Kivy ScrollView kullanımı

1 
<Button>:
    size_hint:1,.2
    background_color:(1,.1,0,1)
<MScreenManager>:
    Screen:
        name:"git"
        BoxLayout:
            size_hint:0.5,0.2
            pos_hint:{"center_y":0.9}
            orientation:"vertical"
            Button:
                text:"Giriş "
                on_press:app.basla("kelime")
    AScreen:
        name:"kelime"
     #   txt:txt
        container_y:container_y
        BoxLayout:
        	size_hint:.4,.2
            pos_hint:{'center_y':1}
            Button:
                text:"<<Geri"
                on_press:root.current="git"
        BoxLayout:
            padding:20
        	orientation:'vertical'
            ScrollView:
            	size_hint:.9,.9
            	do_scroll_y:1,None
            	BoxLayout:
            		TextInput:
            			id:container_y
            		   # size_hint_y:1,None
                	Button:
                		size_hint:.5,.5
                		text:'oku'
                    	on_press:app.ok()

#Böyle yaptım ama olmadı.
#Text içindeki metni aşağıya nasıl kaydırabilirim.