class ActionBar(ActionBar):
    pass


class Manager(ScreenManager):
    pass


class Screen_one(Screen):
    pass


class Screen_two(Screen):
    pass


class GoodsView(ScrollView):
    def __init__(self, **kwargs):
        super(GoodsView, self).__init__(**kwargs)
        for i in range(10):
            self.ids.GoodsContainer.add_widget(Button(text="hi"))


class Screen_three(Screen):
    pass


class RandApp(App):
    def build(self):
        return Builder.load_file("pcapp.kv")


if __name__ == "__main__":
    RandApp().run()

BoxLayout:
    orientation: 'vertical'
    canvas.before:
        Color:
            rgba: .65, .75, .85, 1
        Rectangle:
            pos: self.pos
            size: self.size

    ActionBar: ...
    Manager:
        id: sm
        Screen_one:
            ...
        Screen_two:
            ...
        Screen_three:
            ...
<Screen_one>:
    FloatLayout:
        Button:
            text: "Click1"
            size_hint: .2, .05
            pos_hint: {'x': .2, 'y': .4}
            on_release:
                app.root.ids.sm.current  = 'screen2'
        Label:
            text: 'Hello!'
            pos_hint: {'x': -0.2, 'y': 0}

<Screen_two>:
    GoodsView:


<GoodsView>:
    id:gv
    do_scroll_x: False
    do_scroll_y: True
    size_hint_x: .7
    size_hint_y: .7
    pos_hint: {'x': .15,'y': .15}
    canvas.before:
        Color:
            rgba: 1, 0, 0, 1
        Rectangle:
            size: self.size
            pos: self.pos

    GridLayout:
        id: GoodsContainer
        row_force_default: True
        row_default_height: '50dp'
        cols: 1
        spacing: 10
        padding: 10