Overview

The NSUserDefaults class provides a programmatic interface for interacting with the defaults system. The defaults system allows an application to customize its behavior to match a user’s preferences. For example, you can allow users to determine what units of measurement your application displays or how often documents are automatically saved. Applications record such preferences by assigning values to a set of parameters in a user’s defaults database. The parameters are referred to as defaults since they’re commonly used to determine an application’s default state at startup or the way it acts by default.

At runtime, you use anNSUserDefaults object to read the defaults that your application uses from a user’s defaults database.NSUserDefaults caches the information to avoid having to open the user’s defaults database each time you need a default value. Thesynchronize method, which is automatically invoked at periodic intervals, keeps the in-memory cache in sync with a user’s defaults database.

The NSUserDefaults class provides convenience methods for accessing common types such as floats, doubles, integers, Booleans, and URLs. A default object must be a property list, that is, an instance of (or for collections a combination of instances of):NSData,NSString, NSNumber, NSDate, NSArray, orNSDictionary. If you want to store any other type of object, you should typically archive it to create an instance ofNSData. For more details, seePreferences and Settings Programming Guide.

Values returned fromNSUserDefaults are immutable, even if you set a mutable object as the value. For example, if you set a mutable string as the value for"MyStringDefault", the string you later retrieve using stringForKey: will be immutable.

A defaults database is created automatically for each user. TheNSUserDefaults class does not currently support per-host preferences. To do this, you must use the CFPreferences API (seePreferences Utilities Reference). However, NSUserDefaults correctly reads per-host preferences, so you can safely mix CFPreferences code withNSUserDefaults code.

If your application supports managed environments, you can use anNSUserDefaults object to determine which preferences are managed by an administrator for the benefit of the user. Managed environments correspond to computer labs or classrooms where an administrator or teacher may want to configure the systems in a particular way. In these situations, the teacher can establish a set of default preferences and force those preferences on users. If a preference is managed in this manner, applications should prevent users from editing that preference by disabling any appropriate controls.

The NSUserDefaults class is thread-safe.

Tasks

Getting the Shared NSUserDefaults Instance

• + standardUserDefaults
• + resetStandardUserDefaults

Initializing an NSUserDefaults Object

• – init
• – initWithUser:Deprecated in OS X v10.9

Registering Defaults

• – registerDefaults:

Getting Default Values

• – arrayForKey:
• – boolForKey:
• – dataForKey:
• – dictionaryForKey:
• – floatForKey:
• – integerForKey:
• – objectForKey:
• – stringArrayForKey:
• – stringForKey:
• – doubleForKey:
• – URLForKey:

Setting Default Values

• – setBool:forKey:
• – setFloat:forKey:
• – setInteger:forKey:
• – setObject:forKey:
• – setDouble:forKey:
• – setURL:forKey:

Removing Defaults

• – removeObjectForKey:

Maintaining Persistent Domains

• – synchronize
• – persistentDomainForName:
• – removePersistentDomainForName:
• – setPersistentDomain:forName:
• – persistentDomainNamesDeprecated in OS X v10.9

Accessing Managed Environment Keys

• – objectIsForcedForKey:
• – objectIsForcedForKey:inDomain:

Managing the Search List

• – dictionaryRepresentation

Maintaining Volatile Domains

• – removeVolatileDomainForName:
• – setVolatileDomain:forName:
• – volatileDomainForName:
• – volatileDomainNames

Maintaining Suites

• – addSuiteNamed:
• – removeSuiteNamed:

翻译上面NSUserDefaults的API大概意思例如以下:

NSUserDefaults类提供了一个与默认系统进行交互的编程接口。NSUserDefaults对象是用来保存，恢复应用程序相关的偏好设置。配置数据等等。

默认系统同意应用程序自己定义它的行为去迎合用户的喜好。你能够在程序执行的时候从用户默认的数据库中读取程序的设置。同一时候NSUserDefaults的缓存避免了在每次读取数据时候都打开用户默认数据库的操作。能够通过调用synchronize方法来使内存中的缓存与用户默认系统进行同步。

NSUserDefaults类提供了很方便的方法来获取经常使用的类型，比如floats,doubles,intergers,Booleans,URLs。所以一个NSUserDefaults的对象必须是属性表，这也就是说我们能够存储NSData,NSString,NSNUmber,NSDate,NSArray,NSDictionary这些实例。

假设你想存储其它类型的对象，你要将其归档并创建一个NSData来实现存储。

从NSUserDefaults返回的值是不可改变的。即便是你在存储的时候使用的是可变的值。比如你使用mutable string做为“MyStringDefault”的值。当你做使用stringForKey:方法获取的值。这个值仍然是不可变的。

NSUserDefaults是单例，同一时候也是线程安全的.

