ios画线的正确处理方式

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [UIColor lightGrayColor].CGColor);
    CGContextFillRect(context, CGRectMake(0, CGRectGetHeight(self.frame) - 0.5, CGRectGetWidth(self.frame), 0.5));
}