这是一个可行的解决方案：
它一直绕着圆圈，但你明白了，它看起来是一个渐变的笔触：
从宏开始：
#define DEGREES_TO_RADIANS(degrees) ((M_PI * degrees)/ 180)
UIImageView * shff = [UIImageView new];
[shff setImage:[UIImage imageNamed:@"REPLACE_WITH_YOUR_IMAGE"]];
[shff setBackgroundColor:[UIColor whiteColor]];
[shff setClipsToBounds:true];
[shff.layer setCornerRadius:SCREEN_HEIGHT/6];
[shff setFrame:CGRectMake(SCREEN_HEIGHT/3/2, 100, SCREEN_HEIGHT/3, SCREEN_HEIGHT/3)];
[self.view addSubview:shff];
int radius = shff.frame.size.width/2+7;
CAShapeLayer *arc = [CAShapeLayer layer];
arc.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(shff.center.x, shff.center.y) radius:radius startAngle:DEGREES_TO_RADIANS(-90) endAngle:DEGREES_TO_RADIANS(90) clockwise:YES].CGPath;
arc.fillColor = [UIColor clearColor].CGColor;
arc.strokeColor = [UIColor purpleColor].CGColor;
arc.lineWidth = 15;
CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
drawAnimation.duration = 45.0;
drawAnimation.repeatCount = 1.0;
drawAnimation.removedOnCompletion = NO;
drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
drawAnimation.toValue = [NSNumber numberWithFloat:1.0f];
drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
[arc addAnimation:drawAnimation forKey:@"drawCircleAnimation"];
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = self.view.frame;
gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor,(__bridge id)[UIColor blueColor].CGColor ];
gradientLayer.startPoint = CGPointMake(0,0.5);
gradientLayer.endPoint = CGPointMake(1,0.5);
[self.view.layer addSublayer:gradientLayer];
gradientLayer.mask = arc;
截图：
我刚刚更改了我的答案，所以现在它可以工作了，只需使用度数到弧度宏即可。另外，我只是在解决方案中添加了一个圆角线帽，并更改了开始和结束动画的 % 帧。现在应该可以顺利运行了。
我为 Sh%ts 和咯咯笑做了一个不同的解决方案。这是使用发射器层的较新解决方案：
-(void)doGradientoutline {
UIImageView * imageView = [UIImageView new];
[imageView setImage:[UIImage imageNamed:@"df"]];
[imageView setFrame:CGRectMake(SCREEN_WIDTH/2-imageView.image.size.width*3/2, SCREEN_HEIGHT/4, imageView.image.size.height*3, imageView.image.size.height*3)];
[imageView setClipsToBounds:true];
[imageView.layer setCornerRadius:imageView.frame.size.width/2];
[self.view addSubview:imageView];
int radius = imageView.frame.size.width/2+7;
CAShapeLayer *arc = [CAShapeLayer layer];
arc.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(imageView.center.x, imageView.center.y) radius:radius startAngle:DEGREES_TO_RADIANS(0) endAngle:DEGREES_TO_RADIANS(360) clockwise:YES].CGPath;
arc.fillColor = [UIColor clearColor].CGColor;
arc.strokeColor = [UIColor purpleColor].CGColor;
arc.lineWidth = 15;
[arc setLineCap:@"round"];
CAEmitterLayer * _myEmitter = [CAEmitterLayer layer];
_myEmitter.emitterPosition = CGPointMake(self.view.frame.size.width/2, self.view.frame.size.height/2);
_myEmitter.emitterSize = CGSizeMake(1.0,1);
_myEmitter.emitterMode = kCAEmitterLayerPoints;
_myEmitter.emitterShape = kCAEmitterLayerSphere;
_myEmitter.renderMode = kCAEmitterLayerOldestFirst;
_myEmitter.shadowOpacity = 0.0;
_myEmitter.shadowRadius = 0.0;
_myEmitter.shadowOffset = CGSizeMake(-10.0,-10);
_myEmitter.shadowColor = [[UIColor colorWithRed:1.00 green:1.00 blue:0.99 alpha:1.0] CGColor];
CAEmitterCell * _myCell = [CAEmitterCell emitterCell];
_myCell = [CAEmitterCell emitterCell];
_myCell.name = @"_myCell";
_myCell.beginTime = CACurrentMediaTime();
_myCell.birthRate = 80;
_myCell.lifetime = 8.0;
_myCell.color = [[UIColor colorWithRed:0.1000 green:0.00 blue:0.5000 alpha:1.00] CGColor];
_myCell.redSpeed = 1.10;
_myCell.blueSpeed = 1.10;
_myCell.alphaSpeed = 0;
_myCell.redRange = 0.0;
_myCell.blueRange = 0.0;
_myCell.alphaRange = 0.0;
_myCell.contents = (id)[[UIImage imageNamed:@"ffd.png"] CGImage];
_myCell.emissionRange = 0.00;
_myCell.emissionLatitude = 0.00;
_myCell.emissionLongitude = 0.00;
_myCell.velocity = 0.00;
_myCell.velocityRange = 0.00;
_myCell.spin = 2*M_PI;
_myCell.spinRange = 2*M_PI;
_myCell.scale = 1.5/ [[UIScreen mainScreen] scale];
_myCell.scaleSpeed = 0.00;
_myCell.scaleRange = 0.0;
_myEmitter.emitterCells = [NSArray arrayWithObject:_myCell];
CAKeyframeAnimation *particleAnimation = [CAKeyframeAnimation animationWithKeyPath:@"emitterPosition"];
[particleAnimation setPath:arc.path];
[particleAnimation setDuration:8.0];
[particleAnimation setRepeatCount:HUGE_VAL];
[particleAnimation setCalculationMode:kCAAnimationPaced];
[_myEmitter addAnimation:particleAnimation forKey:@"yourAnimation"];
CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
drawAnimation.duration = 1.50;
drawAnimation.repeatCount = 1.0;
drawAnimation.removedOnCompletion = NO;
drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
drawAnimation.toValue = [NSNumber numberWithFloat:1.f];
drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
[self.view.layer addSublayer:_myEmitter];
}
您必须下载此图像并将其存储在您的捆绑包中才能使其正常工作，这不是标准图像，它使用 Adobe Illustrator 使用了几层外发光，这是发射器发光的部分原因并更改颜色，只需单击下面的紫色模糊图像，您将右键单击并保存然后导入到您的项目中。在你的 viewDidAppear 中调用上面的方法可以无缝查看它是如何工作的，祝你好运：
新结果：