UIView+BFRShimmering.m

UIView+BFRShimmering.m

//
//  UIView+BFRShimmer.h
//  BFRUtils
//
//  Created by Jordan Morgan on 8/14/18.
//  Copyright © 2018 Buffer. All rights reserved.
//

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface UIView (BFRShimmer)

@property (strong, nonatomic, readonly, nonnull) CAGradientLayer *gradient;
@property (strong, nonatomic, readonly, nonnull) CABasicAnimation *shimmerAnimation;

- (void)startShimmering;
- (void)startShimmeringWithRepitions:(NSInteger)reps;
- (void)endShimmering;

@end

NS_ASSUME_NONNULL_END


//
//  UIView+BFRShimmer.m
//  BFRUtils
//
//  Created by Jordan Morgan on 8/14/18.
//  Copyright © 2018 Buffer. All rights reserved.
//

#import "UIView+BFRShimmer.h"
#import <objc/runtime.h>

static NSString * const BFR_SHIMMER_KEY = @"bfr.Shimmering.animationKey";

@implementation UIView (BFRShimmer)

#pragma mark - Dynamic Properties

static const void *GradientKey = &GradientKey;
static const void *AnimationKey = &AnimationKey;

- (CAGradientLayer *)gradient {
    CAGradientLayer *returnVal = objc_getAssociatedObject(self, GradientKey);
    
    if (!returnVal) {
        returnVal = [CAGradientLayer new];
        objc_setAssociatedObject(self, GradientKey, returnVal, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    
    return returnVal;
}

- (CABasicAnimation *)shimmerAnimation {
    CABasicAnimation *returnVal = objc_getAssociatedObject(self, AnimationKey);
    
    if (!returnVal) {
        returnVal = [CABasicAnimation animationWithKeyPath:@"position"];
        objc_setAssociatedObject(self, AnimationKey, returnVal, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    
    return returnVal;
}

#pragma mark - Public API

- (void)startShimmeringWithRepitions:(NSInteger)reps {
    [CATransaction begin];
    [CATransaction setCompletionBlock:^{
        [self endShimmering];
    }];
    
    UIColor *lightColor = [[UIColor whiteColor] colorWithAlphaComponent:0.1];
    UIColor *darkColor = [[UIColor blackColor] colorWithAlphaComponent:1.0];
    
    CGFloat length = CGRectGetWidth(self.layer.bounds);
    CGFloat extraDistance = length + 1.0f * 0.4f;
    CGFloat fullShimmerLength = length * 3.0f + extraDistance;
    CGFloat travelDistance = length * 2.0f + extraDistance;
    CGFloat highlightOutsideLength = 0.0 / 2.0;
    CGFloat startPoint = (length + extraDistance) / fullShimmerLength;
    CGFloat endPoint = travelDistance / fullShimmerLength;
    
    self.gradient.bounds = CGRectMake(0.0, 0.0, fullShimmerLength, CGRectGetHeight(self.layer.bounds));
    self.gradient.position = CGPointMake(-travelDistance, 0.0);
    self.gradient.anchorPoint = CGPointZero;
    self.gradient.startPoint = CGPointMake(startPoint, 0.0);
    self.gradient.endPoint = CGPointMake(endPoint, 0.0);
    self.gradient.locations = @[@(highlightOutsideLength), @(0.5), @(1.0 - highlightOutsideLength)];
    self.gradient.colors = @[(id)darkColor.CGColor, (id)lightColor.CGColor, (id)darkColor.CGColor];
    
    self.shimmerAnimation.duration = 1.0;
    self.shimmerAnimation.repeatCount = reps > 0 ? reps : INFINITY;
    self.shimmerAnimation.toValue = [NSValue valueWithCGPoint:CGPointZero];
    
    [self.gradient addAnimation:self.shimmerAnimation forKey:BFR_SHIMMER_KEY];
    self.layer.mask = self.gradient;
    
    [CATransaction commit];
}
- (void)startShimmering {
    [self startShimmeringWithRepitions:0];
}

- (void)endShimmering {
    [self.layer.mask removeAnimationForKey:BFR_SHIMMER_KEY];
    self.layer.mask = nil;
    [self.layer setNeedsDisplay];
}

@end