Question

I have a simple Answer class that looks like this:

@interface Answer : NSObject {
  NSString *_text;
  NSNumber *_votes;
}

@property(nonatomic, retain) NSString *text;
@property(nonatomic, retain) NSNumber *votes;

+(id)initFromAnswerData:(NSSet *)data;
-(id)initWithText:(NSString *)answer;

@end

The implementation looks like this:

#import "Answer.h"
#import "AnswerData.h"
#import "AppDelegate.h"

@implementation Answer

@synthesize text = _text;
@synthesize votes = _votes;


-(id)initWithText:(NSString *)answer {
  if( (self=[super init])) {
    _text = answer;
    _votes = 0;
  }
  return self;
}


@end

If I create an array of Answers in a view controller using the initWithText: method I inevitably have EXC_BAD_ACCESS errors when I take an Answer in the array and try to find it’s text value.

However if I initialize a new Answer, set the text value and then add it to the array I don’t have this access issue.

So this causes problems down the line:

[arrayOfAnswers addObject:[[Answer alloc] initWithText:@"Hello"]];

But this doesn’t:

Answer *newAnswer = [[Answer alloc] initWithText:nil];
newAnswer.text = @"Hello";
[arrayOfAnswers addObject:newAnswer];

Can anyone explain why?

Answer 1

You’re using the attribute _text and _votes directly but not their setters.
So, you’re not retaining the input parameter answer for the line

_text = answer;

You should either change to

_text = [answer retain];

or

self.text = answer;