近期某設計師喜歡上了用漸變色的背景.

發現Pokemon Go當中也使用了很多漸變色,覺得很喜歡Pokemon Go的UI設計.

漸變有線性漸變和徑向漸變,在iOS中實現漸變色可以用CAGradientLayer,或者用Quartz2D(平臺:Xcode7.2/iOS9.2).

• 1.使用CAGradientLayer實現線性漸變
  直接上代碼:
  CAGradientLayer *layer = [CAGradientLayer layer];
  layer.frame = self.view.bounds;
  //顏色分配:四個一組代表一種顏色(r,g,b,a)
  layer.colors = @[(__bridge id) [UIColor colorWithRed:55/255.0 green:222/255.0 blue:255/255.0 alpha:1.0].CGColor,
  (__bridge id) [UIColor colorWithRed:57/255.0 green:169/255.0 blue:213/255.0 alpha:1.0].CGColor];
  //起始點
  layer.startPoint = CGPointMake(0.5, 0.25);
  //結束點
  layer.endPoint = CGPointMake(0.5, 0.75);

        [self.view.layer addSublayer:layer];
  

對于起始點和結束點(0,0)為左下,(1,1)為右上.
實際效果是這樣的

• 2.使用Quartz2D實現徑向漸變
  上代碼:
  //新建子類,繼承UIVIew
  - (void)drawRect:(CGRect)rect {
  CGContextRef context = UIGraphicsGetCurrentContext();

        //1.Create CGColorSpaceRef
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
  
        //2.Create CGGradientRef
        //顏色分配:四個一組代表一種顏色(r,g,b,a)
        CGFloat components[8] = {55/255.0, 222/255.0, 255/255.0, 1.0,
                         57/255.0, 169/255.0 ,213/255.0, 1.0};
        //位置:每種顏色對應中心點位置,取0-1之間的float,默認起始點為(0,0)
        CGFloat locations[2] = {0, 1};
        //點數量:count為locations數量,size_t類型
        size_t count = 2;
        CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, count);
  
        //3.DrawRadialGradient
        /**漸變點:
         起始點
         結束點
         起始半徑
         結束半徑
         */
        CGPoint startCenter = CGPointMake(self.frame.size.width * 0.5, self.frame.size.height * 0.25);
        CGPoint endCenter = CGPointMake(self.frame.size.width * 0.5, self.frame.size.height * 0.25);
        CGFloat startRadius = 0;
        CGFloat endRadius = self.frame.size.height;
        CGContextDrawRadialGradient(context, gradient, startCenter, startRadius, endCenter, endRadius, kCGGradientDrawsAfterEndLocation);
  
        //4.Release
        CGColorSpaceRelease(colorSpace);
        colorSpace = NULL;
        CGGradientRelease(gradient);
        gradient = NULL;
    }
  

放效果圖:

用Quartz2D也可以實現線性漸變,方法類似.

由于筆者知識有限，如有錯誤，歡迎指出。