不能子类UIColor？

Question

我正在尝试将UIColor子类化,我似乎无法弄清楚什么是错的.

在我的PColor.h中

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

......在我的PColor.m中

#import "PColor.h"

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

在实例化PColor对象时,我得到:

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

我错过了什么吗？提前致谢.

Answer 1

UIColor是类集群使用类别中的关联引用来添加属性!UIColor返回的所有自定义init方法UIColor*都不是,id所以你不能轻易地子类,UIColor也不应该尝试.

的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

的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

用法

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];

Answer 2

从UIColor类参考:

大多数开发人员不需要子类化UIColor.如果您需要支持其他颜色空间或颜色模型,那么唯一可能需要这样做的时间.

你应该使用Category.例如:

@interface UIColor (PColor)
    - (BOOL) isAvailable;
    - (int) colorId;
@end

在实现文件中:

@implementation UIColor (PColor)

    - (BOOL)isAvailable {
        // do what you want to do
        // return your BOOL
    }

    - (int)colorId  {
        // do what you want to do
        // return id of color
    }

@end