NumericProperty wont update

Question

I am trying to update the position of a widget via a NumericProperty. I have it updated in a function. When the function has been called the NumericProperty wont update

main.py

class Game(Screen):
    x = 0
    y = 0
    x_value = NumericProperty(x)
    y_value = NumericProperty(y)

    def update(self):
        self.x = self.x + 20
        self.y = self.y + 30

main.kv

Game:
    FloatLayout:
        Button:
            text: "higher"
            pos: (root.x_value + root.y_value)
            on_release: root.update()

The Button stays at the same position. What can I do?

Answer 1

Your NumericProperty definitions are equivalent to x_value = NumericProperty(0), they don't know anything about the fact that the argument passed to them was named x in the local namespace. It looks like you expect updating self.x later will affect the NumericProperty, but this is not the case.

You can instead directly write self.x_value = self.x_value + 20 without reference to the initial-value variable. This should do what you want.