CGContextRef context=UIGraphicsGetCurrentContext();    CGColorSpaceRef colorSp=CGColorSpaceCreateDeviceRGB();    CGFloat components[]={1.0,0.0,0.0,1.0,                        0,1,0,1,                        0,0,1,1                       };    CGFloat location[]={0.1,0.5,0.9};    CGGradientRef gradient=CGGradientCreateWithColorComponents(colorSp, components, location, 3);    //创建一直线，沿直线渐变//    CGContextDrawLinearGradient(context, gradient, CGPointMake(0, 50), CGPointMake(50, 150), 0);        CGContextDrawRadialGradient(context, gradient, CGPointMake(200, 300), 130, CGPointMake(100, 200), 60, 0);    //    CGContextStrokePath(context);        //圆筒    int j=10;    for (int i=60; i<270; i=i+10) {        j=j+5;        CGContextDrawRadialGradient(context, gradient, CGPointMake(150, i),j, CGPointMake(150, i+10),j+4, 0);    }