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:
view plaincopy to clipboardprint?
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
view plaincopy to clipboardprint?
@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:
view plaincopy to clipboardprint?
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] ;
以上的代码时由另一个程序中截取的,没有测试过,但意思就是这样了。
如果一个自定义类中由另一个自定义类对象,那么所有嵌套的类都要实现<NSCoding>。