如何制作“外星人入侵”中的难度按钮？

Question

我最近在python速成班上从事外星人入侵项目。我遇到了一个任务，我必须为用户制作难度按钮。我想这样做，当用户运行游戏时，首先播放按钮将可用，在他单击播放按钮后，难度按钮（简单、中等、困难）将显示给用户

import sys
from time import sleep

import pygame

from settings import Settings
from game_stats import GameStats
from ship import Ship

from bullet import Bullet
from alien import Alien
from button import Button

class AlienInvasion:
    """Overall class to manage game assets and behavior."""

    def __init__(self):
        """Initialize the game, and create game resources."""
        pygame.init()
        self.settings = Settings()

        self.screen = pygame.display.set_mode((0, 0), pygame.FULLSCREEN)
        self.settings.screen_width = self.screen.get_rect().width
        self.settings.screen_height = self.screen.get_rect().height
        pygame.display.set_caption("Alien Invasion")

        self.stats = GameStats(self)
        self.ship = Ship(self)
        self.bullets = pygame.sprite.Group()
        self.aliens = pygame.sprite.Group()

        self._create_fleet()
        self.play_button = Button(self, "Play")
        self._make_difficulty_buttons()

    def run_game(self):
        """Start the main loop for the game."""
        while True:
            self._check_events()

            if self.stats.game_active:
                self.ship.update()
                self._update_bullets()
                self._update_aliens()

            self._update_screen()

    def _check_events(self):
        """Respond to key presses and mouse events."""
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
            elif event.type == pygame.KEYDOWN:
                self._check_keydown_events(event)
            elif event.type == pygame.KEYUP:
                self._check_keyup_events(event)
            elif event.type == pygame.MOUSEBUTTONDOWN:
                mouse_pos = pygame.mouse.get_pos()
                self._check_play_button(mouse_pos)

    def _check_play_button(self, mouse_pos):
        """Start a new game when the player clicks play."""
        button_clicked = self.play_button.rect.collidepoint(mouse_pos)
        if button_clicked:
            self._draw_difficulty_buttons()

    def _draw_difficulty_buttons(self):
        self.easy_button.draw_button()
        self.medium_button.draw_button()
        self.difficult_button.draw_button()

    def _make_difficulty_buttons(self):
        """Make buttons that allow the players to select difficulty levels"""
        self.easy_button = Button(self, "Easy")
        self.medium_button = Button(self, "Medium")
        self.difficult_button = Button(self, "Difficult")

        # Position buttons so they don't all overlap.
        self.easy_button.rect.top = (
            self.play_button.rect.top + 1.5*self.play_button.rect.height)
        self.easy_button._update_msg_position()

        self.medium_button.rect.top = (
            self.easy_button.rect.top + 1.5*self.easy_button.rect.height)
        self.medium_button._update_msg_position()

        self.difficult_button.rect.top = (
            self.medium_button.rect.top + 1.5*self.medium_button.rect.height)
        self.difficult_button._update_msg_position()


    def _check_keydown_events(self, event):
        """Respond to key presses"""
        if event.key == pygame.K_RIGHT:
            self.ship.moving_right = True
        elif event.key == pygame.K_LEFT:
            self.ship.moving_left = True
        elif event.key == pygame.K_q:
            sys.exit()
        elif event.key == pygame.K_SPACE:
            self._fire_bullet()

    def _check_keyup_events(self, event):
        """Respond to key releases."""
        if event.key == pygame.K_RIGHT:
            self.ship.moving_right = False
        if event.key == pygame.K_LEFT:
            self.ship.moving_left = False

    def _fire_bullet(self):
        """Create a new bullet and add it to the group."""
        if len(self.bullets) < self.settings.bullets_allowed:
            new_bullet = Bullet(self)
            self.bullets.add(new_bullet)

    def _update_bullets(self):
        """Update position of the bullets and get rid of the old bullets."""
        self.bullets.update()
        # Get rid of bullets that have disappeared.
        for bullet in self.bullets.copy():
            if bullet.rect.bottom <= 0:
                self.bullets.remove(bullet)

        self._check_bullet_collisions()

