Property¶
Detailed Description¶
The Property function lets you declare properties that behave both as Qt and Python properties, and have their getters and setters defined as Python functions.
They are equivalent to the Q_PROPERTY
macro in the Qt Docs.
Here is an example that illustrates how to use this function:
1 from PySide2.QtCore import QObject, Property
2
3 class MyObject(QObject):
4 def __init__(self, startval=42):
5 QObject.__init__(self)
6 self.ppval = startval
7
8 def readPP(self):
9 return self.ppval
10
11 def setPP(self, val):
12 self.ppval = val
13
14 pp = Property(int, readPP, setPP)
15
16 obj = MyObject()
17 obj.pp = 47
18 print(obj.pp)
The full options for QtCore.Property
can be found with QtCore.Property.__doc__
:
Property(self, type: type,
fget: Optional[Callable] = None,
fset: Optional[Callable] = None,
freset: Optional[Callable] = None,
fdel: Optional[Callable] = None,
doc: str = '', notify: Optional[Callable] = None,
designable: bool = True, scriptable: bool = True,
stored: bool = True, user: bool = False,
constant: bool = False, final: bool = False) -> PySide2.QtCore.Property
Normally, only type
, fget``and ``fset
are used.
Properties compared with Python properties¶
Python
has property objects very similar to QtCore.Property
.
Despite the fact that the latter has an extra freset
function, the usage
of properties is almost the same. The main difference is that QtCore.Property
requires a type
parameter.
In the above example, the following lines would be equivalent properties:
pp = QtCore.Property(int, readPP, setPP) # PySide version
pp = property(readPP, setPP) # Python version
As you know from the Python Docs, Python
allows to break the property
creation into multiple steps, using the decorator syntax. We can do this in
PySide
as well:
1 from PySide2.QtCore import QObject, Property
2
3 class MyObject(QObject):
4 def __init__(self, startval=42):
5 QObject.__init__(self)
6 self.ppval = startval
7
8 @Property(int)
9 def pp(self):
10 return self.ppval
11
12 @pp.setter
13 def pp(self, val):
14 self.ppval = val
15
16 obj = MyObject()
17 obj.pp = 47
18 print(obj.pp)
Please be careful here: The two Python
functions have the same name, intentionally.
This is needed to let Python
know that these functions belong to the same property.
Properties in QML expressions¶
If you are using properties of your objects in QML expressions, QML requires that the property changes are notified. Here is an example illustrating how to do this:
1 from PySide2.QtCore import QObject, Signal, Property
2
3 class Person(QObject):
4 def __init__(self, name):
5 QObject.__init__(self)
6 self._person_name = name
7
8 def _name(self):
9 return self._person_name
10
11 @Signal
12 def name_changed(self):
13 pass
14
15 name = Property(str, _name, notify=name_changed)
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