给定一种颜色，获取颜色的A R G B值

#pragma mark - 获取颜色的 argb
- ( void )getRGBComponents:( CGFloat [ 4 ])components forColor:( UIColor *)color {
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB ();
    unsigned char resultingPixel[ 4 ];
    CGContextRef context = CGBitmapContextCreate (&resultingPixel,
                                                 1 ,
                                                 1 ,
                                                 8 ,
                                                 4 ,
                                                 rgbColorSpace,
                                                 ( CGBitmapInfo ) kCGImageAlphaPremultipliedLast );
    CGContextSetFillColorWithColor (context, [color CGColor ]);
    CGContextFillRect (context, CGRectMake ( 0 , 0 , 1 , 1 ));
    CGContextRelease (context);
    CGColorSpaceRelease (rgbColorSpace);
   
    for ( int component = 0 ; component < 4 ; component++) {
        components[component] = resultingPixel[component] / 255.0f ;
    }
}

使用：

// 获取线的颜色的 argb 值

        CGFloat components[ 4 ];
        [ self getRGBComponents :components forColor : self . drawView . strokeColor ];

component数组中保存的就是r,g,b,a的值了。