iOS8使用Core Graphics实现渐变效果-Swift基础教程

转载

mb5ff590c45613d 2016-01-07 17:49:00

Core Graphics是一个强大的底层API,在这篇教程中我们主要使用Core Graphics来实现渐变效果,为了简单起见,我们采用线性渐变。线性渐变是从起点到终点颜色进行顺序渐变。教程在iOS8.1及Xcode6.1下编译通过。

打开Xcode,新建项目选择Single View Application,Product Name填写IOS8SwiftGradientsCoreGraphicsTutorial,Organization Name和Organization Identifier自行填写,选择Swift语言与iPhone设备。

项目增加一个新文件iOS->Source->Cocoa Touch Class,创建gradientView类并且继承于UIView

打开Storyboard,选中View然后打开Identity Inspector面板,将Custom Class选择为gradientView

打开gradientView.swift文件,修改drawRect方法如下：

// 1
      var currentContext = UIGraphicsGetCurrentContext()

      // 2
      CGContextSaveGState(currentContext);

      // 3
      var colorSpace = CGColorSpaceCreateDeviceRGB()

      // 4
      var startColor = UIColor.redColor();
      var startColorComponents = CGColorGetComponents(startColor.CGColor)
      var endColor = UIColor.blueColor();
      var endColorComponents = CGColorGetComponents(endColor.CGColor)

      // 5
      var colorComponents
        = [startColorComponents[0], startColorComponents[1], startColorComponents[2], startColorComponents[3], endColorComponents[0], endColorComponents[1], endColorComponents[2], endColorComponents[3]]

      // 6
      var locations:[CGFloat] = [0.0, 1.0]

      // 7
      var gradient = CGGradientCreateWithColorComponents(colorSpace,&colorComponents,&locations,2)

      var startPoint = CGPointMake(0, self.bounds.height)
      var endPoint = CGPointMake(self.bounds.width, self.bounds.height)

      // 8
      CGContextDrawLinearGradient(currentContext,gradient,startPoint,endPoint, 0)

      // 9
      CGContextRestoreGState(currentContext);