How to save a (custom) NSObject in Core Data

Question

In my application i have an custom NSObject, which contains 2 mutable Arrays. I need to save this custom NSOBject into a core data entity, but i have no real idea how i can accomplish that...

After some searching, i found out, that the best way would be to convert the nsobject to nsdata and save it in an transformable field of the entity... but i m not sure how to do that. can someone help me?

heres to code for my custom object:

MeasureData.h

@interface MeasureData : NSObject{
}

@property (nonatomic, strong) NSMutableArray *questionsData;
@property (nonatomic, strong) NSMutableArray *answersData;

- (id) init;

@end

MeasureData.m

#import "MeasureData.h"

@implementation MeasureData

@synthesize questionsData;
@synthesize answersData;

#pragma mark -
#pragma mark int

- (id)init
{
self = [super init];

// Initalize questions array (width data from plist)
questionsData = self.makeQuestionsArray;
// NSLog(@"loaded questions array: %@",questionsData); // debug


// Initalize answers array
answersData = self.makeAnswersArray;
// NSLog(@"loaded answers array: %@",answersData); // debug


return self;
}

-(NSMutableArray *)makeQuestionsArray
{
// Initalize questions array (width data from plist)
NSString *path = [[NSBundle mainBundle] pathForResource:
                  @"questions.list" ofType:@"plist"];
NSMutableArray *questions = [NSMutableArray arrayWithContentsOfFile:path];


/*
 [questionsData insertObject:(NSString *)string atIndex:0];
 */

return questions;
}

-(NSMutableArray *)makeAnswersArray
{
// Initalize answers array
NSMutableArray *answers = [NSMutableArray arrayWithCapacity:0];

return answers;
}

-(id)initWithCoder:(NSCoder *)decoder {
if ((self=[super init])) {
    questionsData = [decoder decodeObjectForKey:@"questionsData"];
    answersData = [decoder decodeObjectForKey:@"answersData"];
}
return self;
}

-(void)encodeWithCoder:(NSCoder *)encoder {
[encoder encodeObject:questionsData forKey:@"questionsData"];
[encoder encodeObject:questionsData forKey:@"questionsData"];
}

@end

According to the first comment, i implemented the encoder/coder functions for my custom class. And tried to archive and encode it (i m new to ios, so it could be completly wrong) - but it dont work... can someone tell me whats wrong?

heres the encoding (which dont work XD):

NSMutableData *dataToSave = (NSMutableData *)self.measureData;
NSKeyedArchiver *archiverForData = [[NSKeyedArchiver alloc] initForWritingWithMutableData:dataToSave];

[archiverForData encodeObject:dataToSave forKey:@"dataToSave"];
[archiverForData finishEncoding];
//

//theMeasure is the CoreData Entity
theMeasure.result = dataToSave;

what is self.measureData type? You should create a new, empty NSMutableData object instead of casting your measureData ivar (I guess it will be MeasureData type) and use encodeObject:self.measeureData on your original object. Also note, you copy-pasted 2 times the same line in encodeWithCoder. — MrTJ, Mar 19 '12 at 14:28
thank you ;) i know use a slightly different approach (maybe its the same, i m not sure) => i take my object and use "NSData *dataToSave = [NSKeyedArchiver archivedDataWithRootObject:measureData];" to convert it to NSData -> this NSData can be stored in a binary attribute and can be reconvertet via NSKeyUnarchiver... pretty easy, but took me about 4 houres trying and trying. — jacksbox, Mar 19 '12 at 16:43
yes, this way I meant originally! Don't sorry for that 4h, I am sure you studied a lot ;) PS: if you think so, you can also "accept" my answer by clicking on the white ticker under the +/- counter. — MrTJ, Mar 19 '12 at 16:46
^^ oh yes - i learned a lot ;) thank you for your answere - it lead me the way XD — jacksbox, Mar 19 '12 at 16:56

score 2 · Accepted Answer · edited May 23 '17 at 11:58

2

In outline:

create a NSMutableData
create a NSKeyedArchiver with initForWritingWithMutableData over your data
serialize your arrays / objects / whatever you need (that implements NSCoding) with encode... methods of NSCoder
create a managed object with a BLOB (binary data) type field
write your encoded data from the mutable data to this field of the managed object.

In my answer to this question you can find some useful links: NSCoding VS Core data

edited May 23 '17 at 11:58

Community

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answered Mar 19 '12 at 12:59

MrTJ

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hm, tank you, that sounds good - i also tried your suggestion, but i cant make it work - i added my tries to my question, so maybe u could have a look and give me a hint what to do or what i m doing wrong? – jacksbox Mar 19 '12 at 14:10

How to save a (custom) NSObject in Core Data

1 Answers1