How do I determine what direction a QSlider is being moved?

Question

Is there a way to get the direction that a QSlider in Qt 5.9 is moving?

For context, I am making a GUI in which the user can adjust some sliders, under the condition that the total sum is below 1.

The sliders are above each other, and if you move one of the lower slider, those above does not move. Those below, however, do.

For the last slider, the user should not be able to move it upward, but should be allowed to move it downward.

In advance, thanks :)

I guess you can simply save the last slider value to calculate the direction. I don't think the slider itself does that for you and you only get the new value, no delta or something. — xander, Sep 28 '17 at 12:42
If current value is greater than previous one - slider moved forward and backward otherwise. — vahancho, Sep 28 '17 at 12:44

score 1 · Accepted Answer · answered Sep 28 '17 at 14:31

QSlider does not have that property, so the most reasonable thing is to create a class using the logic of having stored the previous position, in the following class I have implemented this logic, I have also added a signal to notify you asynchronously:

class Slider(QSlider):
    Nothing, Forward, Backward = range(3)
    directionChanged = pyqtSignal(int)
    def __init__(self, parent=None):
        QSlider.__init__(self, parent)
        self._direction = Slider.Nothing
        self.last = self.value()/self.maximum()
        self.valueChanged.connect(self.onValueChanged)

    def onValueChanged(self, value):
        current = value/self.maximum()
        direction = Slider.Forward if self.last < current else Slider.Backward
        if self._direction != direction:
            self.directionChanged.emit(direction)
            self._direction = direction
        self.last = current

    def direction(self):
        return self._direction

In the following part there is an example of the use of this class:

class Widget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setLayout(QVBoxLayout())
        slider = Slider(self)
        slider.setOrientation(Qt.Horizontal)
        self.layout().addWidget(slider)
        slider.directionChanged.connect(self.onDirectionChanged)
        slider.valueChanged.connect(self.onValueChanged)

    def onDirectionChanged(self, direction):
        if direction == Slider.Forward:
            print("Forward")
        elif direction == Slider.Backward:
            print("Backward")

    def onValueChanged(self, value):
        dirstr = "Forward" if self.sender().direction() == Slider.Forward else "Backward"
        print(value, dirstr)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    w = Widget()
    w.show()
    sys.exit(app.exec_())

How do I determine what direction a QSlider is being moved?

1 Answers1