有人可以告诉我这种结构在哪里出错吗？

Question

I'm trying to call a function from my .kv but I cannot find the correct way to reference a function outside the function that draws the widgets. I've tried root.dostuff parent... self... MyApp... App... I could put the function into the Widgets class, but that breaks other stuff...

MyApp.py

class Widgets(Widget):
    pass

def dostuff(x):
    print(x)

class MyApp(App):
    def build(self):
        global w
        print("Build")
        w = Widgets()
        return w

if __name__ == "__main__":
    MyApp().run()

MyApp.kv:

Button:
    text: "Press Me"
    on_press: dostuff(1)

Answer 1

You have two problems. The first is that the function dostuff isn't defined in the kv file. You can import it with #:import dostuff MyApp.dostuff or make it a method of eg the app class and call it with app.dostuff() .

Also, your kv file isn't actually loaded. To have it be loaded and you don't display the button it would produce, so your example wouldn't actually demonstrate your problem. Name the file my.kv to have it loaded automatically, and don't return anything from the build methd to have your Button used as the root widget.

Answer 2

the correct way to reference a function outside the function that draws the widgets.

You can also define on_press() outside the kv file :

from kivy.uix.button import Button
from kivy.app import App

def dostuff(x):
    print("x is %s" % x)


class MyButton(Button):
    def on_press(self):
        dostuff(22)

class MyApp(App):

    def build(self):
        return MyButton()

MyApp().run()

my.kv:

<MyButton>:
    text: "Press Me"

Or, with on_press() inside the kv file :

my.kv:

<MyButton>:
    text: "Press Me"
    on_press: self.dostuff(10, 20)  #Look in MyButton class for dostuff()

---

...
...

class MyButton(Button):
    def dostuff(self, *args):
        print(args)

...
...

I've tried root.dostuff parent... self... MyApp... App.

Here's how root and app work in a kv file:

my.kv:

<MyWidget>: #This class is the 'root' of the following widget hierarchy:
    Button:
        text: "Press Me"
        on_press: root.dostuff(20, 'hello') #Look in the MyWidget class for dostuff()
        size: root.size  #fill MyWidget with the Button

---

from kivy.uix.widget import Widget
from kivy.app import App

class MyWidget(Widget):
    def dostuff(self, *args):
        print(args)

class MyApp(App):

    def build(self):
        return MyWidget()

MyApp().run()

Or, you can put the function inside the App class :

my.kv:

<MyButton>:
    text: "Press Me"
    on_press: app.dostuff('hello', 22)

---

from kivy.app import App
from kivy.uix.button import Button

class MyButton(Button):
    pass

class MyApp(App):
    def dostuff(self, *args):
        print(args)

    def build(self):
        return MyButton()

MyApp().run()

I could put the function into the Widgets class, but that breaks other stuff...

Well, don't let the function do that.