When trying to work with Qt's signal/slot mechanisms over more than one level of inheritance, I ran into a problem: When my class does not directly inherit from QObject, signals and slots don't seem to work any more.
The output of the following program illustrates the case:
require 'Qt'
class A < Qt::Object
signals 'mySignal()'
slots 'mySlot()'
def initialize
super()
puts "This is the c'tor of A and I am a #{self.class}"
connect(self, SIGNAL('mySignal()'), self, SLOT('mySlot()'))
emit mySignal()
end
def mySlot
puts "Signal received and I am a #{self.class}"
end
end
class B < A
def initialize
super()
end
end
app = Qt::Application.new(ARGV)
A.new
B.new
app.exec
The program yields
This is the c'tor of A and I am a A Signal received and I am a A This is the c'tor of A and I am a B
However, I would expect
This is the c'tor of A and I am a A Signal received and I am a A This is the c'tor of A and I am a B Signal received and I am a B
Qt' documentation states, that it "[...] assumes that the first inherited class is a subclass of QObject.". Since B < A < QObject, I would expect that to be true. The according C++ program behaves as expected (although you cannot identify the type of an object in its c'tor in c++, but that is besides the point here).
The question is: Why does the program not give the expected output?
