如何像 Kivy 中的 CSS 一样按类名选择小部件？

Question

For example I want to put a background color to all the buttons in the application :

<Layout1>:
    <BoxLayout>:
        <Button>:
            text: "btn 1"
        <Button>:
            text: "btn 2"
        <Button>:
            text: "btn 3"
    <Button>:
        text: "Another button outside the boxlayout"

<Layout2>:
    <GridLayout>:
        cols: 2
        <Button>:
            text: "btn 1 in a grid"
        <Button>:
            text: "btn 2 in a grid"

But I don't want to do that by hand for all of them like this :

...
    <Button>:
        text: "btn 1"
        background_color: (1, 0, 0, 1)
    <Button>:
        text: "btn 2"
        background_color: (1, 0, 0, 1)
    <Button>:
        text: "btn 3"
        background_color: (1, 0, 0, 1)
...

So I'm looking for a shorter way like if we can put a class like in CSS to all of the buttons and access them by the class name. Something like that :

...
    <Button>:
        text: "btn 1"
        class: "btn_class"
    <Button>:
        text: "btn 2"
        class: "btn_class"
    <Button>:
        text: "btn 3"
        class: "btn_class"
...

And in python code :

for btn in get_widgets_by_classname("btn_class") :
    btn.background_color = (1, 0, 0, 1)

In the documentation https://kivy.org/doc/stable/api-kivy.lang.html#overview it says :

You can target a specific class of widgets (similar to the CSS concept of a class) by using the cls attribute (eg cls=MyTestWidget)

but it's not that clear for me about the use of the cls attribute.

Answer 1

Good day. In kvlang, you have two options for creating template widgets.

1. Create a Custom Widget:

Custom Widgets allows you to create a new, defined widget.

<CustomButton@Button>:
    background_color: (1,0,0,1)

Then use the button wherever you want with the following syntax. CustomButton:

2. Use rules:

At the start of the script, assign properties to a widget using the following syntax.

<Button>:
    background_color:(1,0,0,1)

Any widget called after its creation will be created with those attributes.