渐变色需求：（因为UIButton, UILabel, UITextField等均为UIView子视图，因此以下方法均可行）

• (void)changeColors:(UIView *)myView{

  CAGradientLayer *_gradLayer = [CAGradientLayer layer];
  NSArray *colors = [NSArray arrayWithObjects:
  (id)[[UIColor colorWithWhite:0 alpha:1] CGColor],
  (id)[[UIColor colorWithWhite:0 alpha:0.8] CGColor],
  (id)[[UIColor colorWithWhite:0 alpha:0.6] CGColor],
  nil];
  [_gradLayer setColors:colors];
  //渐变起止点，point表示向量
  [_gradLayer setStartPoint:CGPointMake(1.0f, 0.0f)];
  [_gradLayer setEndPoint:CGPointMake(0.0f, 0.0f)];
  [_gradLayer setFrame:myView.bounds];
  [myView.layer setMask:_gradLayer];
  }

//设置导航栏渐变色
typedef NS_ENUM(NSInteger, IHGradientChangeDirection) {
IHGradientChangeDirectionLevel,
IHGradientChangeDirectionVertical,
IHGradientChangeDirectionUpwardDiagonalLine,
IHGradientChangeDirectionDownDiagonalLine,
};

• (UIColor *)saj_colorGradientChangeWithSize:(CGSize)size
  direction:(IHGradientChangeDirection)direction
  startColor:(UIColor *)startcolor
  endColor:(UIColor *)endColor {

  if (CGSizeEqualToSize(size, CGSizeZero) || !startcolor || !endColor) {
  return nil;
  }

  CAGradientLayer *gradientLayer = [CAGradientLayer layer];
  gradientLayer.frame = CGRectMake(0, 0, size.width, size.height);

  CGPoint startPoint = CGPointZero;
  if (direction == IHGradientChangeDirectionDownDiagonalLine) {
  startPoint = CGPointMake(0.0, 1.0);
  }
  gradientLayer.startPoint = startPoint;

  CGPoint endPoint = CGPointZero;
  switch (direction) {
  case IHGradientChangeDirectionLevel:
  endPoint = CGPointMake(1.0, 0.0);
  break;
  case IHGradientChangeDirectionVertical:
  endPoint = CGPointMake(0.0, 1.0);
  break;
  case IHGradientChangeDirectionUpwardDiagonalLine:
  endPoint = CGPointMake(1.0, 1.0);
  break;
  case IHGradientChangeDirectionDownDiagonalLine:
  endPoint = CGPointMake(1.0, 0.0);
  break;
  default:
  break;
  }
  gradientLayer.endPoint = endPoint;

  gradientLayer.colors = @[(__bridge id)startcolor.CGColor, (__bridge id)endColor.CGColor];
  UIGraphicsBeginImageContext(size);
  [gradientLayer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage*image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return [UIColor colorWithPatternImage:image];
  }