xcode 如何测试 BOOL 是否存在于 NSUserDefaults 用户设置中？
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How do I test if BOOL exists in NSUserDefaults user settings?
提问by Justin Copeland
I set a BOOL value in NSUserDefaults as follows.
我在 NSUserDefaults 中设置了一个 BOOL 值，如下所示。
[userDefaults setBool:NO forKey:@"theKeyOfMyBOOL"];
Somewhere else in my code, I want to perform some action if the key "theKeyOfMyBOOL" is not set in NSUserDefaults. How do I verify whether this key was set? If I do
如果在 NSUserDefaults 中未设置键“theKeyOfMyBOOL”，我想在代码的其他地方执行一些操作。如何验证是否设置了此密钥？如果我做
[userDefaults boolForKey:@"theKeyOfMyBOOL"];
then the value returned could be nil, which evaluates to false I believe, or the actual BOOL value of NO, which values to false.
那么返回的值可能是 nil，我相信它的计算结果为 false，或者 NO 的实际 BOOL 值，其值为 false。
However, I need to differentiate between these two values (as well as YES of course). How do I reliably do that?
但是，我需要区分这两个值（当然还有 YES）。我如何可靠地做到这一点？
回答by jrturton
[userDefaults boolForKey:@"theKeyOfMyBOOL"];returns a BOOL, so either YESor NO(not nil).
[userDefaults boolForKey:@"theKeyOfMyBOOL"];返回一个 BOOL，所以要么YESor NO(not nil)。
Internally, it is stored as an NSNumber. So, if you call
在内部，它存储为NSNumber. 所以，如果你打电话
[userDefaults objectForKey:@"theKeyOfMyBOOL"];
you will be given an NSNumber, if you have ever stored anything, or nil, if you have not.
NSNumber如果您曾经存储过任何东西，您将获得一个，或者nil，如果您没有存储过。
