将UIViews添加到cell.contentView时，UITableView性能问题 [英] UITableView performance issues when adding UIViews to cell.contentView

问题描述

在我的 UITableViewCells 上使用某些子视图时，我遇到性能问题.在我不断滚动之后，它最终开始变得非常缓慢.

我要做的第一步是为每个单元格创建一个通用的 UIView ，从本质上讲，这是在白色单元格上创建一个带有阴影的圆形效果的白色单元格.这样做的性能似乎很正常，所以我不认为这是罪魁祸首.

这是我用来执行此操作的代码:

 <代码>-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{静态NSString * NewsCellIdentifer = @"NewsCellIdentifier";NewsItem * item = [self.newsArray objectAtIndex:indexPath.row];UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:NewsCellIdentifer];如果(cell == nil){单元格= [[UITableViewCell分配] initWithStyle:UITableViewCellStyleDefault重用标识符:NewsCellIdentifer];cell.contentView.backgroundColor = [UIColor clearColor];UIView * whiteRoundedCornerView = [[UIView alloc] initWithFrame:CGRectMake(10,10,300,100)];whiteRoundedCornerView.backgroundColor = [UIColor whiteColor];whiteRoundedCornerView.layer.masksToBounds = NO;whiteRoundedCornerView.layer.cornerRadius = 3.0;whiteRoundedCornerView.layer.shadowOffset = CGSizeMake(-1，1);whiteRoundedCornerView.layer.shadowOpacity = 0.5;[cell.contentView addSubview:whiteRoundedCornerView];[cell.contentView sendSubviewToBack:whiteRoundedCornerView];cell.layer.shouldRasterize = YES;cell.layer.rasterizationScale = [UIScreen mainScreen] .scale;cell.layer.opaque = YES;cell.opaque = YES;}[cell.contentView addSubview:[self NewsItemThumbnailView:item]];返回单元} 

以下是返回图形和文本的缩略图视图的方法:

 -(UIView *)NewsItemThumbnailView:(NewsItem *)项目{UIView * thumbNailMainView = [[UIView alloc] initWithFrame:CGRectMake(10，10，50，70)];UIImageView * thumbNail = [[UIImageView分配] initWithImage:[UIImage imageNamed:item.ThumbNailFileName]];thumbNail.frame = CGRectMake(10,10，45，45);UILabel * date = [[UILabel alloc] init];date.frame = CGRectMake(10，53，45，12);date.text = item.ShortDateString;date.textAlignment = NSTextAlignmentCenter;date.textColor = [BVColors WebDarkGrey];CGFloat fontSize = 10.0;date.font = [BVFont Museo:& fontSize];date.opaque =是;thumbNail.opaque =是;thumbNailMainView.opaque = YES;[thumbNailMainView addSubview:thumbNail];[thumbNailMainView addSubview:date];返回thumbNailMainView;} 

性能问题似乎是当我将缩略图视图添加到单元格时，因为当我注释掉该行时，我似乎没有它.缩略图信息是动态的，并且会随每个单元格而变化.对于在不降低性能的情况下应如何操作的任何建议，我将不胜感激.

解决方案

我最终利用了在以下stackoverflow帖子中找到的解决方案:

如何将Subview添加到cell.contentView?

基本上，当第一次初始化单元格时，我将按照Nishant的说明设置视图；但是，一旦单元被重用，我将提取需要更改的项目，例如UIImageView和UILabel.由于这些是指针，因此我可以在需要时修改自己需要的内容，并且性能又很快.这是我所做的缩写.