方法具体解释

获取公有的NSUserDefaults实例

 + (NSUserDefaults *)standardUserDefaults;
 单例模式，获取NSUserDefaults的一个实例。默认Key值例如以下：
 AppleLanguages,
 AppleKeyboardsExpanded,
 AppleITunesStoreItemKinds,
 AppleLocale,
 AppleKeyboards,
 NSLanguages,
 NSInterfaceStyle

 + (void)resetStandardUserDefaults;

初始化一个NSUserDefaults的对象

 - (id)init;
 - (id)initWithUser:(NSString *)username;
 init是初始化一个公有的defaults对象
 initWithUser是初始化一个针对username的对象

注冊一个defaults

 - (void)registerDefaults:(NSDictionary *)registrationDictionary;
 注冊的内容(registrationDictionary里的)不写入磁盘

获取Defaults的值

 - (NSArray *)arrayForKey:(NSString *)defaultName;

 - (BOOL)boolForKey:(NSString *)defaultName;
 返回一个和defaultName关联的bool值，假设不存在defaultName的话返回NO

 - (NSData *)dataForKey:(NSString *)defaultName
 返回defaultName所相应的NSData数据，假设defaultName不存在或者返回的数据不是NSData类型的都会返回nil
 返回的数据是不可变类型的

 - (NSDictionary *)dictionaryForKey:(NSString *)defaultName
 同dataForKey

 - (float)floatForKey:(NSString *)defaultName
 同dataForKey
 假设defaultName不存在返回0

 - (NSInteger)integerForKey:(NSString *)defaultName
 同floatForKey
 假设defaultName不存在返回0

 - (id)objectForKey:(NSString *)defaultName
 同dataForKey

 - (NSArray *)stringArrayForKey:(NSString *)defaultName
 同dataForKey
 假设defaultName不存在，或者defaultName所相应的不是一个数组，或者数组包括的不是NSString对象都会返回nil

 - (NSString *)stringForKey:(NSString *)defaultName
 同dataForKey

 - (double)doubleForKey:(NSString *)defaultName
 同floatForKey

 - (NSURL *)URLForKey:(NSString *)defaultName
 同dataForKey
 当调用[NSUserDefaults URLForKey:]时。有下面3种情况：
 1.假设值是NSData,NSData能够作为[NSKeyedUnarchiver unarchiveObjectWithData:]的參数。假设NSData能够作为NSURL存档就返回一个NSURL。否则返回nil
 2.假设值是一个文件引用的URL，那么这个文件引用的URL将会被创建，可是它的书签数据不会被解决直到以后使用NSURL实例
 3.假设值是一个一～开头的字符串，这个字符串将会用[NSString stringByExpandingTildeInPath]扩展，文件将会以NSURL创建

设置Defaults值

 – setBool:forKey:
 – setFloat:forKey:
 – setInteger:forKey:
 – setDouble:forKey:

 – setObject:forKey:
 对象參数仅仅能是属性列表对象：NSData，NSString，NSNumber,NSDate,NSArray,NSDictionary
 – setURL:forKey:

移除Defaults值

 - (void)removeObjectForKey:(NSString *)defaultName

维护持久域

 - (BOOL)synchronize
 把持久域中的不论什么改变写到磁盘而且更新磁盘上的不论什么没有改动的持久域
 假设返回YES表明成功保存到磁盘，相反返回NO
 这种方法是以一定周期间隔自己主动调用的，假设你不想等待自己主动调用就能够调用这种方法来同步。(比如。假设你的应用要退出时，或者你想更新磁盘上的defaults即使你没有做不论什么改变)

 - (NSDictionary *)persistentDomainForName:(NSString *)domainName
 返回一个特定持久域的键值对

 - (NSArray *)persistentDomainNames
 返回当前的持久域的名称

 - (void)removePersistentDomainForName:(NSString *)domainName
 移除相应domainName的持久域

 - (void)setPersistentDomain:(NSDictionary *)domain forName:(NSString *)domainName
 设置持久域
 domainName
 This value should be equal to your application's bundle identifier.

訪问管理的环境值

 - (BOOL)objectIsForcedForKey:(NSString *)key
 - (BOOL)objectIsForcedForKey:(NSString *)key inDomain:(NSString *)domain

管理搜索列表

 - (NSDictionary *)dictionaryRepresentation
 返回搜索列表中相应域的全部的键值对

维护不稳定的域

 – removeVolatileDomainForName:
 – setVolatileDomain:forName:
 – volatileDomainForName:
 – volatileDomainNames

维护套件

 - (void)addSuiteNamed:(NSString *)suiteName
 一个套件能够在不同的应用之间使用

 - (void)removeSuiteNamed:(NSString *)suiteName
 移除套件

演示样例代码例如以下:

#pragma mark---------存    //创建 NSUserDefaults 单例    NSUserDefaults * ud = [NSUserDefaults standardUserDefaults];    //把_userNameTextField.text存到  NSUserDefaults 中    [ud setObject:_userNameTextField.text forKey:@"myKey"];    [ud synchronize];#pragma mark---------取    //从 NSUserDefaults 中取出 数据    NSString * value = [ud objectForKey:@"myKey"];    NSLog(@"value = %@",value);

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