//NSDictionary  ==>NSData类型：NSDictionary *targetDictionary;NSMutableData *data = [[NSMutableData alloc] init]; NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];[archiver encodeObject : targetDictionary forKey : @"Custom Key”];[archiver finishEncoding];

//NSData类型转换为NSDictionary类型:NSData *data;NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];NSDictionary *myDictionary = [[unarchiver decodeObjectForKey:@"Custom Key"] retain];[unarchiver finishDecoding];

//NSDictionary转换JSON：NSString *jsonStr=[dict JSONRepresentation];