 <代码>-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{静态NSString * NewsCellIdentifer = @"NewsCellIdentifier";NewsItem * item = [self.newsArray objectAtIndex:indexPath.row];UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:NewsCellIdentifer];UIView * thumbNailMainView = [[UIView alloc] initWithFrame:CGRectMake(10，10，50，70)];UIImageView * thumbNail;UIView * textMainView = [[UIView分配] initWithFrame:CGRectMake(20,20,80,80)];UILabel * headerLabel = [[UILabel alloc] initWithFrame:CGRectMake(52，-5，70，20)];UILabel * teaserLabel = [[UILabel alloc] initWithFrame:CGRectMake(50,20，210，40)];UIView * newsItemCornerMainView = [[UIView alloc] initWithFrame:CGRectMake(255.7，55.2，55，55)]；UIImageView * cornerIconView;//如果该单元格不存在，则将其重新设置.如果(cell == nil){单元格= [[UITableViewCell分配] initWithStyle:UITableViewCellStyleDefault重用标识符:NewsCellIdentifer];//配置所有各种子视图.....//下面的示例//制作标题视图headerLabel.text = item.Title;CGFloat textfontSize = 16.0f;headerLabel.font = [BVFont Museo:& textfontSize];headerLabel.textColor = [BVColors WebBlue];headerLabel.textAlignment = NSTextAlignmentLeft;headerLabel.numberOfLines = 0;headerLabel.tag = 50;//制作预告片视图teaserLabel.text = item.Teaser;teaserLabel.numberOfLines = 0;CGFloat tfontSize = 13.0f;teaserLabel.textAlignment = NSTextAlignmentLeft;teaserLabel.textColor = [BVColors WebDarkGrey];teaserLabel.font = [BVFont HelveticaNeue:& tfontSize];[teaserLabel sizeToFit];teaserLabel.tag = 51;[textMainView addSubview:headerLabel];[textMainView sendSubviewToBack:headerLabel];[textMainView addSubview:teaserLabel];[cell.contentView addSubview:textMainView];....}thumbNail =(UIImageView *)[cell viewWithTag:47];[thumbNail setImage:[UIImage imageNamed:item.ThumbNailFileName]]；headerLabel =(UILabel *)[cell viewWithTag:50];headerLabel.text = item.Title;teaserLabel =(UILabel *)[cell viewWithTag:51];teaserLabel.text = item.Teaser;cornerIconView =(UIImageView *)[cell viewWithTag:48];[cornerIconView setImage:[UIImage imageNamed:item.CornerIconFileName]]；返回单元} 

I am experiencing performance problems when using some subviews on my UITableViewCells. After I keep scrolling it eventually starts getting very slow.

First step I am doing is creating a common UIView for every cell, essentially this is creating a white cell with a rounded effect on the cell with a shadow. The performance for this seems to be normal so I don't think it's the culprit.

Here is the code I am using to do this:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
        static NSString *NewsCellIdentifer = @"NewsCellIdentifier";


       NewsItem *item = [self.newsArray objectAtIndex:indexPath.row];


            UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:NewsCellIdentifer];

            if (cell == nil)
            {
                cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:NewsCellIdentifer];


                cell.contentView.backgroundColor = [UIColor clearColor];

                UIView *whiteRoundedCornerView = [[UIView alloc] initWithFrame:CGRectMake(10,10,300,100)];
                whiteRoundedCornerView.backgroundColor = [UIColor whiteColor];
                whiteRoundedCornerView.layer.masksToBounds = NO;
                whiteRoundedCornerView.layer.cornerRadius = 3.0;
                whiteRoundedCornerView.layer.shadowOffset = CGSizeMake(-1, 1);
                whiteRoundedCornerView.layer.shadowOpacity = 0.5;

                [cell.contentView addSubview:whiteRoundedCornerView];
                [cell.contentView sendSubviewToBack:whiteRoundedCornerView];

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

                cell.opaque = YES;    
            }

            [cell.contentView addSubview:[self NewsItemThumbnailView:item]];

            return cell;
}

Here is the method that returns the thumbnail view of the graphic and text:

