如何在 CALayer 中绘制径向渐变？

I know CAGradientLayer目前不支持径向渐变，只能选择kCAGradientLayerAxial.

我想要如下所示的东西：

我环顾四周寻找这个问题，发现有一种方法可以解决这个问题。但我并不清楚这些解释。所以我想知道是否可以使用绘制径向渐变CAGradientLayer如果是这样，那么该怎么做呢？

据我了解，你只需要一个绘制渐变的图层，并且CGContextDrawRadialGradient非常适合这种需求。并重申你所说的话，CAGradientLayer不支持径向渐变，对此我们无能为力，除了可以使用CALayer子类。

(注意：渐变绘制代码是取自这里 https://stackoverflow.com/questions/11421222/optimize-cgcontextdrawradialgradient-in-drawrect。这不是这个答案的目的。)

viewDidLoad:

GradientLayer *gradientLayer = [[GradientLayer alloc] init];
gradientLayer.frame = self.view.bounds;

[self.view.layer addSublayer:gradientLayer];

CALayer子类：

- (instancetype)init
{
    self = [super init];
    if (self) {
        [self setNeedsDisplay];
    }
    return self;
}

- (void)drawInContext:(CGContextRef)ctx
{

    size_t gradLocationsNum = 2;
    CGFloat gradLocations[2] = {0.0f, 1.0f};
    CGFloat gradColors[8] = {0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.0f,0.5f};
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, gradColors, gradLocations, gradLocationsNum);
    CGColorSpaceRelease(colorSpace);

    CGPoint gradCenter= CGPointMake(CGRectGetMidX(self.bounds), CGRectGetMidY(self.bounds));
    CGFloat gradRadius = MIN(self.bounds.size.width , self.bounds.size.height) ;

    CGContextDrawRadialGradient (ctx, gradient, gradCenter, 0, gradCenter, gradRadius, kCGGradientDrawsAfterEndLocation);


    CGGradientRelease(gradient);
}