Handling Touch Events In Kivy

Overview:

  • Kivy dispatches any touch event on the app to the root widget class.

 

  • A touch event could be any of the following
    • Down event
    • Up event
    • Move event

 

  • In Kivy, the root widget passes the event to all of its children while the children can pass the event to further down to their children.

 

  • This way, it is not only the widget within whose physical boundaries the touch event occurred receive the event. Other widgets also receive the touch event.

 

  • When a touch event occurs it is first received by one of the on_touch_xxx() handlers of the root widget.

 

  • Once received an event can be digested by the Kivy widget meaning it need not be propagated to the children or it can be propagated to the children.

 

 

Example:

from kivy.uix.button import Button

from kivy.app import App

 

# Customized button

class AppButton(Button):

    # Handle touch - an up event

    def on_touch_down(self, touch):

        if self.collide_point(*touch.pos):

            self.text = "Touch down"

            # digest the event

            return False

 

    # Handle touch - a down event

    def on_touch_up(self, touch):

        if self.collide_point(*touch.pos):

            self.text = "Touch me...."

            # touch is on the button...do not want to send this event any further

            return False

 

 

# App class

class TouchDemo(App):

 

    def build(self):

        appButton = AppButton(text = "Touch me...")

        return appButton

       

if __name__ == '__main__':

    TouchDemo().run()       

 

Output:

Handling touch (down) event kivy

Handling touch (up) event kivy


Copyright 2018 © pythontic.com