- (void)drawRect:(CGRect)rect
{//1.获取绘图的上下文CGContextRef context = UIGraphicsGetCurrentContext();//线性渐变
    [self drawLinarGradient:context];//径向渐变
    [self drawRadialGradient:context];
}

-(void)drawLinarGradient:(CGContextRef) context
{//2.创建一个渐变//2.1 创建一个颜色空间CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();//2.2 设置颜色//设置开始颜色UIColor *startColor = [UIColor redColor];const CGFloat *startColorComponents = CGColorGetComponents([startColor CGColor]);//设置中间颜色UIColor *midColor = [UIColor greenColor];const CGFloat *midColorComponents = CGColorGetComponents([midColor CGColor]);//设置结束颜色UIColor *endColor = [UIColor blueColor];const  CGFloat *endColorComponents = CGColorGetComponents([endColor CGColor]);//颜色分量的强度值的数组CGFloat components[12] = {startColorComponents[0],startColorComponents[1],startColorComponents[2],startColorComponents[3],midColorComponents[0],midColorComponents[1],midColorComponents[2],midColorComponents[3],endColorComponents[0],endColorComponents[1],endColorComponents[2],endColorComponents[3]};//渐变系数(程度)CGFloat locations[3] = {0.0,0.5,1.0};//创建渐变(参数：颜色空间、颜色分量强度值数组、渐变系数数组、设置的渐变系数个数)CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, 3);//3.在上下文中画渐变(参数：上下文、渐变、开始点、结束点、渐变模式,默认为0)CGContextDrawLinearGradient(context, gradient, CGPointMake(100, 100), CGPointMake(100, 200), 0);//渐变模式：//kCGGradientDrawsAfterEndLocation      //向内发散//kCGGradientDrawsBeforeStartLocation   //向外发散//4.对creat创建的对象必须清理(避免内存泄露)
    CGColorSpaceRelease(colorSpace);CGGradientRelease(gradient);
}

-(void)drawRadialGradient:(CGContextRef) context
{//2.创建一个渐变//2.1 创建一个颜色空间CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();//2.2 设置开始颜色和结束颜色UIColor *startColor = [UIColor redColor];const CGFloat *startColorComponents = CGColorGetComponents([startColor CGColor]);UIColor *endColor = [UIColor whiteColor];const  CGFloat *endColorComponents = CGColorGetComponents([endColor CGColor]);//颜色分量的强度值数组CGFloat components[8] = {startColorComponents[0],startColorComponents[1],startColorComponents[2],startColorComponents[3],endColorComponents[0],endColorComponents[1],endColorComponents[2],endColorComponents[3]};

    //渐变系数数组
    CGFloat locations[2] = {0.0,1.0}; //创建渐变对象(参数：颜色空间、颜色分量的强度值数组、渐变系数数组、设置的渐变系数个数)CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace, components, locations, 2);//3.画渐变(参数：上下文、渐变对象、起点、径向半径、终点、径向半径、渐变模式)  CGContextDrawRadialGradient(context, gradient, CGPointMake(200, 400), 20, CGPointMake(200, 400), 40, kCGGradientDrawsBeforeStartLocation);

    //渐变模式：//kCGGradientDrawsAfterEndLocation      //向外发散//kCGGradientDrawsBeforeStartLocation   //向里发散

    //4.清理
    CGColorSpaceRelease(colorSpace);CGGradientRelease(gradient);
}