January 2020
Intermediate to advanced
356 pages
6h 4m
Chinese
Content preview from Swift游戏开发经典实例
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164
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第
5
章
有时，在
UserDefaults
中提供一些默认值是很有必要的，特别是当用户没有为某
个值提供一个确切的值时，默认值将变得很有用。
例如，假设游戏开始的第一关是“关卡
1
”，我们将玩家所通过的关卡以
currentLevel
的名字存放到
UserDefaults
中。当游戏启动时，我们会从
UserDefaults
中查询
currentLevel
值，然后初始化游戏：
let levelNumber = defaults.integer (forKey: "currentLevel")
但是，如果玩家是第一次玩这个游戏，那会发生什么样的情况？如果
currentLevel
没有指定任何值，当这句代码第一次执行时，我们会得到一个
0
，这是完全不对的，
因为我们的游戏是从关卡“
1
”开始。
要解决这个问题，我们可以注册默认值。也就是给
UserDefaults
提供一个由键
–
值对构成的字典，这样当某些值未被指定的情况下就使用字典中指定的默认值：
let defaultValues = ["currentLevel": 1]
defaults.register(defaults: defaultValues)
let levelNumber = defaults.integer(forKey: "currentLevel")
// levelNumber
的值要么是
1
，要么是最后一次保存在
UserDefaults
中的相应值
如果用户想修改我们存放在
UserDefaults
中的值，这真的是非常非常的简
单。某些第三方工具能够直接访问和修改存放在 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.