QSignalTransition 子类从未收到自定义 PyQt 信号

Question

Trying to learn PyQt5 QStateMachine with transitions derived from QSignalTransition following this example written for PySide. To use PyQt I just changed the definition of the signal, and the way it is referenced in QSignalTransition initializer. This is the complete code:

from PyQt5.QtCore import QObject, pyqtSignal, QSignalTransition, QCoreApplication, QStateMachine, QState, QFinalState


class Factorial(QObject):
    xChanged = pyqtSignal(int)
    def __init__(self):
        super(Factorial, self).__init__()
        self.xval = -1
        self.facval = 1
    def getX(self):
        return self.xval
    def setX(self, x):
        if self.xval == x:
            return
        self.xval = x
        self.xChanged.emit(x)
    x = property(int, getX, setX)
    def getFact(self):
        return self.facval
    def setFact(self, fac):
        self.facval = fac
    fac = property(int, getFact, setFact)

class FactorialLoopTransition(QSignalTransition):
    def __init__(self, fact):
        super(FactorialLoopTransition, self).__init__(fact.xChanged[int])
        self.fact = fact
    def eventTest(self, e):
        if not super(FactorialLoopTransition, self).eventTest(e):
            return False
        return e.arguments()[0] > 1
    def onTransition(self, e):
        x = e.arguments()[0]
        fac = self.fact.fac
        self.fact.fac = x * fac
        self.fact.x = x - 1

class FactorialDoneTransition(QSignalTransition):
    def __init__(self, fact):
        super(FactorialDoneTransition, self).__init__(fact.xChanged[int])
        self.fact = fact
    def eventTest(self, e):
        if not super(FactorialDoneTransition, self).eventTest(e):
            return False
        return e.arguments()[0] <= 1
    def onTransition(self, e):
        print(self.fact.fac)

if __name__ == '__main__':
    import sys
    app = QCoreApplication(sys.argv)
    factorial = Factorial()
    machine = QStateMachine()

    compute = QState(machine)
    compute.assignProperty(factorial, 'fac', 1)
    compute.assignProperty(factorial, 'x', 6)
    compute.addTransition(FactorialLoopTransition(factorial))

    done = QFinalState(machine)
    doneTransition = FactorialDoneTransition(factorial)
    doneTransition.setTargetState(done)
    compute.addTransition(doneTransition)

    machine.setInitialState(compute)
    machine.finished.connect(app.quit)
    machine.start()
    sys.exit(app.exec_())

This state machine just compute the factorial of 6 and print it.

My problem is, in both transitions, this piece of code:

def eventTest(self, e):
    if not super(FactorialDoneTransition, self).eventTest(e):
        return False
    return e.arguments()[0] <= 1

returns False on the first and only call. I assume this is because the event passed is not of the proper type, and the superclass returns False . With this behavior the transitions are never executed, and the the state machine remains at its initial state.

Can someone explain what is the problem? Is it my conversion from PySide to PyQt which is wrong?

Answer 1

The assignProperty() method expects a Q_PROPERTY that in the case of PySide/PySide2 equals Property (which is different from the property provided by python natively) and in the case of PyQt4/PyQt5 you must use pyqtProperty , and that is the cause of the error so the solution is to replace with the following:

from PyQt5.QtCore import QObject, pyqtSignal, QSignalTransition, QCoreApplication, QStateMachine, QState, QFinalState, pyqtProperty


class Factorial(QObject):
    xChanged = pyqtSignal(int)
    def __init__(self):
        super(Factorial, self).__init__()
        self.xval = -1
        self.facval = 1

    def getX(self):
        return self.xval

    def setX(self, x):
        if self.xval == x:
            return
        self.xval = x
        self.xChanged.emit(x)

    x = pyqtProperty(int, getX, setX) # <---

    def getFact(self):
        return self.facval

    def setFact(self, fac):
        self.facval = fac

    fac = pyqtProperty(int, getFact, setFact) # <---

# ...