objective-c properties - getters and setters

Question

In a UIView subclass I have this property:

@property (nonatomic) CGFloat scale;

#define DEFAULT_SCALE 0.90

and this getter and setter:

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

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

}

This isn't correct, because for example checking self.scale in the getter causes an infinite loop. What is the proper way to write the getter and setter so that I don't get infinite looping?

Answer 1

You should be able to access the ivar directly as _scale. Your getter/setter would then look like:

Update: As @wattson12 points out in the comments below you will need to add an @synthesize to your implementation.

@synthesize scale = _scale;

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

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

}

Answer 2

well I can think of about 3 ways to do this and be 0 aware.

@interface someClass
{
    BOOL useCustomScale;
}
@property float scale;
@end
@implimentation someClass
-(float)scale
{
    if(useCustomScale)
    {return scale;}
    return defaultScale;
}
-(void) setScale: (float)someScale
{
    useCustomScale = YES;
    scale = someScale
}

else you could use an NSNumber for backing the scale value...
else you could initialize the scale to -1 and make that an illegal value in the setter.
0 is typically a very bad thing to use for your test because you may very well want 0 to be valid value.