为什么不叫kivy中的"on_< propname>"? [英] Why ‘on_<propname>’ in kivy is not called?

问题描述

在kivy文档(1.9.0-dev)中，它说

in the kivy document (1.9.0-dev), it says

使用"on_<propname>"观察如果您自己创建了该类， 可以使用"on_<propname>"回调:

Observe using ‘on_<propname>’ If you created the class yourself, you can use the ‘on_<propname>’ callback:

class MyClass(EventDispatcher):
   a = NumericProperty(1) 

   def on_a(self, instance, value): 
      print(’My property a changed to’, value)

我的代码是

class MyClass(EventDispatcher):
    a = StringProperty('')
    def __init__(self, **kwargs):  

    ...

        self.bind(a=self.on_a)    <--- if I remove this

    def on_a(self, instance, value): 
      print(’My property a changed to’, value) 

这有效.但是，如果我删除self.bind(a = self.on_a)

This works. But if I remove self.bind(a=self.on_a)

然后不调用on_a函数.我以为如果我把on_作为函数名，那么我就不需要做bind()了.我想念什么吗?

Then on_a function is not called. I thought if I put on_ as a function name then I do not need to do bind(). Do I miss something?

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Ps.我在下面简化了我的代码.这是一个完全可运行的代码.

Ps. I simplified my code below. It is a full run-able code.

course_view.py:

course_view.py:

from kivy.app import App

from kivy.properties import StringProperty
from kivy.event import EventDispatcher
from kivy.uix.listview import ListView, ListItemButton
from kivy.adapters.dictadapter import DictAdapter
from kivy.uix.boxlayout import BoxLayout


from kivy.factory import Factory
from kivy.uix.screenmanager import ScreenManager, Screen, FadeTransition

from kivy.properties import ObjectProperty
from kivy.properties import StringProperty

class ChangeTest(App):
    pass

class StartScreen(Screen):
    pass

    def load_view(self):
       self.course_view_object = CourseCnDetailListView(view_box = self.ids.view_box) 
       self.clear_widgets()
       self.add_widget(self.course_view_object.master_item_list)


class CourseCnDetailListView(EventDispatcher):
    course_code = StringProperty('course_code_str')    
    def __init__(self, **kwargs):        

        self.view_box = kwargs.get('view_box', None)  
        self.course_data= {"1": {"course_code": "it123"},
                            "2": {"course_code": "it456"}
                           }
        list_item_args_converter = \
                lambda row_index, rec: {'text': rec["course_code"],
                                        'size_hint_y': None,
                                        'height': 25}

        dict_adapter = DictAdapter(sorted_keys=sorted(self.course_data.keys()),
                                   data=self.course_data,
                                   args_converter=list_item_args_converter,
                                   selection_mode='single',
                                   allow_empty_selection=False,
                                   cls=ListItemButton)
        self.master_item_list = ListView(adapter=dict_adapter,
                                    size_hint=(.3, 1.0))
        dict_adapter.bind(on_selection_change=self.course_changed)
        #self.bind(course_code=self.on_course_code)  <-- un-comment this will work
    def on_course_code(self, instance, value):
        print "on_course_code: update string value:", value  
    def redraw(self, *args):
        pass
    def course_changed(self, list_adapter, *args):        

            if len(list_adapter.selection) != 0:
                selection = list_adapter.selection[0] 
                if type(selection) is str:
                    self.course_code = selection
                else:
                    self.course_code = selection.text 

                self.redraw()


ChangeTest().run()            
Factory.register('StartScreen', cls=StartScreen)

ChangeTest.kv

ChangeTest.kv

#: kivy 1.9
#: import ScreenManager kivy.uix.screenmanager.ScreenManager
#: import Screen kivy.uix.screenmanager.ScreenManager



ScreenManager:
    id: screen_manager
    StartScreen:
        id: start_screen
        name: 'StartScreen'
        manager: screen_manager


<StartScreen>:
    BoxLayout:
        id: view_box
        Button:
            text: "load view"
            on_release: root.load_view()

推荐答案

谢谢zeeMonkeez.

Thank you zeeMonkeez.

是的.那正是问题所在.添加构造函数super(CourseCnDetailListView, self).__init__(**kwargs)之后.效果很好.

Yes. That is exactly the problem. After I add the constructor super(CourseCnDetailListView, self).__init__(**kwargs). It works perfectly.

当我更改结构时，它被意外删除.非常感谢.

It was accidentally removed when I changed the structure. Thank you very much.

也很高兴知道它是EventDispatcher使<on_propname>工作的默认构造函数.

Also it is good to know that it is the default constructor of EventDispatcher make <on_propname> work.

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