I use validators to filter user input. Normally I have my validators working like this:
my_reg_ex = QRegExp("[1-9]\d{0,5}")
my_validator = QRegExpValidator(my_reg_ex, self.ui.lineEdit_test)
self.ui.lineEdit_test.setValidator(my_validator)
I wrote this after looking at some examples online. But I just noticed that if I remove the last part on the second line:
, self.ui.lineEdit_test
The code works exactly the same. I have a couple of these validators all around. I was wondering if it's okay to just use it without the part I mentioned. For example:
my_reg_ex = QRegExp("[1-9]\d{0,5}")
my_validator = QRegExpValidator(my_reg_ex)
self.ui.lineEdit_test.setValidator(my_validator)
Is there any difference between these? If there is please explain and tell me which one is the better way to go.
The QRegExpValidator class inherits QObject, so its constructor has an argument that takes a parent QObject. One general reason for setting a parent, is to ensure the object doesn't get garbage-collected when it goes out of scope. This can easily happen if you don't keep any other reference to the object, and is a very common cause of many of the problems seen in newbie questions on SO.
However, this is actually not a problem in your specific example. This is because the line-edit takes ownership of the validator when you pass it to setValidator(), so you don't need to explicitly keep a reference to it yourself. As far as the code in your question is concerned, it really makes no difference whether you set a parent or not.
Having said that, there is at least one scenario where not setting a parent may be advantageous. This could arise if you needed to regularly reset the validator at runtime. If you gave each new validator a parent, the old one would not be deleted when setValidator() is called (because the parent would still hold a reference to it). So for the purposes of simplifying object-cleanup, not setting a parent in this situation might be preferrable.