[QScintilla] Mouse event filter for QsciScintilla

[VA]

Le 13/11/2017 à 23:15, Phil Thompson a écrit :
> On 13 Nov 2017, at 8:02 pm, VA <dev+pyqt at indigo.re> wrote:
>>
>> Le 13/11/2017 à 20:35, Phil Thompson a écrit :
>>> On 13/11/2017 18:41, VA wrote:
>>>> Le 13/11/2017 à 15:49, Phil Thompson a écrit :
>>>>> They do receive mouse press events. They are consumed (ie. accepted) and so do not make it to the event filter.
>>>>
>>>> Why don't they pass through the event filter as other events?
>>> That’s the way Qt works. If a mouse or key event is ignored (rather than accepted) then it will be passed to the filter.
>>
>> It's the opposite in Qt, the event filter is tested first, and if the filter returns true, the event will not even reach the widget.
>> See the reference doc:
>> https://doc.qt.io/qt-5/qobject.html#installEventFilter
>>
>> And test this code where no text can be typed in a QtWidgets.QTextEdit (and no mouse clicks) because an event filter filters events before the QTextEdit receives them:
>>
>> class Filter(QObject):
>> 	def eventFilter(self, target, ev):
>> 		return True
>>
>> app = QApplication([])
>> f = Filter()
>> sci = QTextEdit()
>> sci.installEventFilter(f)
>> sci.show()
>> app.exec_()
>>
>> So the events (like mouse press) sent to QsciScintilla should always go through the event filter first, and if the filter returns true, the QsciScintilla should not receive the event.
> 
> So how do you explain the the behaviour of the attached?

Well, I added a print in your sample code in the event() method, and it 
seems with QsciScintilla, event() is called before eventFilter(), as you 
say.
However, if I replace QsciScintilla with a QLineEdit or a QPushButton, 
eventFilter() is called before event(), so it cannot depend on 
QEvent.ignore() being called with QLineEdit or QPushButton, since 
ignore() has not been called yet. Additionaly, returning True in 
eventFilter() prevents event() from being reached.
My opinion is that QLineEdit or QPushButton have the right behavior (at 
least, it's consistent with the QObject docs I linked to earlier)

Reading QCoreApplication::notify_helper 
(https://code.woboq.org/qt5/qtbase/src/corelib/kernel/qcoreapplication.cpp.html#1159) 
seems to confirm that event filters should be called before delivering 
an event to an object.