如何使用“getHue：saturation：brightness：alpha：”？

问题描述

在iOS 5的UIColor中有这个方法：

There's this method in UIColor in iOS 5:

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

不知道我打算如何在代码中使用它。当然，我不需要说明每个组件，如果我想要从UIColor中获得。

But i don't understand how i'm meant to use that in code. Surely i don't need to be stating each of those components if i'm looking to get that out of the UIColor?

推荐答案

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 br>
getHue：saturation：brightness：alpha：返回一个bool，确定UIColor是否已被转换。

edit
getHue:saturation:brightness:alpha: returns a bool, determining, if the UIColor could had been converted at all.

例如：

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);

logs 0.000000 0.000000 -1.998918 0.000000 0 。最后的0是Bool，所以这是无效的，实际上亮度只能从0.0到1.0 ，但在这里它拥有一些随机的垃圾。

logs 0.000000 0.000000 -1.998918 0.000000 0. The last 0 is the Bool, so this is not valid, and actually brightness can only range from 0.0 to 1.0, but here it holds some random crap.

结论

代码应该是

conclusion
The code should be something like

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?
}

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