iOS 渐变色

实现渐变色的几种方式:

使用场景：背景渐变

1. 通过CAGradientLayer实现

// 1. 重写UIView的方法， 返回一个渐变图层
+ (Class)layerClass {
    return [CAGradientLayer class];
}
-  (void)configGradientLayer {
  // 颜色cgcolor
  NSArray *colors =  @[(id)[UIColor redColor].CGColor,
                           (id)[UIColor greenColor].CGColor];
    self.layer.colors = colors;
    // 设置渐变的方向 矢量 
    self.layer.startPoint = CGPointMake(0, 0);
    self.layer.endPoint = CGPointMake(1.0, 0.0);
}

使用场景：背景渐变， 文字渐变

2. 创建一个渐变的Image

+ (UIImage *)linearGradientImageWithSize:(CGSize)size
                                  colors:(NSArray<id>*)colors
                               locations:(CGFloat[])locations
                              startPoint:(CGPoint)startPoint
                                endPoint:(CGPoint)endPoint
{
    UIImage *resultImage = nil;
    //开启图片上下文
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    //创建路径
    UIBezierPath *path = [UIBezierPath bezierPathWithRect: CGRectMake(0,0,size.width,size.height)];
    //颜色
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGGradientRef gradient = CGGradientCreateWithColors(colorSpace, (__bridge CFArrayRef) colors, locations);
    //具体方向可根据需求修改
    CGContextSaveGState(context);
    CGContextAddPath(context, path.CGPath);
    CGContextClip(context);
    //画渐变
    CGContextDrawLinearGradient(context, gradient, startPoint, endPoint, 0);
    CGContextRestoreGState(context);
    //资源释放
    CGGradientRelease(gradient);
    CGColorSpaceRelease(colorSpace);
    //生成图片
    resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resultImage;
}

- (void)testButtonAddGradientBackground {
  NSArray *colors =  @[(id)[UIColor redColor].CGColor,
                           (id)[UIColor greenColor].CGColor];
    CGFloat locations[2] = {0.0, 1.0};
    UIImage *followImage = [self linearGradientImageWithSize:CGSizeMake(36, 36) colors:colors locations:locations startPoint:CGPointMake(0, 0) endPoint:CGPointMake(36, 0)];
// 设置按钮的背景
    [button setBackgroundImage:followImage forState:UIControlStateNormal];
          [button setImage:image forState:UIControlStateNormal];
}

- (void)testLabelTextGradientColor {
          NSArray *colors =  @[(id)[UIColor redColor].CGColor,
                           (id)[UIColor greenColor].CGColor];
        CGFloat locations[2] = {0.0, 1.0};
        UIImage *gradientImage = [self linearGradientImageWithSize:CGSizeMake(30,30) colors:colors locations:locations startPoint:CGPointMake(0, 0) endPoint:CGPointMake(30, 0)];
        [self.titleLabel.textColor = [UIColor colorWithPatternImage: gradientImage];
}