colors 漸變的顏色
locations 顏色變化位置的取值范圍
startPoint 顏色漸變的起始位置:取值范圍在(0,0)~(1,1)之間
endPoint 顏色漸變的終點位置,取值范圍也是在(0,0)~(1,1)之間
補充下:startPoint & endPoint設(shè)置為(0,0)(1.0,0)代表水平方向漸變,(0,0)(0,1.0)代表豎直方向漸變

  CAGradientLayer * gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.button1.bounds;
    gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor,(__bridge id)[UIColor yellowColor].CGColor];
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(0, 1);
    gradientLayer.locations = @[@0,@1];
    [self.button1.layer addSublayer:gradientLayer];