NSKeyedArchiver archiveRootObject for an object inside an object doesn't work!

I have a Level class, witch contains another Class LevelPoints for some attributes, how can I archive the instance of Level by using

[projectDictionary setObject:level forKey:@"testlevel"];
[NSKeyedArchiver archiveRootObject:projectDictionary toFile:@"somewhere"];

I can not get the _levelPoints variable with values out of th开发者_如何转开发e [NSKeyedUnarchiver unarchiveObjectWithFile:DATAPATH];

Any ideas?

#import <Foundation/Foundation.h>

@interface Level : NSObject <NSCoding> {
    int _levelNum;
    float _spawnRate;
    NSString *_bgImageName;
    LevelPoints *_levelPoints;
}

@property (nonatomic, assign) int levelNum;
@property (nonatomic, assign) float spawnRate;
@property (nonatomic, copy) NSString *bgImageName;
@property (nonatomic, retain) LevelPoints *levelPoints;

- (id)initWithLevelNum:(int)levelNum spawnRate:(float)spawnRate bgImageName:(NSString *)bgImageName;

- (id)initWithCoder:(NSCoder *)aDecoder;
- (void)encodeWithCoder:(NSCoder *)aCoder;

@end


#import <Foundation/Foundation.h>


@interface LevelPoints : NSObject <NSCoding> {
    int _score;
    int _outflows;
    int _mistakes;
}
@property (nonatomic, assign) int score;
@property (nonatomic, assign) int outflows;
@property (nonatomic, assign) int mistakes;

- (id)initWithCoder:(NSCoder *)aDecoder;
- (void)encodeWithCoder:(NSCoder *)aCoder;
@end

Do you mean something like:

- (id)initWithCoder:(NSCoder *)aDecoder
{
  ...
  self.levelPoints = [aDecoder decodeObjectForKey: @"myKey"];
  ...
}

- (void)encodeWithCoder:(NSCoder *)aCoder
{
  ...
  [aCoder encodeObject:self.levelPoints forKey: @"myKey"];
  ...
}

EDIT: these implementations should go into the Level class.