Trouble Updating a Rectangle Using a Custom Property in Pygame

Question

I am debugging one of my programs where I am trying to assign a custom variable to a rectangle to update it's position.

Here is my code:

import os ; os.environ['PYGAME_HIDE_SUPPORT_PROMPT']='False'
import pygame, random

pygame.init()
display = pygame.display.set_mode((401, 401))
display.fill("white") ; pygame.display.flip()

class MyRect(pygame.Rect):

    def __setattr__(self, attr, value): # Sets a custom attribute to a rectangle
        super().__setattr__(attr, value)
        if attr == 'xValue':
            pygame.Rect.move(self, (value-self.centerx), 0) # Move the rectangle according to the xValue
    
    def contains(self, coords):
        return self.collidepoint(coords)

square = MyRect(175, 175, 50, 50)
pygame.draw.rect(display, 'steelBlue', square) # Draw the rectangle to the screen
square.xValue = 200

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit() ; exit()
        elif event.type == pygame.MOUSEBUTTONDOWN:
            if square.contains(pygame.mouse.get_pos()):
                square.xValue = random.randint(0, display.get_width()) # Update the square.xValue property
        pygame.display.flip() # Update the screen

When I execute the program, the square.xValue property is changing, but the position of the square on the screen is not.

What did I miss?

Answer 1

You have to redraw the scene. You have to redraw the rectangle after it has been changed. Clear the display and draw the rectangle in the application loop:

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit() ; exit()
        elif event.type == pygame.MOUSEBUTTONDOWN:
            if square.contains(pygame.mouse.get_pos()):
                square.xValue = random.randint(0, display.get_width()) # Update the square.xValue property

    display.fill("white");   
    pygame.draw.rect(display, 'steelBlue', square)     
    pygame.display.flip() # Update the screen