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 · Answer 1 · 2019-03-11T06:11:46.923

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

勿绮语 · Accepted Answer · 2012-02-15T03:01:06.900

22

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

edited Feb 15 '12 at 03:01

answered Nov 04 '11 at 23:34

勿绮语

9,170
1
29
37

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? – Ahoura Ghotbi Nov 04 '11 at 23:36
5

Create an instance of the class and call the instance method on that instance… – Arkku Nov 04 '11 at 23:37
6

You seem not to have grasped the core concepts of OOP. Have you assimilated docs like this one? http://www.otierney.net/objective-c.html – Cyrille Nov 04 '11 at 23:42
@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 – Ahoura Ghotbi Nov 09 '11 at 01:16

score 9 · Answer 3 · answered Nov 04 '11 at 23:35

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 04 '11 at 23:35

Cyrille

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ok so how can I create a class method to access it from other classes while I have access to the instance variables? – Ahoura Ghotbi Nov 04 '11 at 23:37
3

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`. – Cyrille Nov 04 '11 at 23:39

score 4 · Answer 4 · answered Nov 03 '14 at 00:04

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;
}

Instance variable 'variable' accessed in class method error

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