如何解决外星人入侵-Pygame-外星人离开屏幕
我正在从《 Python Crash Course》一书中制作“外星人入侵”游戏项目，并卡住了外星人舰队应该向右走直到到达屏幕右边缘，改变方向并向左走等等的地方
问题是我的外星人确实改变了方向，但是只有当街区中的第一个外星人（第一个一直在左边）碰到屏幕的右边缘时。他右边的所有外星人都经过右边缘。
似乎无法识别应该先打右边缘的右边外星人的直肠，而只能识别一直到左边的第一个外星人的直肠...
我正在严格按照书中的说明进行操作，现在我检查了3次可能存在问题的地方。您能帮我找到问题吗？
alien_invasion.py
import sys
import pygame
from settings import Settings
from ship import Ship
from bullet import Bullet
from alien import Alien
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.ship = Ship(self)
self.bullets = pygame.sprite.Group()
self.aliens = pygame.sprite.Group()
self._create_fleet()
# Set the background color.
self.bg_color = (230,230,230)
def run_game(self):
"""Start the main loop for the game."""
while True:
self._check_events()
self.ship.update()
self._update_bullets()
self._update_aliens()
self._update_screen()
def _check_events(self):
"""Respond to keypresses 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)
def _check_keydown_events(self,event):
"""Respond to keypresses."""
if event.key == pygame.K_RIGHT:
# Move the ship to the right.
self.ship.moving_right = True
elif event.key == pygame.K_LEFT:
# Move the ship to the left.
self.ship.moving_left = True
elif event.key == pygame.K_q:
# Exit the game after pressing Q:
sys.exit()
elif event.key == pygame.K_SPACE:
self._fire_bullet()
def _check_keyup_events(self,event):
"""Respond to keypresses."""
if event.key == pygame.K_RIGHT:
# Stop moving the ship to the right.
self.ship.moving_right = False
elif event.key == pygame.K_LEFT:
# Stop moving the ship to the left.
self.ship.moving_left = False
def _fire_bullet(self):
"""Create a new bullet and add it to the bullets 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 bullets and get rid of old bullets."""
# Update bullets positions.
self.bullets.update()
# Get rid of bullets that have dissapeared.
for bullet in self.bullets.copy():
if bullet.rect.bottom <= 0:
self.bullets.remove(bullet)
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()
"""Update the positios of all aliens in the fleet."""
self.aliens.update()
def _create_fleet(self):
"""Create a 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 // (4 * 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 + 4 * alien_width * alien_number
alien.rect.x = alien.x
alien.rect.y = alien.rect.height + 3 * 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 _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)
pygame.display.flip()
if __name__ == '__main__':
# Make a game instance,and run the game.
ai = AlienInvasion()
ai.run_game()
settings.py
class Settings:
"""A class to store all settings for Alien Invasion."""
def __init__(self):
"""Initialize the game's settings."""
# Screen settings
self.screen_width = 1200
self.screen_height = 800
self.bg_color = (230,230)
self.ship_speed = 1.5
# Bullet settings
self.bullet_speed = 1.0
self.bullet_width = 3
self.bullet_height = 15
self.bullet_color = (60,60,60)
self.bullets_allowed = 3
# Alien settings
self.alien_speed = 1.0
self.fleet_drop_speed = 10
# fleet_direction of 1 represents right; -1 represents left.
self.fleet_direction = 1
alien.py
import pygame
from pygame.sprite import Sprite
class Alien(Sprite):
"""A class to represent a single alien in the fleet."""
def __init__(self,ai_game):
"""Initialize the alien and set its starting postion."""
super().__init__()
self.screen = ai_game.screen
self.settings = ai_game.settings
# Load the alien image and set its rect attribute.
self.image = pygame.image.load('images/alien.bmp')
self.rect = self.image.get_rect()
# Start each new alien near the top left of the screen.
self.rect.x = self.rect.width
self.rect.y = self.rect.height
# Store the alien's exact horizontal position.
self.x = float(self.rect.x)
def check_edges(self):
"""Return True if an alien is at edge of screen."""
screen_rect = self.screen.get_rect()
if self.rect.right >= screen_rect.right or self.rect.left <= 0:
return True
def update(self):
"""Move the alien right or left."""
self.x += self.settings.alien_speed * self.settings.fleet_direction
self.rect.x = self.x
解决方法
这是Indentation的问题。您需要找到第一个撞到边缘的外星人，然后打破循环。实际上，您总是会在列表中的第一个敌人之后中断循环：
class AlienInvasion:
# [...]
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()
#-->| INDENTATION
break
# break <-- DELETE
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