[PyQt] Use pyqtProperty on QObject instance

[Kyle Altendorf]

When do you figure out what the properties should be and when do you need to create the class?  You can dynamically create classes with three-arg type() calls.

I went another approach for my needs with signals.  A simplified explanation of the idea is that instead of adding signals dynamical to a class you can instead add other QObject instances with signals on them as attributes of your primary class.  I wrapped this up with a descriptor which I can use pretty much as a drop in replacement for pyqtSignal but without having to inherit from QObject.  Not sure if that approach ends up helpful here though.  Of course there is overhead associated with extra objects etc but... sometimes that doesn't matter.

https://github.com/altendky/stlib/blob/f779e9c4d5ca4015eafe946b3281a9dcdd7a9fd9/epyqlib/utils/qt.py#L1172-L1210

Cheers,
-kyle

On May 27, 2019 2:38:04 PM EDT, Patrick Stinson <patrickkidd at gmail.com> wrote:
>So they are. I wonder if this can be done with attached properties.
>
>> On May 27, 2019, at 9:59 AM, Phil Thompson
><phil at riverbankcomputing.com> wrote:
>> 
>>> On 27/05/2019 17:41, Patrick Stinson wrote:
>>> Ok, that answers my question. I will figure out a way to add the
>>> properties to the class the first time they are added to one of the
>>> instances. They are always the same, after all.
>> 
>> Properties (like signals) are part of the class *definition* (as far
>as Qt is concerned). You can't add them dynamically.
>> 
>> Phil
>> 
>>>>> On May 27, 2019, at 9:11 AM, Phil Thompson
><phil at riverbankcomputing.com> wrote:
>>>>> On 27/05/2019 16:33, Patrick Stinson wrote:
>>>>> I have a custom object property system that adds properties to
>QObject
>>>>> instances and am trying to expose those [dynamic] properties to
>qml.
>>>>> Is it possible to add a qt property to a QObject instance, as
>opposed
>>>>> to adding it using pyqtProperty as a decorator in the class
>>>>> declaration?
>>>>> The PyQt5 docs say that you can use pyqtProperty in the same way
>as
>>>>> the python property() function apart from the decorator, but I
>haven’t
>>>>> had much success with this:
>>>>> def test_property():
>>>>>   class A(QObject):
>>>>>       def __init__(self):
>>>>>           self._mine = 12
>>>>>           self.mine = pyqtProperty(int, self.get_mine,
>self.set_mine)
>>>>>       def get_mine(self):
>>>>>           return self._mine
>>>>>       def set_mine(self, x):
>>>>>           self._mine = x
>>>>>   a = A()
>>>>>   print(a.mine)
>>>>>   print(a.mine())
>>>>> turin:pkdiagram patrick$ python test.py
>>>>> <PyQt5.QtCore.pyqtProperty object at 0x114ea1840>
>>>>> Traceback (most recent call last):
>>>>> File "test.py", line 743, in <module>
>>>>>   test_property()
>>>>> File "test.py", line 740, in test_property
>>>>>   print(a.mine())
>>>>> TypeError: Required argument 'fget' (pos 1) not found
>>>>> turin:pkdiagram patrick$
>>>> Properties are class objects not instance objects.
>>>> Phil
>> 
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