Kivy is an open-source Python framework for developing multitouch applications. It provides a wide range of tools and functionalities for creating interactive and visually appealing user interfaces. One of the key features of Kivy is the ability to handle events and user interactions. While Kivy provides several built-in events, there may be cases where you want to create your own custom events.

In this blog post, we will explore how to create custom events in Kivy using Python. We will walk through an example to illustrate the process step by step.

Step 1: Importing the necessary modules

Firstly, we need to import the necessary modules from Kivy:

from kivy.app import App
from kivy.uix.button import Button
from kivy.event import EventDispatcher
from kivy.properties import BooleanProperty, ObjectProperty

Step 2: Creating a custom event class

Next, we will create a custom event class by inheriting from the EventDispatcher class:

class CustomEvent(EventDispatcher):
    my_event = BooleanProperty(False)
    my_data = ObjectProperty(None)

In this example, we have defined a custom event called my_event, which is of type BooleanProperty. We have also defined a property called my_data, which is of type ObjectProperty.

Step 3: Dispatching the custom event

Now, we can use the custom event in our application. Let’s create a simple Kivy app with a button that will dispatch our custom event:

class MyApp(App):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self.custom_event = CustomEvent()

    def on_custom_event(self):
        print("Custom event triggered!")

    def build(self):
        btn = Button(text='Click me!')
        btn.bind(on_release=lambda instance: setattr(self.custom_event, 'my_event', True))
        btn.bind(on_release=lambda instance: setattr(self.custom_event, 'my_data', 'Custom data'))
        btn.bind(on_release=lambda instance: self.custom_event.dispatch('on_custom_event'))
        return btn

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

In this code, we create an instance of our custom event class CustomEvent in the MyApp class. We then define an on_custom_event method that will be called when the custom event is triggered. Inside the build method, we create a button and bind the on_release event to set the my_event property of our custom event to True, set the my_data property to “Custom data”, and dispatch the custom event.

Step 4: Handling the custom event

To handle the custom event, we need to bind a callback function to it. In our example, we have defined the on_custom_event method in the MyApp class as the callback function. This method will be called when the custom event is dispatched:

def on_custom_event(self):
    print("Custom event triggered!")

In this example, we simply print a message when the custom event is triggered. However, you can perform any desired actions in the callback function based on your application’s requirements.

Conclusion

Creating custom events in Kivy allows you to extend the functionality of your application and handle user interactions in a more flexible way. By following the steps outlined in this blog post, you can easily create and dispatch custom events in Kivy using Python. Experiment with different event types and properties to add interactivity to your Kivy applications.