效果：

源碼很簡單，直接上代碼：

    // gradientLayer
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = CGRectMake(0, 0, self.view.width, 68);
    gradientLayer.position = self.view.center;
    gradientLayer.colors = @[(__bridge id)[UIColor blackColor].CGColor,
                                (__bridge id)[UIColor whiteColor].CGColor,
                                (__bridge id)[UIColor blackColor].CGColor];
    gradientLayer.locations = @[@0.25,@0.5,@0.75];
    gradientLayer.startPoint = CGPointMake(0, 0);
    gradientLayer.endPoint = CGPointMake(1, 0);
    [self.view.layer addSublayer:gradientLayer];
    
    // unlockLabel
    self.unlockLabel = [[UILabel alloc] initWithFrame:gradientLayer.bounds];
    _unlockLabel.textAlignment = NSTextAlignmentCenter;
    _unlockLabel.text = @"滑動來解鎖 >>";
    _unlockLabel.font = [UIFont boldSystemFontOfSize:28];
    _unlockLabel.textColor = [UIColor colorWithWhite:0 alpha:0.8];
    gradientLayer.mask = _unlockLabel.layer;
    
    // animation
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"locations"];
    animation.fromValue = @[@0,@0,@0.25];
    animation.toValue = @[@0.75,@1,@1];
    animation.repeatCount = MAXFLOAT;
    animation.duration = 2.5f;
    [gradientLayer addAnimation:animation forKey:nil];

源碼已經(jīng)放在GitHub：https://github.com/Fendouzhe/LRAnimations，有興趣的歡迎下載查看，有幫助可以star，謝謝！