单击 kivy 按钮时如何调用 function？

Question

I'm pretty new to kivy. I want to call a function in the App class. But it gives an error. The error is "on_press: app.hello() TypeError: hello() takes 0 positional arguments but 1 was given"

.kv file code

            Button:
            id: add_income_btn
            size_hint: (.05, .2)
            pos: (393, 302)
            background_color: (1, 1, 1, 0)
            text: "+"
            font_size:'20sp'
            on_press: app.hello()

.py file code

Builder.load_file("test1.kv")
class Money_Manager(App,TabbedPanel): 
    def hello():
        print("Hello")

Answer 1

The methods of an instantiated Class in Python need a self argument (the current Class instance).
So you must use:

    def hello(self):
        print("Hello")

Answer 2

Try This One:

on_press: app.hello

instead of

on_press: app.hello()