Kivy/KivyMD：添加下拉项选择发生变化时的方法

Question

我使用 Kivy / KivyMD 和 Python 开发了一个 UI。 UI 非常简单：按下按钮时，DropDownItem 就会添加到布局中。我需要添加一个方法，每次 DropDownItem 的选择发生变化时都会调用该方法。这是代码：

from kivy.lang import Builder
from kivymd.app import MDApp
from kivymd.uix.screen import MDScreen
from kivymd.toast import toast
from kivymd.uix.menu import MDDropdownMenu
from kivymd.uix.dropdownitem.dropdownitem import MDDropDownItem
from kivy.metrics import dp



Builder.load_string(
    """    
<View>:
    MDGridLayout:
        rows: 3
        id: layout
        padding: 100, 50, 100, 50
        spacing: 0, 50
        
        
        MDRaisedButton:
            text: 'CREATE DDI'
            on_release: root.Button_CreateDDI__On_Click()
            
        MDRaisedButton:
            id: button_check
            disabled: True
            text: 'CHECK SELECTION'
            on_release: root.Button_CheckSelection_On_Click()       

""")



class View(MDScreen):
    def __init__(self, **kwargs):
        super(View, self).__init__(**kwargs)
        
        
    def Button_CreateDDI__On_Click(self):        
        self.myDdi = MDDropDownItem()
        self.myDdi.text = 'SELECT POSITION'
                
        myMenu, scratch = self.Create_DropDown_Widget(self.myDdi, ['POS 1', 'POS 2', 'POS 3'], width=4)
        self.myDdi.on_release = myMenu.open
        self.myDdi.bind(on_select = self.DDI_Selection_Changed)   
        
        
        self.ids.button_check.disabled = False
        self.ids.layout.add_widget(self.myDdi)
        
        
    def Button_CheckSelection_On_Click(self):
        toast('CURRENT VALUE: ' + self.myDdi.current_item)        
        
        
    def DDI_Selection_Changed(self):
        toast('SELECTION CHANGED: ' + self.myDdi.current_item)
        
       
    def Create_DropDown_Widget(self, drop_down_item, item_list, width):
        items_collection = [
            {
                "viewclass": "OneLineListItem",
                "text": item_list[i],
                "height": dp(56),
                "on_release": lambda x = item_list[i]: self.Set_DropDown_Item(drop_down_item, menu, x),
            } for i in range(len(item_list))
        ]
        
        menu = MDDropdownMenu(caller=drop_down_item, items=items_collection, width_mult=width)
        menu.bind()
        
        return menu, items_collection

         
    def Set_DropDown_Item(self, drop_down_item, menu, text_item):
        drop_down_item.set_item(text_item)
        menu.dismiss()
        
        
        

class MainApp(MDApp):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.View = View()


    def build(self):
        self.title = ' DROP DOWN ITEM ADDED DYNAMICALLY'
        return self.View


if __name__ == '__main__':
    MainApp().run()

当在kv部分添加DropDownItem时，可以使用select事件。一旦布局已经显示，就会在此处添加小部件。所以我尝试绑定 on_select 事件，但没有发生任何错误或异常。如何在每次 DropDownItem 的选择发生变化时调用方法？

Answer 1

您已经拥有一个每当选择下拉菜单中的项目时就会调用的函数。我会把吐司移到那里。

def Set_DropDown_Item(self, drop_down_item, menu, text_item):
    drop_down_item.set_item(text_item)
    menu.dismiss()

    toast('CURRENT VALUE: ' + text_item )