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，如果我想要从UIColor那里得到它，我不需要说明每个组件吗？

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

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

示例：

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，因为它有效

，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);

记录0.000000 0.000000 -1.998918 0.000000 0。最后的0是Bool，所以这是无效的，实际上是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

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CGFloat s，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：

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

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

2 个答案:

结论