    def _check_bullet_collisions(self):
        """Respond to bullet-alien collision"""
        # Check for any bullets that has hit aliens.
        # if so, get rid of the bullet and the alien
        collisions = pygame.sprite.groupcollide(
            self.bullets, self.aliens, True, True)

        if not self.aliens:
            # Destroy existing bullets and create a new fleet.
            self.bullets.empty()
            self._create_fleet()
            self.settings.increase_speed()

    def _update_aliens(self):
        """
        Check if the fleet is at an edge,
          then update the positions of all aliens in the fleet.
        """
        self._check_fleet_edges()
        self.aliens.update()

        # Look for alien-ship collision.
        if pygame.sprite.spritecollideany(self.ship, self.aliens):
            self._ship_hit()

        # Look for aliens hitting the bottom of the screen.
        self._check_aliens_bottom()

    def _create_fleet(self):
        """Create the fleet of aliens."""
        # Create an alien and find the number of aliens in a row.
        # Spacing between each alien is equal to one alien width.
        alien = Alien(self)
        alien_width, alien_height = alien.rect.size
        available_space_x = self.settings.screen_width - (2 * alien_width)
        number_aliens_x = available_space_x // (2 * alien_width)

        # Determine the number of rows of aliens that fit on the screen.
        ship_height = self.ship.rect.height
        available_space_y = (self.settings.screen_height -
                             (3 * alien_height) - ship_height)
        number_rows = available_space_y // (2 * alien_height)

        # Create the full fleet of aliens.
        for row_number in range(number_rows):
            for alien_number in range(number_aliens_x):
                self._create_alien(alien_number, row_number)

    def _create_alien(self, alien_number, row_number):
        """"Create an alien and place it in the row"""
        alien = Alien(self)
        alien_width, alien_height = alien.rect.size
        alien.x = alien_width + 2 * alien_width * alien_number
        alien.rect.x = alien.x
        alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
        self.aliens.add(alien)

    def _check_fleet_edges(self):
        """Respond appropriately if any aliens have reached an edge."""
        for alien in self.aliens.sprites():
            if alien.check_edges():
                self._change_fleet_direction()
                break

    def _change_fleet_direction(self):
        """Drop the entire fleet and change the fleet's direction."""
        for alien in self.aliens.sprites():
            alien.rect.y += self.settings.fleet_drop_speed
        self.settings.fleet_direction *= -1

    def _ship_hit(self):
        """Respond to the ship being hit by an alien."""
        if self.stats.ships_left > 0:
            # Decrement ships left
            self.stats.ships_left -= 1

            # Get rid of any remaining aliens and bullets
            self.aliens.empty()
            self.bullets.empty()

            # Create a new fleet and centre the ship
            self._create_fleet()
            self.ship.centre_ship()

            # Pause.
            sleep(1)
        else:
            self.stats.game_active = False
            pygame.mouse.set_visible(True)

    def _check_aliens_bottom(self):
        """Check if any aliens have reached the bottom of the screen."""
        screen_rect = self.screen.get_rect()
        for alien in self.aliens.sprites():
            if alien.rect.bottom >= screen_rect.bottom:
                # Treat this the same as if the ship got hit.
                self._ship_hit()
                break

    def _update_screen(self):
        """Update images on the screen, and flip to the new screen."""
        self.screen.fill(self.settings.bg_color)
        self.ship.blitme()
        for bullet in self.bullets.sprites():
            bullet.draw_bullet()
        self.aliens.draw(self.screen)

        # Draw the play button if the game is inactive.
        if not self.stats.game_active:
            self.play_button.draw_button()

        # Make the most recently drawn screen visible.
        pygame.display.flip()


if __name__ == '__main__':
    # Make a game instance, and run the game.
    ai = AlienInvasion()
    ai.run_game()

查找函数make_defestion_按钮、draw_defestion_按钮和check_play_按钮。在pygame检测到用户单击了播放按钮后的check_play_button方法中，我想使用draw_Demobility_buttons方法绘制难度按钮。但是在我的代码中，在我点击播放按钮后，什么都没有发生。请帮帮我。先谢谢你