ios NSUserDefaults 是否包含值？
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NSUserDefaults Contains Value Or Not?
提问by Aswathy Bose
How to know whether NSUserDefaultscontains any value?How to check whether its empty?
如何知道是否NSUserDefaults包含任何值？如何检查是否为空？
回答by Krishnabhadra
There isn't a way to check whether an object within NSUserDefaults is empty or not. However, you can check whether a value for particular key is nil or not.
没有办法检查 NSUserDefaults 中的对象是否为空。但是，您可以检查特定键的值是否为零。
NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
NSObject * object = [prefs objectForKey:@"your_particular_key"];
if(object != nil){
//object is there
}
回答by Parag Bafna
NSUserDefaults *data = [NSUserDefaults standardUserDefaults];
NSString *string = [data objectForKey:@"yourKey"];
if(string==nil)
NSlog(@"nil")
Take a look at NSUserDefault documentation
// For saving the values
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
// saving an NSString
[userDefaults setObject:@"Ttest" forKey:@"key"];
// --- For Retrieving
NSUserDefaults * userDefaults = [NSUserDefaults standardUserDefaults];
// getting an NSString
NSString *myString = [userDefaults stringForKey:@"key"];
回答by hamstergene
To check whether a specific value is set or not, no matter of its location (global or application's), check the returned value of -[NSUserDefaults objectForKey:]
要检查是否设置了特定值，无论其位置（全局或应用程序的）如何，请检查返回的值 -[NSUserDefaults objectForKey:]
id obj = [[NSUserDefaults standardUserDefaults] objectForKey:@"My-Key-Name"];
if (obj != nil) {...}
To check if the application (bundle) has any settings stored in user defaults:
要检查应用程序（捆绑包）是否在用户默认值中存储了任何设置：
NSUserDefaults* sdu = [NSUserDefaults standardUserDefaults];
NSString* bundleId = [[NSBundle mainBundle] bundleIdentifier];
NSDictionary* mainBundleSettings = [sdu persistentDomainForName:bundleId];
NSLog(@"%@", mainBundleSettings);
If you are interested in all possible values for which -[NSUserDefaults objectForKey:]will return something, including system global settings, simply call
如果您对所有可能-[NSUserDefaults objectForKey:]返回的值感兴趣，包括系统全局设置，只需调用
NSDictionary* allPossibleSettings = [sdu dictionaryRepresentation];
NSUserDefaultsis never empty. It combines global settings, bundle's settings, temporary data and maybe something else. For example, if you call:
NSUserDefaults永远是空的。它结合了全局设置、bundle 的设置、临时数据以及其他一些东西。例如，如果您调用：
[[NSUserDefaults standardUserDefaults] objectForKey:@"NSBoldSystemFont"]
you will get the @"LucidaGrande-Bold"string value which will be taken from global settings, even when your application has never set this value.
您将获得@"LucidaGrande-Bold"将从全局设置中获取的字符串值，即使您的应用程序从未设置过该值。
