NSCoding and ARC

Question

I'd like to archive my custom objects. ClassA holds a dictionary whose values are instances of ClassB.

Everything looks good ClassA's initWithCoder, and _dictionary is declared strong, but after init returns and I call callMeAfterInit, the _dictionary is empty (not null, a valid empty dictionary).

This ought to be simple, but I haven't used archiving much, so maybe I'm missing something basic. What might cause the dictionary to be emptied after the init returns?

Here's the essential code:

@interface ClassA : NSObject <NSCoding>
@property (strong, nonatomic) NSMutableDictionary *dictionary;
@end

@implementation ClassA

- (void)encodeWithCoder:(NSCoder *)encoder {

    [encoder encodeObject:self.dictionary forKey:@"dictionary"];
}

- (id)initWithCoder:(NSCoder *)decoder {

    self = [super init];
    if (self) {
        _dictionary = [decoder decodeObjectForKey:@"dictionary"];
        // breakpoint here and I can inspect a good dictionary, full of ClassB values
    }
    return self;
}

- (void)callMeAfterInit {

    NSLog(@"%@", self.dictionary);
    // Log output here shows an empty dictionary (valid, but with 0 pairs)
}

@end


@interface ClassB : NSObject <NSCoding>
@property (strong, nonatomic) NSNumber *number;
@property (strong, nonatomic) NSArray *array;
@end

@implementation ClassB

- (void)encodeWithCoder:(NSCoder *)encoder {

    [encoder encodeObject:self.number forKey:@"number"];
    [encoder encodeObject:self.array forKey:@"array"];
}

- (id)initWithCoder:(NSCoder *)decoder {

    self = [super init];
    if (self) {
        _number = [decoder decodeObjectForKey:@"number"];
        _array = [decoder decodeObjectForKey:@"array"];
    }
    return self;
}

@end

Answer 1

You don't show the code that calls callMeAfterInit, so this is a guess.

More likely than not, you aren't talking to the same instance of ClassA. Did you happen to call [[ClassA alloc] init]; somewhere?