Question

I’m trying to subclass UIColor, and I can’t seem to figure out what’s wrong.

In my PColor.h

#import <Foundation/Foundation.h>
@interface PColor : UIColor {
    BOOL isAvailable;
    int colorId;
}
@property (nonatomic, assign) BOOL isAvailable;
@property (nonatomic, assign) int colorId;
@end

…and in my PColor.m

#import "PColor.h"

@implementation PColor
@synthesize isAvailable;
@synthesize colorId;
@end

Upon instantiating a PColor object, I get:

//warning: incompatible Objective-C types initializing 'struct UIColor *', expected 'struct PColor *'
PColor *pcolor = [[PColor alloc] initWithHue:1 saturation:0 brightness:0 alpha:1];

Am I missing something? Thanks in advance.

Answer 1

UIColor is a class cluster use associative references in a category to add properties! All of the custom init methods on UIColor return a UIColor* not an id so you can not easily subclass UIColor nor should you try.

UIColor+PCOLOR.h

#import <UIKit/UIKit.h>
#import <objc/runtime.h>

@interface UIColor(PCOLOR)
//Properties prefixed to try and avoid future conflicts
@property (nonatomic, assign) BOOL pIsAvailable;
@property (nonatomic, assign) int pColorId;
@end

UIColor+PCOLOR.h

#import "UIColor+PCOLOR.h"

@implementation UIColor(PCOLOR)

static char PCOLOR_ISAVAILABLE_KEY;
static char PCOLOR_COLORID_KEY;

@dynamic pIsAvailable, pColorId;

-(void)setPIsAvailable:(BOOL)pIsAvailable
{
    objc_setAssociatedObject(self, &PCOLOR_ISAVAILABLE_KEY, [NSNumber numberWithBool:pIsAvailable], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(BOOL)pIsAvailable
{
    return [(NSNumber*)objc_getAssociatedObject(self, &PCOLOR_ISAVAILABLE_KEY) boolValue];
}

-(void)setPColorId:(int)pColorId
{
    objc_setAssociatedObject(self, &PCOLOR_COLORID_KEY, [NSNumber numberWithInt:pColorId], OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

-(int)pColorId
{
    return  [(NSNumber*)objc_getAssociatedObject(self, &PCOLOR_COLORID_KEY) intValue];
}

@end

USAGE

UIColor *pcolor = [[UIColor alloc] initWithHue:1 saturation:0 brightness:0 alpha:1];
pcolor.pColorId = 2352;
pcolor.pIsAvailable = YES;
NSLog(@"\nClass: %@\nColor ID: %d\nIs Availabled: %@", 
      NSStringFromClass([pcolor class]), 
      pcolor.pColorId, 
      pcolor.pIsAvailable ? @"YES" : @"NO");
[pcolor release];