Question

I am stumped, im not very good with Objective-C yet, and I have been following tutorials until now.

I have decided to add all the functions I use in multipul views in one “CommonClass” I have called GeneralHelper.

When trying to call my function im getting the following error:

Instance method’-convertPoint:’ not found(return type defaults to
‘id’)

Below is my code:

My GeneralHelper.h lookslike this:
#import

    @interface GeneralHelper : NSObject

    @end

    GeneralHelper* gHelper;

My GeneralHelper.m looks like this:

    #import "GeneralHelper.h"
    #import "WhackGame.h"
    #import "SimpleAudioEngine.h"
    #import "Settings.h"

    @implementation GeneralHelper
    -(CGPoint)convertPoint:(CGPoint)point {
        if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
            return ccp(32 + point.x*2, 64 + point.y*2);
        } else {
            return point;
        }
    }

    @end

Inside my Initialize method I have:

    gHelper = [[GeneralHelper alloc] init]; //First, we create an instance of GeneralHelper

and im trying to call it like:

    mole1.position = [gHelper convertPoint:ccp(85, 85)];

Any ideas?

Thanks

Answer 1

You didn’t declare the method convertPoint: in your @interface like this:

@interface GeneralHelper : NSObject
- (CGPoint)convertPoint:(CGPoint)point;
@end

Also, if you’re trying to have one shared instance of GeneralHelper, that’s not the way to do it. Instead you should have a class method that returns an instance.

@interface GeneralHelper : NSObject
- (CGPoint)convertPoint:(CGPoint)point;
+ (GeneralHelper *)sharedHelper;
@end

Then in your implementation:

+ (GeneralHelper *)sharedHelper
{
    static GeneralHelper *sharedHelper = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedHelper = [[GeneralHelper alloc] init];
    });
    return sharedHelper;
}

And then wherever you need it:

CGPoint convertedPoint = [[GeneralHelper sharedHelper] convertPoint:point];

Alternatively you could simply use class methods:

@interface GeneralHelper : NSObject
+ (CGPoint)convertPoint:(CGPoint)point;
@end

The implementation is the same as before, but with a + instead of a – sign. In this case you don’t need the sharedHelper method and can simply call it like this:

CGPoint convertedPoint = [GeneralHelper convertPoint:point];