CAGradientLayer *grad = [CAGradientLayer layer];
grad.colors = $array(ColRGBA2(1, 0, 0, 1), ColRGBA2(0, 1, 0, 1), ColRGBA2(0, 0, 1, 1), ColRGBA2(0, 0, 0, 0));
grad.startPoint = CGPointMake(0, 0);
grad.endPoint = CGPointMake(1, 0);
grad.colors = $array(ColRGBA2(1, 0, 0, 1), ColRGBA2(0, 1, 0, 1), ColRGBA2(0, 0, 1, 1), ColRGBA2(0, 0, 0, 0));
这个句子中有一个美元符号,这是什么意思?有没有相关链接可以提供?