存储数据 NSUSERDEFAULTS 读取和写入

<NSCODING> 存储数据 NSUSERDEFAULTS 读取和写入

NSUserDefaults读取和写入自定义对象 
NSUserDefaults可以存取一些短小的信息。

比如存入再读出一个字符串到NSUserDefaults：



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NSString *string= [NSString stringWithString @"hahaha"];  
NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];  
[ud setObject:string forKey:@"myKey"];  
NSString *value;  
value = [ud objectForKey:"myKey"];  



但是并不是所有的东西都能往里放的。NSUserDefaults只支持： NSString, NSNumber, NSDate, NSArray, NSDictionary.

如果把一个自定义的类存到一个NSArray里，然后再存到NSUserDefaults里也是不能成功的。不信可以试试，如果你成功的请告诉我。

那怎么办呢？

我找到的方法是，让这个自定义类实现<NSCoding>协议中的- (id) initWithCoder: (NSCoder *)coder方法和- (void) encodeWithCoder: (NSCoder *)coder方法（obj-c的协议protocol就是java的接口interface，就是C++的纯虚函数），然后把该自定义的类对象编码到NSData中，再从NSUserDefaults中进行读取。

粘代码：

假设有这样一个简单的类对象



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@interface BusinessCard : NSObject <NSCoding>{  
    NSString *_firstName;  
    NSString *_lastName;  
}  
@property (nonatomic, retain) NSString *_firstName;  
@property (nonatomic, retain) NSString *_lastName;  
@end;  

@implementation BusinessCard  
@synthesize _firstName, _lastName;  
- (void)dealloc{  
    [_firstName release];  
    [_lastName release];  
    [super dealloc];  
}  
- (id) initWithCoder: (NSCoder *)coder  
{  
if (self = [super init])  
    {  
        self._firstName = [coder decodeObjectForKey:@"_firstName"];  
        self._lastName = [coder decodeObjectForKey:@"_lastName"];  
    }  
return self;  
}  
- (void) encodeWithCoder: (NSCoder *)coder  
{  
    [coder encodeObject:_firstName forKey:@"_firstName"];  
    [coder encodeObject:_lastName forKey:@"_lastName"];  

}  

@end



然后再存取时通过NSData做载体：



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BusinessCard *bc = [[BusinessCard alloc] init];  
NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];  
NSData *udObject = [NSKeyedArchiver archivedDataWithRootObject:bc];  
[ud setObject:udObject forKey:@"myBusinessCard"];  
[bc release];  
udObject = nil;  
udObject = [ud objectForKey:@"myBusinessCard"];  
bc = [NSKeyedUnarchiver unarchiveObjectWithData:udObject] ;