利用 CABasicAnimation 實現顏色的漸變動畫

- (void)doAnimation:(BOOL)hidden{
    CABasicAnimation *anim1 = [CABasicAnimation animationWithKeyPath:@"backgroundColor"];
    anim1.duration = 0.2;
    anim1.fromValue = hidden ? (__bridge id _Nullable)([UIColor whiteColor].CGColor) : (__bridge id _Nullable)([UIColor blackColor].CGColor);
    anim1.toValue = hidden ? (__bridge id _Nullable)([UIColor blackColor].CGColor) : (__bridge id _Nullable)([UIColor whiteColor].CGColor);
    //填充效果：動畫結束後，動畫將保持最後的表現狀態
    anim1.fillMode = kCAFillModeForwards;
    anim1.removedOnCompletion = NO;
    anim1.beginTime = 0.0f;
    [self.mainScrollView.layer addAnimation:anim1 forKey:@"backgroundColor"];
    
}