NSDictionary changes when a copy is changed

Question

I'm new to ObjectiveC and Xcode and make mistakes. This bit of code gets a dictionary (myDataPlist) from getAllRecords. I then make a mutable copy of a dictionary (1 record) within (myDataPlist) and decrypt 1 field with it. This works perfectly. I return just that record (mutCopy). This works also. My problem is the original dictionary (myDataPlist) changes. It The record that is decrypted is also decrypted in (myDataPlist). The 2 NSLog(@"%@",myDataPlist) return different results. I must be missing something. Why is (myDataPlist) changing?

Thanks for the help.

-(NSDictionary *)getRecordForKey:(NSString *)key{

    NSDictionary *myDataPlist = [self getAllRecords];
    NSMutableDictionary *mutCopy = [[myDataPlist valueForKey:key] mutableCopy];
    NSArray *keys = [mutCopy allKeys];
    NSData *tData = [[NSData alloc]init];
    NSLog(@"%@",myDataPlist);
    for (int x = 0; x <= [keys count] - 1; x++) {
        if (![keys[x] isEqualToString:@"Template"] && ![keys[x] isEqualToString:@"RecNum"]) {

        NSMutableArray *myArray = [mutCopy objectForKey:keys[x]];
        tData = myArray[1];
        NSString *tString = [tData decryptData:tData withKey:self.settingsManager.masterPad];
        myArray[1] = tString;
        [mutCopy setObject:myArray forKey:keys[x]];

        }
    }
    NSLog(@"%@",myDataPlist);
    return mutCopy ;
}

score 3 · Answer 1 · edited Apr 23 '13 at 02:32

3

mutableCopy creates a copy of the dictionary only and not the contents of it. So the dictionary that you receive from [[myDataPlist valueForKey:key] mutableCopy] is essentially a new dictionary with references to the same objects (it's not a deep copy).

Try using

NSMutableDictionary *mutCopy = 
    [[NSMutableDictionary alloc] initWithDictionary:[myDataPlist valueForKey:key] 
                                          copyItems:YES];

instead of mutableCopy.

From Apple documentation:

otherDictionary

A dictionary containing the keys and values with which to initialize the new dictionary.

flag

If YES, each object in otherDictionary receives a copyWithZone: message to create a copy of the object—objects must conform to the NSCopying protocol. In a managed memory environment, this is instead of the retain message the object would otherwise receive. The object copy is then added to the returned dictionary. If NO, then in a managed memory environment each object in otherDictionary simply receives a retain message when it is added to the returned dictionary.

If your dictionary contains custom objects, make sure that they conform to the NSCopying protocol.

edited Apr 23 '13 at 02:32

matt

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answered Apr 23 '13 at 02:10

Suhas

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I tried this and it causes an exception on the line myArray[1] = tString. Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray replaceObjectAtIndex:withObject:]: mutating method sent to immutable object – Camillo Scarcella Apr 23 '13 at 02:51
I must have seen that coming!!! :) This is happening because the array is no longer mutable. Replace NSMutableArray *myArray = [mutCopy objectForKey:keys[x]]; with NSMutableArray *myArray = [NSMutableArray arrayWithArray:[mutCopy objectForKey:keys[x]]];. That should get you going. – Suhas Apr 23 '13 at 03:16
You could also try the solution provided in this question http://stackoverflow.com/questions/5453481/how-to-do-true-deep-copy-for-nsarray-and-nsdictionary-with-have-nested-arrays-di – Suhas Apr 23 '13 at 03:27
Thank you, this absolutely fixed my problem and I actually understand most of it, though I don't know why myArray became immutable. I'll figure it out. Again, thank you very much – Camillo Scarcella Apr 23 '13 at 21:10

NSDictionary changes when a copy is changed

1 Answers1