Instance variable 'variable' accessed in class method error

Question

I have a variable declared in the header file :

@interface

int _nPerfectSlides;

and

@property (nonatomic, readwrite) int _nPerfectSlides;

and I have a method that I declared in the header :

+ (void) hit;

The method has the following code in it :

+ (void) hit {
    NSLog(@"hit");
    _nPerfectSlides = 0;
    [_game showHit];
}

now for some reason I get the error "Instance variable '_nPerfectSlides' accessed in class method" error and it seems like I cant access any variables inside the method. What am I doing wrong?

Rajesh Loganathan · Accepted Answer · 2019-03-11 06:11:46Z

25

1. For + (void)hit:Only have access to the self object.

--Step 1: Remove follwing line from header file

@property (nonatomic, readwrite) int _nPerfectSlides;

--Step 2:

Add int _nPerfectSlides in your class file globally..
That means declare before @implementation

Eg: In .m File

#import "Controller.h"
int _nPerfectSlides // Add like this before @implementation

@implementation Controller

2. For - (void)hit:Only have access to the instance methods

edited Mar 11, 2019 at 6:11

answered May 5, 2014 at 11:16

Rajesh Loganathan

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Comments

勿绮语 · Accepted Answer · 2012-02-15 03:01:06Z

22

If you meant to make this an instance method, change that + to -.

edited Feb 15, 2012 at 3:01

answered Nov 4, 2011 at 23:34

勿绮语

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4 Comments

Ahoura Ghotbi Over a year ago

Yea I tried that before posting, it fixed this issue but when I try calling the method from another class it crashes... what shall I do?

Arkku Over a year ago

Create an instance of the class and call the instance method on that instance…

Cyrille Over a year ago

You seem not to have grasped the core concepts of OOP. Have you assimilated docs like this one? otierney.net/objective-c.html

Ahoura Ghotbi Over a year ago

@Cyrille you are right, I am new to OOP tbh, used to structured coding. I am reading a few docs around the net and trying to figure it out and also shape up my OOP. but thanks anyways

Cyrille · Accepted Answer · 2011-11-04 23:35:54Z

9

An instance variable is, as its name suggests, only accessible in the instance methods (those declared with -). Class methods (declared with +) have no access to instance variable, no more than they have access to the self object.

answered Nov 4, 2011 at 23:35

Cyrille

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2 Comments

Ahoura Ghotbi Over a year ago

ok so how can I create a class method to access it from other classes while I have access to the instance variables?

Cyrille Over a year ago

I don't understand your comment. Either you change your + (void) hit into a - (void) hit, or you declare _nPerfectSlides on a global level, outside of your class' @interface.

SmileBot · Accepted Answer · 2014-11-03 00:04:11Z

4

I know this is old, but it still comes up. Try making it a static. Here's I'm altering the code a bit to make it increment.

// Hit.h

#import <Foundation/Foundation.h>
@interface Hit : NSObject
+ (void)hit;
@end

// Hit.m

#import "Hit.h"
@implementation Hit
static int val = 0;
+ (void)hit {
    val += 1;
    [self showHit];
}
+ (void)showHit {
    NSLog(@"hit value: %d", val);
}
@end

//main.m

#import <Foundation/Foundation.h>
#import "Hit.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        [Hit hit];
        [Hit hit];
        [Hit hit];
    }
    return 0;
}

answered Nov 3, 2014 at 0:04

SmileBot

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