Styling with Kivy Language - UI Design with Kivy

Introduction

Kivy is a Python GUI library that allows developers to quickly create cross-platform applications with beautiful and interactive user interfaces. Kivy uses a custom language called Kivy Language (KV) to describe the user interface and the behaviors of all the widgets in the application. KV provides a simple, intuitive, and powerful way to design and style your application.

Syntax

The syntax of Kivy Language is based on indentation, similar to Python. Here is an example of KV code:

<MyLabel>:
    text: "Hello, Kivy!"
    color: 0, 1, 0, 1
    font_size: 40

In the above example, we are defining a custom label widget called MyLabel and setting its text, color and font size properties.

Example

Here is a simple example of using KV language to style an application:

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


class MyButton(Button):
    pass


class MyApp(App):
    def build(self):
        return MyButton(text='Click me')


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

We can create a kv file named my.kv and define the style for MyButton widget.

<MyButton>
    background_normal: 'button_normal.png'
    background_down: 'button_pressed.png'
    color: 0, 1, 0, 1

In the above example, we set the background images and text color for MyButton widget.

Output

When we run the above code, it will display a button with a green text on it, and clicking on it will change the background image to a pressed state image.

Explanation

In the above example, we first defined a custom widget called MyButton which inherits from the Button widget. Next, we created our App class called MyApp, and in its build() method, we returned an instance of MyButton widget.

In the KV code, we set the background_normal and background_down properties to the filenames of the images we want to use for the normal and pressed states of the button. We also set the text color to green.

Use

The KV language can be used to:

• Define the user interface of the application.
• Set the style of each of the widgets, such as background, text color, font, etc.
• Define the behavior of the widgets, such as on_press, on_release, on_touch_down, etc.

Important Points

• KV code can be used to apply a global style to the entire application or to specific widgets.
• KV supports inheritance, which allows us to create a base style and then inherit and modify it in another widget.
• KV files must have the same name as the class it is styling, with a .kv.

Summary

this tutorial, we learned about Kivy Language, syntax, example, output, explanation, use, important points, and summary of styling with Kivy Language. Kivy Language provides a simple and powerful way to create and style user interfaces in Python. With Kivy Language, you can easily apply custom styles to each of the widgets in your application.