我如何使用"getHue:saturation:brightness:alpha:"？

Question

iOS 5中的UIColor中有这种方法:

- (BOOL)getHue:(CGFloat *)hue saturation:(CGFloat *)saturation brightness:(CGFloat *)brightness alpha:(CGFloat *)alpha

但我不明白我是如何在代码中使用它的.当然,如果我想从UIColor那里得到它,我当然不需要说明每个组件？

Answer 1

CGFloat hue;
CGFloat saturation;
CGFloat brightness;
CGFloat alpha;

[aColor getHue:&hue 
    saturation:&saturation 
    brightness:&brightness 
         alpha:&alpha];    
//now the variables hold the values

编辑
getHue:saturation:brightness:alpha:返回一个bool,确定是否可以转换UIColor.

例:

BOOL b = [[UIColor colorWithRed:.23 green:.42 blue:.9 alpha:1.0] getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha];
NSLog(@"%f %f %f %f %d", hue, saturation, brightness, alpha, b);

将记录0.619403 0.744444 0.900000 1.000000 1,因为它是有效的

而

BOOL b = [[UIColor colorWithPatternImage:[UIImage imageNamed:@"pattern.png"]] getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha];
NSLog(@"%f %f %f %f %d", hue, saturation, brightness, alpha, b);

日志0.000000 0.000000 -1.998918 0.000000 0.最后的0是Bool,所以这是无效的,实际上brightness can only range from 0.0 to 1.0,但这里有一些随机的废话.

结论
代码应该是这样的

CGFloat hue;
CGFloat saturation;
CGFloat brightness;
CGFloat alpha;

if([aColor getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha]){
    //do what ever you want to do if values are valid
} else {
    //what needs to be done, if converting failed? 
    //Some default values? raising an exception? return?
}

Answer 2

请注意,这四个参数是指针到CGFloatS,而不仅仅是值.这是标准的C传递引用.另请参阅以下Stack Overflow问题:

• 将返回的指针重写为输出参数
• 使用Objective-C中的引用传递
• 传出参数

举个例子:

CGFloat hue, saturation, brightness, alpha;
[myColor getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha];
// hue, saturation, brightness, and alpha are now set