NSUserDefaults boolforKey 设计上的限制吗？
NSUserDefaults API 文档具有 boolForKey: 消息，其描述如下 -
boolForKey:
返回与指定键关联的布尔值。
- (BOOL)boolForKey:(NSString *)defaultName
返回值 如果布尔值与用户默认值中的 defaultName 关联，则返回该值。否则，返回NO。
如果 [[NSUserDefaults standardUserDefaults] boolForKey:@"some_Key"] 返回一个 NO，则可能是因为该键不存在，或者该键存在并且具有一个 boolean 数值编号我们如何区分？事到如今，我只能从一开始就避免陷入这种境地。
The NSUserDefaults API documentation has the boolForKey: message which is described like this -
boolForKey:
Returns the Boolean value associated with the specified key.
- (BOOL)boolForKey:(NSString *)defaultName
Return Value
If a boolean value is associated with defaultName in the user defaults, that value is returned. Otherwise, NO is returned.
Given that a [[NSUserDefaults standardUserDefaults] boolForKey:@"some_Key"] gives back a NO it can be either because the key does not exist or the key exists and has a boolean value NO. How can we differentiate? As of now, I can only avoid getting into this situation in the first place.
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您错误地使用了用户默认值。在启动应用程序时，您应该使用包含所有首选项的默认值的字典来调用
-[NSUserDefaults registerDefaults:]。然后，如果用户未设置首选项，
-boolForKey将返回默认值。You are using the user defaults incorrectly. At the launch of your app, you are supposed to call
-[NSUserDefaults registerDefaults:]with a dictionary that contains the default values for all preferences.Then, if the user has not set a preference,
-boolForKeywill return the default value.也可以使用
-objectForKey:方法。这将告诉您该密钥是否存在。Use the
-objectForKey:method as well. This will tell you whether the key exists.