Updating an NSMutableArray passed into a method

Question

I'm very new to objective-c so be easy :-) I have a container object, "Data", who has a number of NSMutableArrays.

Data.h

@interface Data : NSObject{

    NSMutableArray *one;
    NSMutableArray *two;    
}

@property (nonatomic, retain) NSMutableArray *one;

@end

and would like to pass it to a load method in which case it will update each corresponding array in the Data class.

Parser.h

+ (Parser *)load:(Data*) store;

Parser.m

+ (Parser *)load:(Data *) store {
...

[store.one addObject:name.stringValue];
}

But no matter what I do the string in "name.stringValue" doesn't get appended to the array. Is there something I'm missing when passing in the "Store" data object to the parse method? Let me know if I should provide more details but I feel this covers the issue.

Are you sure your array is properly initialized? Just having a property doesn't initialize it, it may just be nil and sending a message to nil doesn't throw an exception. — Zorayr
– Zorayr, Commented Jan 28, 2015 at 5:44
+ (NSMutableArray *)load:(Data *) store { NSMutableArray * store = [[NSMutableArray alloc]init]; for(NSString *str in store) { [store addObject:name.stringValue]; } return store; } try like this — Arun
– Arun, Commented Jan 28, 2015 at 5:53
Spynet - I get an error since that is redefining what "store" is. It's being passed in as a "Data" type whereas your setting it to NSMutableArray. — flying brick
– flying brick, Commented Jan 28, 2015 at 5:58
I tried initializing it in the parse method by doing: store.one = [[NSMutableArray alloc]init]; but no luck — flying brick
– flying brick, Commented Jan 28, 2015 at 6:02

Zorayr · Accepted Answer · 2015-01-28 05:58:43Z

1

Check in your implementation of Data that you are properly initializing the mutable arrays - here is a simple example below given your Data interface:

#import "Data.h"

@implementation Data
{

#pragma mark - Properties

- (NSMutableArray *)one
{
  if (!_one) {
    _one = [[NSMutableArray alloc] init];
  }
  return _one;
}

- (NSMutableArray *)two
{
  if (!_two) {
    _two = [[NSMutableArray alloc] init];
  }
  return _two;
}

}

answered Jan 28, 2015 at 5:58

Zorayr

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6 Comments

flying brick Over a year ago

Excuse the newbie comment but why is there a "one" and a "_one"? Is the underscored _one being magically generated somewhere?

Zorayr Over a year ago

Yeh, it's the default instance accessor... to access the variable directly, use _one, to access it through the getter within the class use, self.one, to access it outside of the class use, instanceObjectName.one.

flying brick Over a year ago

Thanks. I'm just getting back into compiled code after quite some time so the gears are slowly turning :-) This approach, while it works, seems really verbose for no more than initializing an array. Is there a more concise way to perform this action short of one main 'init' function?

flying brick Over a year ago

One more question while were on the subject of constructors/initialization. How would i go about creating an NSArray of class properies so i could loop through and allocate memory? Haven't gotten very far with using NSArray initWithObjects. Thanks!

Zorayr Over a year ago

To your earlier comment, you can also override your constructor and initialize your arrays... if you search for, "Objective-c override constructor" you will find more information.

|

krishnanunni · Accepted Answer · 2015-01-28 05:58:31Z

0

Use one = [NSMutableArray array]; before you start using it. This will create an empty mutable array.

answered Jan 28, 2015 at 5:58

krishnanunni

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