a color-type property.
It could have many other types of properties. For example, it could have an
int-type property to store an identifier for each chart:
.. code-block:: python
class PieChart(QQuickPaintedItem):
chartIdChanged = Signal()
@Property(int, notify=chartIdChanged)
def chartId(self):
pass
@chartId.setter
def setChartId(self, chartId):
pass
.. code-block:: javascript
// QML
PieChart {
...
chartId: 100
}
Aside from ``int``, we could use various other property types. Many of the Qt
data types such as ``QColor``, ``QSize`` and ``QRect`` are automatically
supported from QML.
If we want to create a property whose type is not supported by QML by default,
we need to register the type with the QML engine.
For example, let's replace the use of the ``property`` with a type called
``PieSlice`` that has a ``color`` property. Instead of assigning a color,
we assign an ``PieSlice`` value which itself contains a ``color``:
.. literalinclude:: app.qml
:lineno-start: 4
:lines: 4-22
Like ``PieChart``, this new ``PieSlice`` type inherits from
``QQuickPaintedItem``, is exposed via the ``QmlElement`` decorator and declares
its properties with the ``Property`` decorator:
.. literalinclude:: customPropertyTypes.py
:lineno-start: 21
:lines: 21-40
To use it in ``PieChart``, we modify the ``color`` property declaration
and associated method signatures:
.. literalinclude:: customPropertyTypes.py
:lineno-start: 58
:lines: 58-65
There is one thing to be aware of when implementing ``setPieSlice()``. The
``PieSlice`` is a visual item, so it must be set as a child of the ``PieChart``
using ``QQuickItem.setParentItem()`` so that the ``PieChart`` knows to paint
this child item when its contents are drawn.
As with ``PieChart``, we add the ``Charts`` type namespace, version 1.0:
.. literalinclude:: customPropertyTypes.py
:lineno-start: 15
:lines: 15-18
|
