Python | Relative Layout in Kivy using .kv file

Kivy is a platform independent GUI tool in Python. As it can be run on Android, IOS, linux and Windows etc. It is basically used to develop the Android application, but it does not mean that it can not be used on Desktops applications.

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Relative Layout:

• This layout operates in the same way as FloatLayout does, but the positioning properties (x, y, center_x, right, y, center_y, and top) are relative to the Layout size and not the window size.
• In reality regardless of absolute and relative positioning, the widgets are moved when the position of the layout changes.
• The available pos_hint keys (x, center_x, right, y, center_y, and top) are useful for aligning to edges or centering. For example: pos_hint: {‘center_x’:.5, ‘center_y’:.5} would align a Widget in the middle, no matter what the size of the window is.

The first thing we need to do to use a RelativeLayout is import it.

from kivy.uix.relativelayout import RelativeLayout

We can do relative positioning by: pos_hint: provide hint of position. We can define upto 8 keys i.e. it takes arguments in form of dictionary. pos_hint = {“x”:1, “y”:1, “left”:1, “right”:1, “center_x”:1, “center_y”:1, “top”:1, “bottom”:1(“top”:0)}

Note: Floatlayout and RelativeLayout both support absolute and relative positioning depending upon whether pos_hint or pos is used.But If you want absolute positioning, use the FloatLayout.

Basic Approach to create Relative Layout:
1) import kivy
2) import kivy App
3) import Relativelayout
4) Set minimum version(optional)
5) create class for layout 
6) create App class:
        - define build() function
7) Set up.kv file(name same as the App class)
8) return Layout Class
9) Run an instance of the class

Below is the Implementation: main.py file

Python3

## Sample Python application demonstrating the
## working of RelativeLayout in Kivy using .kv file

###################################################
# import modules

import kivy

# base Class of your App inherits from the App class.
# app:always refers to the instance of your application
from kivy.app import App

# This layout allows you to set relative coordinates for children.
from kivy.uix.relativelayout import RelativeLayout

# To change the kivy default settings
# we use this module config
from kivy.config import Config

# 0 being off 1 being on as in true / false
# you can use 0 or 1 && True or False
Config.set('graphics', 'resizable', True)


# creating the root widget used in .kv file
class RelativeLayout(RelativeLayout):
    pass

# creating the App class in which name
#.kv file is to be named Relative_Layout.kv
class Relative_LayoutApp(App):
    # defining build()
    def build(self):
        # returning the instance of root class
        return RelativeLayout()

# run the app
if __name__ == "__main__":
    Relative_LayoutApp().run()

.kv file implementation :

Python3

#.kv file implementation of RelativeLayout

# creating button feature
<Button>:
        # size of text on button
        font_size: 20

        # creating button
        # a button 20 % of the width and 20 %
        # of the height of the layout
        size_hint: 0.2, 0.2

<RelativeLayout>:

        # The Canvas is the root object
        # used for drawing by a Widget.

        canvas:
                Color:
                        rgb:0, 1, 1
                Rectangle:
                        # creating rectangle
                        # pos = 20 % and size = 60 % of the layout
                        pos:[0.2 * coord for coord in self.size]
                        size:[0.6 * coord for coord in self.size]


        # creating the button

        Button:

                text:"B1"

                background_color: 0.1, 0.5, 0.6, 1

                # positioned at 0 % in x axis and 0 % in y axis
                # from bottom left, i.e x, y = 0, 0 from bottom left:
                pos_hint: {"x":0, "y":0}

        Button:
                text:"B2"
                background_color: 1, 0, 0, 1
                pos_hint: {"right":1, "y":0}


        Button:
                text:"Yash"
                background_color: 0.4, 0.5, 0.6, 1
                pos_hint: {"center_x":.5, "center_y":.5}

        Button:
                text:"B3"
                background_color: 0, 0, 1, 1
                pos_hint: {"x":0, "top":1}

        Button:
                text:"B4"
                background_color: 0.8, 0.9, 0.2, 1
                pos_hint: {"right":1, "top":1}

Output: Different size of window images are there which show that How it adjust itself accordingly to window i.e relatively Image 1: Image 2: Image 3: Reference: https://kivy.org/doc/stable/api-kivy.uix.relativelayout.html