前言
NSUserDefaults支持的數(shù)據(jù)類型有：NSNumber（NSInteger建椰、float、double）吮蛹，NSString，NSDate拌屏，NSArray潮针，NSDictionary，BOOL.
附：NSUserDefaults 雖然本身不支持自定義對象的存儲倚喂，不過它支持NSData的類型每篷。所以當我們要在NSUserDefaults中存儲的是自定義的對象的時候，需要將該自定義對象轉(zhuǎn)成NSData存儲端圈。而自定義對象轉(zhuǎn)data的方式我們通過<NSCoding>來實現(xiàn)焦读。這里提前講到，下面會詳細介紹舱权。
1矗晃、NSUserDefaults 存儲數(shù)組問題
①如果數(shù)組中的對象不是自定義的對象，那么可直接存儲宴倍。如：
NSArray *array = @[@"1", @"2", @"3", @"4"];
[[NSUserDefaults standardUserDefaults] setObject:array forKey:@"key"];
[[NSUserDefaults standardUserDefaults] synchronize];
②如果數(shù)組中的對象是自定義的對象张症，那么需要先讓這個自定義類實現(xiàn)<NSCoding>協(xié)議中的- (id) initWithCoder: (NSCoder *)coder方法和- (void) encodeWithCoder: (NSCoder *)coder方法，然后把該自定義的類對象編碼到NSData中鸵贬，再從NSUserDefaults中進行讀取俗他。
//User.h
@interface User : NSObject<NSCoding> //注意：這里需要實現(xiàn)NSCoding協(xié)議
@property (nonatomic, copy) NSString *realName;
@property (nonatomic, copy) NSString *nickName;
@property (nonatomic, copy) NSString *password;
@end
//User.m
@implementation User
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
if (self = [super init]) {
self.realName = [aDecoder decodeObjectForKey:@"realName"];
self.nickName = [aDecoder decodeObjectForKey:@"nickName"];
self.password = [aDecoder decodeObjectForKey:@"password"];
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:self.realName forKey:@"realName"];
[aCoder encodeObject:self.nickName forKey:@"nickName"];
[aCoder encodeObject:self.password forKey:@"password"];
}
@end
這時，存儲自定義對象的數(shù)組的獲取與保存方法如下
//存儲
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSArray *array = @[customObject1, customObject2, customObject3, customObject4];
NSData *arrayData = [NSKeyedArchiver archivedDataWithRootObject:array];
[userDefaults setObject:arrayData forKey:@"arrayKey"];
[userDefaults synchronize];
//取出
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSData *arrayData = [userDefaults objectForKey:@"arrayKey"];
NSArray *array = [NSKeyedUnarchiver unarchiveObjectWithData:arrayData];
2阔逼、NSUserDefaults 存儲自定義對象的問題見上
3兆衅、修改存儲在NSUserDefaults中的數(shù)組
廢話不多說上代碼,項目中遇到的問題是:
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSMutableArray *array = [userDefaults objectForKey:@"theArrayKey"]];
[array addObject:@"some new value"];
[userDefaults setObject: array forKey:@"theArrayKey"]; //會卡住主程序
[[NSUserDefaults standardUserDefaults] synchronize];
這句話取出了數(shù)組,可是當對數(shù)組添加元素后,進行存儲時卡在了下面這句話:
[userDefaults setObject: array forKey:@"theArrayKey"];
時候會把主線程卡住,但是不崩潰,不知道為何,就Google了,stackoverflow給了解答辦法,
When you store mutable objects to NSUserDefaults, it stores an immutable copy of it so you can't change it directly like that. You have to get the mutable copy out of defaults, change it, and then set it back, replacing old object in defaults.
即：修改存儲在NSUserDefaults中的數(shù)組：我們從NSUserDefaults中取出的數(shù)組是不可變的(因為NSUserDefaults 存儲的對象全是不可變的)。所以當我們需要修改存儲在NSUserDefaults中的數(shù)組時嗜浮，需要用一個新的可變數(shù)組來保存之前的值羡亩，再修改，之后再保存危融，即修改的過程應(yīng)該如下：
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
NSMutableArray *array = [userDefaults objectForKey:@"theArrayKey"]];
NSMutableArray *mutableCopyArray = [array mutableCopy]; //重要步驟操作mutableCopyArray
[mutableCopyArray addObject:@"some new value"];
[userDefaults setObject: mutableCopyArray forKey:@"theArrayKey"];
[[NSUserDefaults standardUserDefaults] synchronize];
總結(jié)：NSUserDefaults 存儲的對象全是不可變的（這一點非常關(guān)鍵畏铆，弄錯的話程序會出bug），即存進NSUserDefaults的對象會變成不可變的专挪，同樣取出來的對象肯定是不可變的及志。
