Python | Relative Layout in Kivy

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 Desktop applications.

Kivy Tutorial – Learn Kivy with Examples. 

Relative Layout:

• Relative layout is just similar to the FloatLayout the difference is that its child widget are positioned relative to the 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.
• When the widget with position=(0, 0) is added to RelativeLayout, Now if the position of RelativeLayout is changed the child widget will also move. The Child widget coordinates remains same i.e (0, 0) as they are always relative to the parent layout.
• 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 to import it. 

from kivy.uix.relativelayout import RelativeLayout

Note:
This layout allows you to set relative coordinates for children. If you want absolute positioning, use the FloatLayout. In RelativeLayout each child widget size and position has to be given. This also does the dynamic placement.

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 kivyApp
3) import button
4) import Relativelayout
5) Set minimum version(optional)
6) create App class:
        - define build() function
7) return Layout/widget/Class(according to requirement)
8) Run an instance of the class

Implementation of approach using pos : 
It simply assigns the position to the button. As Relativelayout does not depends on the window size it gets fixed to that position now if you do the window size small it may disappear rather than adjusting itself. 

Python3

# Sample Python application demonstrating the
# working of RelativeLayout in Kivy

# 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

# creates the button in kivy
# if not imported shows the error
from kivy.uix.button import Button

# 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 App class
class MyApp(App):

    def build(self):

        # creating Relativelayout
        Rl = RelativeLayout()

        # creating button
        # a button 30 % of the width and 20 %
        # of the height of the layout and
        # positioned at (x, y), you can do
        # The position does not depend on window size
        # it just positioned at the given places:
        btn = Button(text ='Hello world',
                 size_hint =(.2, .2),
                 pos =(396.0, 298.0))
        btn1 = Button(text ='Hello world !!!!!!!!!',
                 size_hint =(.2, .2),
                 pos =(-137.33, 298.0))

        # adding widget i.e button
        Rl.add_widget(btn)
        Rl.add_widget(btn1)

        # return the layout
        return Rl

# run the App
if __name__ == "__main__":
    MyApp().run()

Output:

Now if you want that the button adjusts itself according to window pos_hint is used. 

Implementation Approach by using pos_hint 

Python3

# Sample Python application demonstrating the
# working of RelativeLayout in Kivy

# 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

# creates the button in kivy
# if not imported shows the error
from kivy.uix.button import Button

# 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 App class
class Relative_Layout(App):

    def build(self):

        # creating Relativelayout
        rl = RelativeLayout()

        # creating button
        # size of button is 20 % by height and width of layout
        # position is bottom left i.e x = 0, y = 0
        b1 = Button(size_hint =(.2, .2),
                    pos_hint ={'x':0, 'y':0},
                    text ="B1")

        # position is bottom right i.e right = 1, y = 0
        b2 = Button(size_hint =(.2, .2),
                    pos_hint ={'right':1, 'y':0},
                    text ="B2")

        b3 = Button(size_hint =(.2, .2),
                    pos_hint ={'center_x':.5, 'center_y':.5},
                    text ="B3")

        b4 = Button(size_hint =(.2, .2),
                    pos_hint ={'x':0, 'top':1},
                    text ="B4")

        b5 = Button(size_hint =(.2, .2),
                    pos_hint ={'right':1, 'top':1},
                    text ="B5")



        # adding button to widget
        rl.add_widget(b1)
        rl.add_widget(b2)
        rl.add_widget(b3)
        rl.add_widget(b4)
        rl.add_widget(b5)


        # returning widget
        return rl
# run the App
if __name__  == "__main__":
    Relative_Layout().run()

Output: