How to serialize object containing NSData?

Question

I'm trying to serialize an object containing a number of data fields...where one of the fields is of datatype NSData which won't serialize. I've followed instructions at http://www.isolated.se but my code (see below) results in the error "[NSConcreteData data]: unrecognized selector sent to instance...". How do I serialize my object?

Header file:

@interface Donkey : NSObject<NSCoding>
{
   NSString* s;
   NSData* d;
}

@property (nonatomic, retain) NSString* s;
@property (nonatomic, retain) NSData* d;

- (NSData*) serialize;

@end

Implementation file:

@implementation Donkey

@synthesize s, d;

static NSString* const KEY_S = @"string";
static NSString* const KEY_D = @"data";

- (void) encodeWithCoder:(NSCoder*)coder
{
    [coder encodeObject:self.s forKey:KEY_S];
    [coder encodeObject:self.d forKey:KEY_D];
}

- (id) initWithCoder:(NSCoder*)coder;
{
    if(self = [super init])
    {
        self.s = [coder decodeObjectForKey:KEY_S];
        self.d = [coder decodeObjectForKey:KEY_D];
    }

    return self;
}

- (NSData*) serialize
{
    return [NSKeyedArchiver archivedDataWithRootObject:self];
}

@end

Answer 1

Your problem is most likely a naming collision caused by using data as a property name because otherwise the code looks fine and both NSString and NSData should serialize easily.

Try refactoring data into something like "theData" or "myData" and see if the issue resolves.