在 Kivy 中动态构建下拉菜单

I'd like to create dropdown-lists in kivy based on a dictionary property of a class. But something about creating these in a loop is either confusing Kivy or I am just confused. Here's what I have:

for main, ingrediants in self.ingrediants.items():
    print main, ingrediants
    dropdown = DropDown()

    for ingrediant in ingrediants:
        btn = Button(text=ingrediant, size_hint_y=None, height=44)
        btn.bind(on_release=lambda btn: dropdown.select(btn.text))
        dropdown.add_widget(btn)

    trigger = Button(text=main, size_hint=(None, None))
    trigger.bind(on_release=dropdown.open)
    dropdown.bind(on_select=lambda instance, x: setattr(trigger, 'text', x))

    self.toolbar.dropdown_bar.add_widget(trigger)

这是我的财产的样子:

ingrediants = DictProperty(
    {
        'Milk': ['Whole Milk', 'Soy', 'Creamer'],
        'Coffee': ['Drip Coffee', 'Espresso', 'Pour Over'],
        'Sugar': ['Sugar', 'Simple Syrup', 'Raw Sugar'],
    }
)

当这个渲染时，下拉栏看起来是正确的，三个按钮，但是，牛奶一个没有触发下拉目，咖啡一个触发它的下拉次，但选择时，改变糖按钮的文本，第三个按钮正常工作，触发下拉菜单并在选择时更改按钮文本.

dropdowns = {}
for main, ingrediants in self.ingrediants.iteritems():
    dropdowns[main] = DropDown()

    for ingrediant in ingrediants:
        btn = Button(text=ingrediant, size_hint_y=None, height=44)
        btn.bind(on_release=lambda btn=btn, dropdown=dropdowns[main]: dropdown.select(btn.text))
        dropdowns[main].add_widget(btn)

    trigger = Button(text=main, size_hint=(None, 1))

    trigger.bind(on_release=dropdowns[main].open)
    dropdowns[main].bind(on_select=lambda instance, x, trigger=trigger: setattr(trigger, 'text', x))
    self.toolbar.dropdown_bar.add_widget(trigger)