Add gradient border to UIView

UIView+UPGradientBorder.h

#import <UIKit/UIKit.h>

@interface UIView (UPGradientBorder)

- (void)up_setHorizontalGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth;
- (void)up_setVerticalGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth;
- (void)up_setGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth startPoint:(CGPoint)startPoint endPoint:(CGPoint)endPoint;
- (void)up_removeGradientBorder;

@end

UIView+UPGradientBorder.m

#import "UIView+UPGradientBorder.h"

static NSString* const kLayerNameGradientBorder = @"UPGradientBorderLayer";

@implementation UIView (UPGradientBorder)

- (void)up_setHorizontalGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth
{
    [self up_setGradientBorderWithColors:colors borderWidth:borderWidth startPoint:{0, 0.5} endPoint:{1, 0.5}];
}

- (void)up_setVerticalGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth
{
    [self up_setGradientBorderWithColors:colors borderWidth:borderWidth startPoint:{0.5, 0} endPoint:{0.5, 1}];
}

- (void)up_setGradientBorderWithColors:(NSArray<UIColor*>*)colors borderWidth:(CGFloat)borderWidth startPoint:(CGPoint)startPoint endPoint:(CGPoint)endPoint
{
    auto existedBorder = [self gradientBorderLayer];
    auto border = existedBorder ?: CAGradientLayer.layer;

    border.name = kLayerNameGradientBorder;
    border.frame = self.bounds;
    border.startPoint = startPoint;
    border.endPoint = endPoint;
    auto cgColors = [NSMutableArray array];
    for (UIColor* c in colors)
    {
        [cgColors addObject:((__bridge id)c.CGColor)];
    }
    border.colors = cgColors;

    auto mask = CAShapeLayer.layer;
    mask.path = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:0].CGPath;
    mask.fillColor = UIColor.clearColor.CGColor;
    mask.strokeColor = UIColor.whiteColor.CGColor;
    mask.lineWidth = borderWidth;

    border.mask = mask;

    auto exists = existedBorder != nil;
    if (!exists)
    {
        [self.layer addSublayer:border];
    }
}

- (void)up_removeGradientBorder
{
    [self.gradientBorderLayer removeFromSuperlayer];
}

- (CAGradientLayer*)gradientBorderLayer
{
    for (CALayer* l in self.layer.sublayers)
    {
        if ([l.name isEqualToString:kLayerNameGradientBorder])
        {
            return OBJC_DYNAMIC_CAST(l, CAGradientLayer);
        }
    }
    return nil;
}

@end