NSUserDefaults读取和写入自定义对象
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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:
- 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
- @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:
- 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] ;
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- NSUserDefaults读取和写入自定义对象
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