获取颜色分量

#import <UIKit/UIKit.h>

@interface UIColor(ColorComponents)
- (CGColorSpaceModel) colorSpaceModel;
- (CGFloat) red;
- (CGFloat) green;
- (CGFloat) blue;
- (CGFloat) alpha;
@end

@implementation UIColor (ColorComponents)

- (CGColorSpaceModel) colorSpaceModel {
    return CGColorSpaceGetModel(CGColorGetColorSpace(self.CGColor));
}

- (CGFloat) red {
    const CGFloat *c = CGColorGetComponents(self.CGColor);
    return c[0];
}

- (CGFloat) green {
    const CGFloat *c = CGColorGetComponents(self.CGColor);
    if ([self colorSpaceModel] == kCGColorSpaceModelMonochrome)
        return c[0];
    return c[1];
}

- (CGFloat) blue {
    const CGFloat *c = CGColorGetComponents(self.CGColor);
    if ([self colorSpaceModel] == kCGColorSpaceModelMonochrome)
        return c[0];
    return c[2];
}

- (CGFloat) alpha {
    const CGFloat *c = CGColorGetComponents(self.CGColor);
    return c[CGColorGetNumberOfComponents(self.CGColor) - 1];
}

@end