Merge pull request '206530220' (#7) from 206530220 into master

Reviewed-on: http://git.zjvtit.net/python-learning-2065300/206530219/pulls/7

ship.py

@@ -0,0 +1,50 @@
+import pygame
+from pygame.sprite import Sprite
+
+
+class Ship(Sprite):
+    def __init__(self, ai_settings, screen):
+        """初始化飞船并设置其初始位置"""
+        super(Ship, self).__init__()
+        self.screen = screen
+        self.ai_settings = ai_settings
+
+        self.image = pygame.image.load('images/ship.png')
+        self.rect = self.image.get_rect()
+        self.screen_rect = screen.get_rect()
+
+        # 将每艘新飞船放在屏幕底部中央
+        self.rect.centerx = self.screen_rect.centerx
+        self.rect.bottom = self.screen_rect.bottom
+
+        # 在飞船的属性center中存储小数值
+        self.centerx = float(self.rect.centerx)
+        self.centery = float(self.rect.centery)
+
+        # 移动标志
+        self.moving_right = False
+        self.moving_left = False
+        self.moving_up = False
+        self.moving_down = False
+
+    def update(self):
+        """根据移动标志调整飞船的位置"""
+        # 更新飞船的center值，而不是rect
+        if self.moving_right and self.rect.right < self.screen_rect.right:
+            self.centerx += self.ai_settings.ship_speed_factor
+        if self.moving_left and self.rect.left > 0:
+            self.centerx -= self.ai_settings.ship_speed_factor
+        if self.moving_up and self.rect.top > 0:
+            self.centery -= self.ai_settings.ship_speed_factor
+        if self.moving_down and self.rect.bottom < self.screen_rect.bottom:
+            self.centery += self.ai_settings.ship_speed_factor
+        # 根据self.center更新rect对象
+        self.rect.centerx = self.centerx
+        self.rect.centery = self.centery
+
+    def blitme(self):
+        self.screen.blit(self.image, self.rect)
+
+    def center_ship(self):
+        """让飞船在屏幕上居中"""
+        self.center = self.screen_rect.centerx