kivy Property Difference between Properties and Binding.


Example

In brief:

  • Properties make it easy to pass updates from the python side to the user interface
  • Binding passes the changes that happened on the user interface to the python side.
from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.lang import Builder
from kivy.properties import StringProperty
from kivy.properties import ObjectProperty
from kivy.uix.textinput import TextInput
from kivy.event import EventDispatcher
Builder.load_string("""
<CustLab1@Label>
    size_hint:0.3,1
<CustLab2@Label>
    text: "Result"
    size_hint: 0.5,1
<CustButton@Button>
    text: "+1"
    size_hint: 0.1,1    
<CustTextInput@TextInput>:
    multiline: False
    size_hint:0.1,1
    
<Tuto_Property>:
    orientation: "vertical"
    padding:10,10
    spacing: 10
    Label:
        text: "Press the 3 button (+1) several times and then modify the number in the TextInput.The first counter (with StringProperty but no binding) doesn't take into account the change that happened in the app, but the second one does.String Property makes it easy to pass the update from the python side to the user interface, binding pass the changes that happened on the user interface to the python side. "
        text_size: self.size
        padding: 20,20
        
    Property_no_Binding:
    Property_with_Binding:
    Simple:

<Property_no_Binding>:
    spacing: 10
    label_ObjectProperty: result
    CustLab1:
        text: "With Property but no Binding"
    CustButton:
        on_press: root.counter_textInput_StringProperty()
    CustTextInput:
        id:textinput_id
        text: root.textInput_StringProperty
    CustLab2:
        id: result    
        
<Property_with_Binding>:
    spacing: 10
    label_ObjectProperty: result
    CustLab1:
        text: "With Property and Binding"
    CustButton:
        on_press: root.counter_textInput_StringProperty()
    CustTextInput:
        id:textinput_id
        text: root.textInput_StringProperty
        on_text: root.textInput_StringProperty = self.text   ## this is the binding 
    CustLab2:
        id: result
        
<Simple>
    spacing: 10
    CustLab1:
        text: "Without Property"
    CustButton:
        on_press: root.simple(textinput_id, result)
    CustTextInput:
        id:textinput_id
        text: "0"
    CustLab2:
        id: result


        
""")

class Property_no_Binding(BoxLayout):
    textInput_StringProperty= StringProperty("0")
    label_ObjectProperty = ObjectProperty(None)
    def counter_textInput_StringProperty(self):
        self.label_ObjectProperty.text= ("Before the counter was updated:\n\n textinput_id.text:" + self.ids.textinput_id.text + "\n\n textInput_StringProperty:" + self.textInput_StringProperty)
        self.textInput_StringProperty =str(int(self.textInput_StringProperty)+1)     
        
class Property_with_Binding(BoxLayout):
    textInput_StringProperty= StringProperty("0")
    label_ObjectProperty = ObjectProperty(None)
    def counter_textInput_StringProperty(self):
        self.label_ObjectProperty.text= ("Before the counter was updated:\n\n textinput_id.text:" + self.ids.textinput_id.text + "\n\n textInput_StringProperty:" + self.textInput_StringProperty)
        self.textInput_StringProperty =str(int(self.textInput_StringProperty)+1)     
    pass
    
class Simple(BoxLayout):
    def simple(self,textinput_id, result):
        result.text = ("Before the counter was updated:\n\nIn the TextInput:" + textinput_id.text)
        textinput_id.text = str(int(textinput_id.text) + 1)
        pass
class Tuto_Property(BoxLayout): 

    
    # def __init__(self, **kwargs):
        # super(All, self).__init__(**kwargs)
        # app=App.get_running_app()
        # self.objproper_number.bind(text=lambda *a: self.change(app))
        # print(self.parent)
        
    # def counter(self,app): 
        # print("Stringproperty:",app.numbertext) 
        # print("ObjectProperty:",self.objproper_number.text)
        # print("text:",self.ids.number.text,"\n")
        # app.numbertext=str(int(app.numbertext)+1)

    # def change(self, app):
        # app.numbertext=self.objproper_number.text
    pass
class MyApp(App):
    numbertext = StringProperty("0")
    def build(self):       
        return Tuto_Property()


MyApp().run()