- (UIView *) NewsItemThumbnailView:(NewsItem *)item
{
    UIView *thumbNailMainView = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 50, 70)];
    UIImageView *thumbNail = [[UIImageView alloc] initWithImage:[UIImage imageNamed:item.ThumbNailFileName]];
    thumbNail.frame = CGRectMake(10,10, 45, 45);
    UILabel *date = [[UILabel alloc] init];
    date.frame = CGRectMake(10, 53, 45, 12);
    date.text = item.ShortDateString;
    date.textAlignment = NSTextAlignmentCenter;
    date.textColor = [BVColors WebDarkGrey];
    CGFloat fontSize = 10.0;
    date.font = [BVFont Museo:&fontSize];

    date.opaque = YES;
    thumbNail.opaque = YES;
    thumbNailMainView.opaque = YES;


    [thumbNailMainView addSubview:thumbNail];
    [thumbNailMainView addSubview:date];

    return thumbNailMainView;
}

The performance problem seems to be when I add the thumbnail view to the cell because when I comment that line out, I don't seem to have it. The thumbnail information is dynamic and will change with each cell. I would appreciate any advice on how I should do this without degrading the performance.

解决方案

I ended up leveraging a solution found on this stackoverflow post:

How should I addSubview to cell.contentView?

Essentially when the cell is first initialized I am setting the view as mentioned by Nishant; however once the cell is reused I am extracting out the items I need to change, such as an UIImageView and then a UILabel. Since these are pointers I can modify just what I need when I need to and the performance is fast again. Here is a abbreviated version of what I did.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *NewsCellIdentifer = @"NewsCellIdentifier";

    NewsItem *item = [self.newsArray objectAtIndex:indexPath.row];
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:NewsCellIdentifer];


    UIView *thumbNailMainView = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 50, 70)];
    UIImageView *thumbNail;

    UIView *textMainView = [[UIView alloc] initWithFrame:CGRectMake(20,20,80,80)];
    UILabel *headerLabel = [[UILabel alloc] initWithFrame:CGRectMake(52,-5, 70, 20)];
    UILabel *teaserLabel = [[UILabel alloc] initWithFrame:CGRectMake(50,20, 210, 40)];

    UIView *newsItemCornerMainView = [[UIView alloc] initWithFrame:CGRectMake(255.7, 55.2, 55, 55)];
    UIImageView *cornerIconView;

    // If the cell doesn't existing go ahead and make it fresh.
    if (cell == nil)
    {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:NewsCellIdentifer];


        // Configure all the various subviews

         .....   //Sample below

        // Make the title view
        headerLabel.text = item.Title;
        CGFloat textfontSize = 16.0f;
        headerLabel.font = [BVFont Museo:&textfontSize];
        headerLabel.textColor = [BVColors WebBlue];
        headerLabel.textAlignment = NSTextAlignmentLeft;
        headerLabel.numberOfLines = 0;
        headerLabel.tag = 50;
        // Make the Teaser view
        teaserLabel.text = item.Teaser;
        teaserLabel.numberOfLines = 0;
        CGFloat tfontSize = 13.0f;
        teaserLabel.textAlignment = NSTextAlignmentLeft;
        teaserLabel.textColor = [BVColors WebDarkGrey];
        teaserLabel.font = [BVFont HelveticaNeue:&tfontSize];
        [teaserLabel sizeToFit];
        teaserLabel.tag = 51;
        [textMainView addSubview:headerLabel];
        [textMainView sendSubviewToBack:headerLabel];
        [textMainView addSubview:teaserLabel];
        [cell.contentView addSubview:textMainView];

        ....
    }

    thumbNail = (UIImageView *) [cell viewWithTag:47];
    [thumbNail setImage:[UIImage imageNamed:item.ThumbNailFileName]];

    headerLabel = (UILabel *) [cell viewWithTag:50];
    headerLabel.text = item.Title;
    teaserLabel = (UILabel *) [cell viewWithTag:51];
    teaserLabel.text = item.Teaser;

    cornerIconView = (UIImageView *) [cell viewWithTag:48];
    [cornerIconView setImage:[UIImage imageNamed:item.CornerIconFileName]];

    return cell;
}

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