Due back button application get crashed in apk file

[Jayesh Kamble]

I written a simple code for log in application

in this i define a function for change the screen

for Example :-- First screen to Second screen and back to Second screen to First screen

This is work very well and good to fit

But when i use Mobile back button to for second screen to First screen, Its get crashed

I used a function also with 27 key input  and it is below

   

def key_input(self, window, key, scancode, codepoint, modifier):

if key == 27:

return True

else:

return False

Using this 27 key input application still get crashed

so how overcome on that and how to solve it this problem

here is my code below

https://pastebin.com/i4yG9Uzg