Uitableview 为什么cellForRowAtIndexPath有时会添加渐变层？

我有一个函数，看起来像这样：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
// instantiate the cell

if(indexPath.row >=4 && indexPath.row <=5)
{
[CustomTableCell addGradient];
}
}

---

我刚刚意识到iPhone/cocoa实际上是在重新使用内存中的现有单元格，以便cellForRowAtIndexpath绘制屏幕上显示的单元格。这就是为什么细胞仍然有我之前设置的梯度层。因此，我使用以下代码更新了stylecell函数，以删除存在的层：

- (void) styleCell
{
    if([self.layer.sublayers count] >0)
    {
        if([[self.layer.sublayers objectAtIndex:0] isKindOfClass:[CAGradientLayer class]])
        {
            [[self.layer.sublayers objectAtIndex:0] removeFromSuperlayer];
//            return;
        }
    }

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = self.bounds;

    gradient.colors = [NSArray arrayWithObjects:(id)[UIColor blueColor].CGColor, (id)[UIColor redColor].CGColor, nil];


    [self.layer insertSublayer:gradient atIndex:0];
}
@end

- (void) styleCell
{
    if([self.layer.sublayers count] >0)
    {
        if([[self.layer.sublayers objectAtIndex:0] isKindOfClass:[CAGradientLayer class]])
        {
            [[self.layer.sublayers objectAtIndex:0] removeFromSuperlayer];
//            return;
        }
    }

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = self.bounds;

    gradient.colors = [NSArray arrayWithObjects:(id)[UIColor blueColor].CGColor, (id)[UIColor redColor].CGColor, nil];


    [self.layer insertSublayer:gradient atIndex:0];
}
@end