UITableView 由于阴影和边框而滞后

我有以下代码来向 UITableViewCell 的背景添加边框颜色和阴影。我的问题是这段代码会导致 tableView 本身出现巨大的滞后。

请你告诉我如何优化我的代码，防止 UITableView 的滞后？

if ([cell viewWithTag:012] == nil && comment.isReply == NO) {
    UIImageView *iv = [[[UIImageView alloc] initWithFrame:frame] autorelease];
    [iv setImage:[UIImage imageNamed:@"paper"]];
    [iv setTag:012];
    [cell insertSubview:iv atIndex:0];

    [iv.layer setBorderWidth:1.0];
    [iv.layer setBorderColor:[[UIColor whiteColor] CGColor]];

    [iv.layer setShadowColor:[[UIColor blackColor] CGColor]];
    [iv.layer setShadowOffset:CGSizeMake(0, 1)];
    [iv.layer setShadowOpacity:0.75];

}

else if ([cell viewWithTag:012] == nil && comment.isReply == YES) {

    frame.origin.x += 35;

    UIImageView *iv = [[[UIImageView alloc] initWithFrame:frame] autorelease];
    [iv setImage:[UIImage imageNamed:@"paper"]];
    [iv setTag:012];
    [cell insertSubview:iv atIndex:0];

    UIImage *arrow = [UIImage imageNamed:@"arrow"];
    UIImageView *ivs = [[[UIImageView alloc] initWithFrame:CGRectMake(-12, ([cell frame].size.width / 2) + ([arrow size].width/2) , arrow.size.width, arrow.size.height)] autorelease];
    [cell addSubview:ivs];

    [iv.layer setBorderWidth:1.0];
    [iv.layer setBorderColor:[[UIColor whiteColor] CGColor]];

    [iv.layer setShadowColor:[[UIColor blackColor] CGColor]];
    [iv.layer setShadowOffset:CGSizeMake(0, 0)];
    [iv.layer setShadowOpacity:0.75];

}

除了此处的其他优化建议之外，还指定shadowPath在你的CALayer将提高阴影绘制性能。你可以用这样的东西来确定阴影的路径......

iv.layer.shadowPath = [UIBezierPath bezierPathWithRect:iv.bounds].CGPath;

您可能还想查看shouldRasterizeCALayer 上的位。这会导致图层被预渲染为位图。如果您选择此路线，请确保还提供与您的设备匹配的 rasterizationScale。

cell.layer.shouldRasterize = YES;
cell.layer.rasterizationScale = [UIScreen mainScreen].scale;