径向渐变：

- (void)drawRect:(CGRect)rect

{

CGContextRef ctx = UIGraphicsGetCurrentContext();

//创建一个RGB的颜色空间

CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();

//定义渐变颜色数组

CGFloat colors[] =

{

0.0f, 0.0f, 0.0f, 0.3f,

0.0f, 0.0f, 0.0f, 0.1f,

0.0f, 0.0f, 0.0f, 0.3f

};

const CGFloat locations[3] = { 0.0f, 0.5f, 1.0f };

//创建一个渐变的色值 1:颜色空间 2:渐变的色数组 3:位置数组,如果为NULL,则为平均渐变,否则颜色和位置一一对应 4:位置的个数

CGGradientRef _gradient = CGGradientCreateWithColorComponents(rgb, colors, locations, sizeof(colors)/(sizeof(colors[0])*4));

CGColorSpaceRelease(rgb);

//获得一个CGRect

//CGRect clip = CGRectInset(CGContextGetClipBoundingBox(ctx), 20.0, 20.0);

//剪切到合适的大小

//CGContextClipToRect(ctx, clip);

//定义起始点和终止点

CGPoint start = CGPointMake(CGRectGetMinX(self.bounds), CGRectGetMinY(self.bounds));

CGPoint end = CGPointMake(CGRectGetMinX(self.bounds), CGRectGetMaxY(self.bounds));

//绘制渐变, 颜色的0对应start点,颜色的1对应end点,第四个参数是定义渐变是否超越起始点和终止点

CGContextDrawLinearGradient(ctx, _gradient, start, end, kCGGradientDrawsBeforeStartLocation);

}

圆形辐射渐变

- (void)drawRect:(CGRect)rect

{

const CGFloat components[8] = { 0.0f, 0.0f, 0.0f, 0.3f, 0.0f, 0.0f, 0.0f, 0.7f };

const CGFloat locations[2] = { 0.0f, 1.0f };

CGColorSpaceRef space = CGColorSpaceCreateDeviceRGB();

CGGradientRef gradient = CGGradientCreateWithColorComponents(space, components, locations, 2);

CGColorSpaceRelease(space);

CGFloat x = CGRectGetMidX(self.bounds);

CGFloat y = CGRectGetMidY(self.bounds);

CGPoint point = CGPointMake(x, y);

CGFloat radius = MAX(x, y);

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextDrawRadialGradient(context, gradient, point, 0, point, radius, kCGGradientDrawsAfterEndLocation);

CGGradientRelease(gradient);

}