绘制渐变时崩溃

Question

我遇到了崩溃：

-[Not A Type retain]: message sent to deallocated instance 0x1e5ed7f0

---

void drawLinearGradient(CGContextRef context, CGRect rect, CGColorRef startColor, 
                                        CGColorRef  endColor)
{
    UIColor *start = [UIColor colorWithCGColor:startColor];
    UIColor *end = [UIColor colorWithCGColor:endColor];
}