Kivy中如何正确向Popup传递函数实现按钮触发？

问题根源 #

你的代码存在两个关键错误导致异常行为：

1. 立即执行函数而非保存引用：在MainScreenButton2方法中，self.popupMethod = self.method_2()这行代码里，method_2()会直接调用函数并将返回值（此处为None）赋值给popupMethod，因此打开Popup-2时method_2就会提前执行。
2. KV语言中未触发方法调用：Popup-2的Action-2按钮里app.popupMethod仅访问变量，没有执行方法调用操作。

快速修复方案 #

只需修改两处代码即可解决问题：

1. 调整MainScreenButton2方法的赋值逻辑：
   去掉函数后的括号，保存函数对象而非执行结果：

   def MainScreenButton2(self):    # opens popup-2
       # set the text of the popup
       self.Popup2Button1 = "Action-2"
       self.Popup2Button2 = "Dismiss"
       self.Popup2Title = "Title of Popup-2"
       self.Popup2Label = "Label of Popup-2"
       self.popupMethod = self.method_2  # 去掉括号，保存函数引用
       # set the popup structure
       self.popupMessage = Popup2(self)
       self.popupMessage.open()
   

2. 修改KV语言中Popup2的按钮绑定：
   在app.popupMethod后添加括号，触发方法执行：

   <Popup2>:
       size_hint: 1, 1
       auto_dismiss: False
       title: app.Popup2Title       
       title_align: "center"
       title_size: 30
       BoxLayout:
           orientation: "vertical"
           Label:
               font_size: '30sp'
               text: app.Popup2Label
           BoxLayout:
               orientation: "horizontal"
               spacing: 10
               size_hint: 1, 0.5
               Button:
                   font_size: 50
                   text: app.Popup2Button1
                   on_press:
                       app.popupMethod()  # 添加括号调用方法
                       root.dismiss()
               Button:
                   font_size: 50
                   text: app.Popup2Button2
                   on_press:
                       app.cancel()
                       root.dismiss()
   

更优雅的优化方案（推荐） #

通过给Popup2添加属性传递回调方法，避免依赖App实例的变量，提升代码解耦性：

1. 修改Popup2类：添加ObjectProperty用于接收回调方法

   # popup class
   class Popup2(Popup):
       callback = ObjectProperty(None)  # 添加回调属性
       def __init__(self, obj, **kwargs):
           super(Popup2, self).__init__(**kwargs)
           self.obj = obj
   

2. 调整MainScreenButton2方法：创建Popup2时直接传递回调方法

   def MainScreenButton2(self):    # opens popup-2
       # set the text of the popup
       self.Popup2Button1 = "Action-2"
       self.Popup2Button2 = "Dismiss"
       self.Popup2Title = "Title of Popup-2"
       self.Popup2Label = "Label of Popup-2"
       # set the popup structure，传递回调方法
       self.popupMessage = Popup2(self, callback=self.method_2)
       self.popupMessage.open()
   

3. 修改KV语言中Popup2的按钮绑定：使用root.callback调用方法

   <Popup2>:
       size_hint: 1, 1
       auto_dismiss: False
       title: app.Popup2Title       
       title_align: "center"
       title_size: 30
       BoxLayout:
           orientation: "vertical"
           Label:
               font_size: '30sp'
               text: app.Popup2Label
           BoxLayout:
               orientation: "horizontal"
               spacing: 10
               size_hint: 1, 0.5
               Button:
                   font_size: 50
                   text: app.Popup2Button1
                   on_press:
                       root.callback()  # 使用Popup实例的回调属性
                       root.dismiss()
               Button:
                   font_size: 50
                   text: app.Popup2Button2
                   on_press:
                       app.cancel()
                       root.dismiss()
   

修改完成后，Popup-2的行为会和Popup-1完全一致：点击Action-2按钮时才执行method_2，打开Popup时不会提前触发方法。

内容的提问来源于stack exchange，提问作者parovelb