Why you should use Kivy in your next python app

Python’s Kivy framework is a powerful tool for creating cross-platform mobile and desktop applications. It’s user-friendly and easy to…

Kivy is an open-source Python framework for creating cross-platform user interfaces. This means that developers can use Kivy to create applications that work on multiple platforms, such as Android, iOS, Windows, and macOS.

One of the key features of Kivy is the use of a kv file. This file, also known as a kivy language file, is a text file that contains instructions for building the user interface of a Kivy application. The kv file uses a simple, declarative syntax that allows developers to quickly and easily create complex layouts and widgets.

The main advantage of using a kv file is that it allows developers to separate the layout and design of their application from the underlying code. This means that developers can focus on writing the logic of their application, while designers can work on creating an attractive and intuitive user interface.

Layouts

There are several different types of layouts that are possible with Kivy. Some of the most common layouts include BoxLayout, GridLayout, and StackLayout. Each of these layouts allows developers to arrange the widgets within their application in a specific way.

BoxLayout

For example, a BoxLayout allows developers to arrange widgets in a horizontal or vertical box. This is useful for creating simple, straightforward layouts that allow users to easily navigate through the application.

Source: Kivy Docs

The .kv code:

BoxLayout:
    orientation: 'vertical'
    Label:
        text: 'this on top'
    Label:
        text: 'this right aligned'
        size_hint_x: None
        size: self.texture_size
        pos_hint: {'right': 1}
    Label:
        text: 'this on bottom'

GridLayout

A GridLayout, on the other hand, allows developers to arrange widgets in a grid, with each widget occupying a specific row and column. This is useful for creating complex, grid-based layouts that can display a large amount of data in an organized and intuitive way.

Source: Kivy Docs

StackLayout

Finally, a StackLayout allows developers to arrange widgets in a stack, with each widget appearing on top of the previous one. This is useful for creating layered, hierarchical layouts that can be used to create menus, navigation bars, and other interactive elements.

Source: Kivy Docs

A simple widget

In addition to the different types of layouts, Kivy also provides a wide range of simple widgets that can be used to build user interfaces. Some of the most common widgets include buttons, labels, text inputs, and images.

To demonstrate how simple widgets work in Kivy, let’s take a look at a simple example that shows how to create a button and change its text when it is clicked.

First, we need to import the Button and App classes from the Kivy library:

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

Next, we need to create a subclass of the App class that will contain the logic for our application. This class will define the build() method, which will be called when the application is started.

class MyApp(App):
    def build(self):
        pass

Inside the build() method, we can create a Button widget and set its text to “Click me!”:

class MyApp(App):
    def build(self):
        button = Button(text="Click me!")
        return button

Finally, we can add an on_press event handler to the Button widget that will be called when the button is clicked. Inside this event handler, we can change the text of the button to “Hello, world!”:

class MyApp(App):
    def build(self):
        button = Button(text="Click me!")
        button.bind(on_press=self.on_button_pressed)
        return button

    def on_button_pressed(self, instance):
        instance.text = "Hello, world!"

Now, when the user clicks the button, the on_button_pressed() method will be called and the text of the button will be changed to “Hello, world!”.

In conclusion, the Kivy framework for Python provides an easy-to-use and powerful tool for creating cross-platform user interfaces. The use of a kv file allows developers to quickly and easily create complex layouts and widgets, and the different types of layouts and simple widgets provide a wide range of possibilities for building user interfaces. By following the examples in this blog post, you can start using Kivy to create your own user interfaces and build engaging and interactive applications.