如何在 Kivy 中使用 NumericProperty()？

Question

I am trying to get a value from the .kv file to the Python file as follows:

Python:

class Calc(Widget):    
    def func(self):

        alp = NumericProperty()
        bet = NumericProperty()

        some calculation ... alp + bet

Kivy:

<Calc>

 alp: alpha.text
 bet: beta.text

 TextInput:
     id: alpha
 TextInput:
     id: beta

I have tried different things (eg converting the string to float, int, etc) nothing seems to work. I tried using "alp: alpha", and that does not seem to work either.

What am I doing wrong?

Thank you!

---

Revision 1

Python:

class Calc(Widget):    

    alp = NumericProperty()
    bet = NumericProperty()

    def func(self):

        some calculation ... alp + bet

Kivy:

<Calc>

    alp: alpha.text
    bet: beta.text

    TextInput:
        id: alpha
    TextInput:
        id: beta

So, it is still not working - because eg alpha.text returns a string to alp = NumericProperty(). As far as I know, ".text" is the only attribute that returns the content of the InputLabel. Any ideas? Thank you.

---

Revision 2

It seems like I have solved the problem by using ObjectProperty().

Python:

class Calc(Widget):    
def func(self):

    alp = ObjectProperty('float')
    bet = ObjectProperty('float')

    some calculation ... alp + bet

I also applied the filters 'float' but I do not think they are doing anything. Does anyone know how to set up a nice Error Handler if the user inputs other than numeric values?

Answer 1

Kivy properties must be declared at the class level. Check out this part of the tutorial: http://kivy.org/docs/gettingstarted/properties.html

That means you should have something like

class Calc(Widget):

    alp = NumericProperty()
    bet = NumericProperty()

    def func(self):
        some calculation ... alp + bet

Answer 2

if your aim is to get input from Text_Input access text attribute and cast them to float or int and add them and display the result, below code should help

class Calc(Widget):    
   alp = ObjectProperty()
   bet = ObjectProperty()

   def func(self):          
      #some calculation ... alp + bet
      add = float(self.alp.text)+ float(self.bet.text)
      #print add to cmd prompt
      print(add)

this might help :)

Answer 3

用这个：

from kivy.properties import *