归档
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归档，就是把需要保存的对象转换成NSData，然后存在本地，等下次需要使用的时候，再解归档，然后就可以使用了
第一种方法（只能存一个，最简单）
NSString *str =@"成本价";
//归档
NSData *data = [NSKeyedArchiverarchivedDataWithRootObject:str];
//存本地
[data writeToFile:@"/Users/qianfeng/Desktop/aaa"atomically:NO];
//从本地读取
data = [NSDatadataWithContentsOfFile:@"/Users/qianfeng/Desktop/aaa"];
//拿到对象
NSString *newStr = [NSKeyedUnarchiverunarchiveObjectWithData:data];
NSLog(@"%@",newStr);
第二种方法（可以存多个对象）
NSString *str1 =@"独孤求败";
NSString *str2 = @"东方不败";
userItem *user = [[userItem alloc] init];
user.name = @"西方不败";
// str1 + str2 = data
NSMutableData *data = [NSMutableDatadata];
//把归档的对象都放在data里
NSKeyedArchiver *archiver = [[NSKeyedArchiveralloc] initForWritingWithMutableData:data];
[archiver encodeObject:str1 forKey:@"str1"];
[archiver encodeObject:str2 forKey:@"str2"];
[archiver encodeObject:user forKey:@"user"];
[archiver finishEncoding];
//拿出对象
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiveralloc] initForReadingWithData:data];
NSString *newStr1 = [unarchiver decodeObjectForKey:@"str1"];
NSString *newStr2 = [unarchiver decodeObjectForKey:@"str2"];
userItem *newUser = [unarchiver decodeObjectForKey:@"user"];
[unarchiver finishDecoding];
NSLog(@"newStr1 is%@ , newStr2 is %@ , user is %@",newStr1,newStr2,newUser.name);
补充：
如果想要归档自定义的类对象的时候，就需要遵守NSCoding协议，写相关的协议方法
自定义类.h
//想让自定义的类支持归档，需要添加NSCoding协议
@interface userItem :NSObject<NSCoding>
@property(nonatomic,copy)NSString *name;
@end
//外界不能直接归档userItem,首先userItem先把自己的所有属性依次归档，然后外界再对userItem归档
@implementation userItem
-(id)initWithCoder:(NSCoder *)aDecoder
{
self.name = [aDecoder decodeObjectForKey:@"name"];
return self;
}
-(void)encodeWithCoder:(NSCoder *)aCoder
{
[aCoder encodeObject:self.nameforKey:@"name"];
}
@end
