Question

Possible Duplicate:
property not working with getter AND setter

this is the problem I’m facing: I’m using iOS 6. I declare a property in the header file:

@property (nonatomic) CGFloat scale;

Then in the implementation, I create my own getter/setter like this:

#define DEFAULT_SCALE 0.90    

- (void)setScale:(CGFloat)scale
{
    if(_scale != scale) {
        _scale = scale;
        [self setNeedsDisplay];
    }
}

- (CGFloat) scale
{
    if(!_scale) {
        return DEFAULT_SCALE;
    } else {
        return _scale;
    }
}

the problem is that _scale is not recognized by compiler. I get error “Use of undeclared identifier ‘_scale’.
If I remove the getter or the setter, then it works fine, but I can’t keep both. If I do, I have to add @synthesize scale = _scale to avoid the error. Can someone explain why?

Thanks

Answer 1

You need to declare the instance variable in the @interface if you’re going to use your own setter/getter:

@interface MyClass : NSObject
{
    CGFloat _scale;
}
...
@end

EDIT (after OP question):

Your particular implementation certainly makes a difference (they aren’t simple getter/setter methods as they do something as a side-effect). However I think it’s always a good idea to declare your variables and absolutely necessary if you want to target 32-bit OSX, as the runtime doesn’t support auto-declared instance variables.