eu quero fazer um arco com o uso deCAGradientLayer de tal maneira: -

20% do arco tem a mesma cor única e outros 80% do arco têm um gradiente de duas cores. Eu já tentei manualmentelocations startPoint endPoint propriedade deCAGradientLayer mas não conseguiu o sucesso e já passou por tutoriais, mas de alguma forma não conseguiu entender o conceito adequadamente. resolva meu problema com uma descrição clara dele.

// for beizier path
- (UIBezierPath *)samplePath
{
    UIBezierPath *path = [UIBezierPath bezierPath];

   path = [UIBezierPath bezierPath];
    [path addArcWithCenter:CGPointMake(200, 200) radius:30.0f startAngle:(3*M_PI)/4 endAngle:M_PI/4   clockwise:YES];
     path.lineWidth = 30;
    [[UIColor redColor] setStroke];
    // [[UIColor colorWithRed:arc4random() green:arc4random() blue:arc4random() alpha:1.0] setFill];
    [path stroke];

    return path;
}

- (void)startAnimation
{
    CAShapeLayer *shapeLayer;
    if (self.pathLayer == nil)
    {
        shapeLayer = [CAShapeLayer layer];

        shapeLayer.path = [[self samplePath] CGPath];
        shapeLayer.strokeColor = [[UIColor redColor] CGColor];
        shapeLayer.fillColor = nil;
        shapeLayer.lineWidth = 30;
        self.pathLayer = shapeLayer;
    }

    [self animationBasic];
    [self gradientLayer:shapeLayer];


}
-(void)animationBasic
{
    CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    pathAnimation.duration = 3.0;
    pathAnimation.fromValue = @(0.0f);
    pathAnimation.toValue = @(1.0f);
    [self.pathLayer addAnimation:pathAnimation forKey:@"strokeEnd"];
}

-(void)gradientLayer:(CAShapeLayer *)shapelayer
{

    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.frame;
    gradientLayer.colors = @[(__bridge id)[UIColor yellowColor].CGColor,(__bridge id)[UIColor redColor].CGColor ];
    gradientLayer.locations = [NSArray arrayWithObjects:
                               [NSNumber numberWithFloat:0.5f],
                               [NSNumber numberWithFloat:1.0f],
                               nil];
    //    gradientLayer.startPoint = CGPointMake(0,1);
    //    gradientLayer.endPoint = CGPointMake(1,1);
    [self.layer addSublayer:gradientLayer];
    gradientLayer.mask = shapelayer;

}