1

我只是不明白这里发生了什么。

我有一个 UITableView ，其中每个单元格都包含一些子视图，并且一切正常。不幸的是，性能很糟糕，滚动太不稳定了。我读到也许你可以继承 UITableViewCell 并且这可以帮助提高性能，但我不确定如何实现或实施另一个解决问题的解决方案。我已经在下面发布了 tableView 的委托方法，任何帮助将不胜感激！

- (UITableViewCell *)tableView:(UITableView *)tableView
     cellForRowAtIndexPath:(NSIndexPath *)indexPath {


static NSString *CellIdentifier = @"Cell";
UIImageView* imageView;
UILabel* ttitle;
UILabel* ttitle2;
UILabel* ttitle3;
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];

    // Configure cell:
    // *** This section should configure the cell to a state independent of
    //  whatever row or section the cell is in, since it is only executed
    //  once when the cell is first created.


    imageView=[[UIImageView alloc]initWithFrame:CGRectMake(10.0, 11.0, 50.0, 50.0)];
    [imageView setContentMode:UIViewContentModeScaleAspectFill];
    imageView.layer.masksToBounds=YES;
    imageView.layer.cornerRadius=5.0;
    imageView.tag=1;
    [cell.contentView addSubview:imageView];

    ttitle = [[[UILabel alloc] initWithFrame:CGRectMake(70.0, 7.0, 200, 20)] autorelease];
    ttitle.textColor= [UIColor blackColor];
    ttitle.numberOfLines=1;
    ttitle.tag=69;
    ttitle.backgroundColor=[UIColor clearColor];
    ttitle.font=[UIFont fontWithName:@"Arial Bold" size:15.0];
    [cell.contentView addSubview:ttitle];

    if (indexPath.row==0) {

        CGSize size=[[[data objectAtIndex:indexPath.row] valueForKey:@"content"] sizeWithFont:[UIFont systemFontOfSize:14.0f] constrainedToSize:CGSizeMake(265.0f, CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping];
        ttitle2 = [[[UILabel alloc] initWithFrame:CGRectMake(70.0, 27.5, 200, size.height)] autorelease];
        ttitle2.textColor= [UIColor darkGrayColor];
        ttitle2.backgroundColor=[UIColor clearColor];
        ttitle2.numberOfLines=0;
        ttitle2.tag=70;
        ttitle2.textAlignment = NSTextAlignmentLeft;
        ttitle2.lineBreakMode=NSLineBreakByWordWrapping;
        ttitle2.font=[UIFont fontWithName:@"Arial" size:14.0];
        [cell.contentView addSubview:ttitle2];

        ttitle3 = [[[UILabel alloc] initWithFrame:CGRectMake(70.0, ttitle2.frame.origin.y+ttitle2.frame.size.height-8.0, 210, 40)] autorelease];
        ttitle3.textColor= [UIColor darkGrayColor];
        ttitle3.backgroundColor=[UIColor clearColor];
        ttitle3.numberOfLines=1;
        ttitle3.tag=71;
        ttitle3.textAlignment = NSTextAlignmentLeft;
        ttitle3.lineBreakMode=NSLineBreakByWordWrapping;
        ttitle3.font=[UIFont fontWithName:@"Arial" size:11.0];
        [cell.contentView addSubview:ttitle3];


    }
    else{

        CGSize size=[[[data objectAtIndex:indexPath.row] valueForKey:@"content"] sizeWithFont:[UIFont systemFontOfSize:14.0f] constrainedToSize:CGSizeMake(265.0f, CGFLOAT_MAX) lineBreakMode:NSLineBreakByWordWrapping];
        ttitle2 = [[[UILabel alloc] initWithFrame:CGRectMake(70.0, 27.0, 200, size.height)] autorelease];
        ttitle2.textColor= [UIColor darkGrayColor];
        ttitle2.backgroundColor=[UIColor clearColor];
        ttitle2.numberOfLines=0;
        ttitle2.tag=70;
        ttitle2.textAlignment = NSTextAlignmentLeft;
        ttitle2.lineBreakMode=NSLineBreakByWordWrapping;
        ttitle2.font=[UIFont fontWithName:@"Arial" size:14.0];
        [cell.contentView addSubview:ttitle2];


        ttitle3 = [[[UILabel alloc] initWithFrame:CGRectMake(70.0, ttitle2.frame.origin.y+ttitle2.frame.size.height-9.0, 210, 40)] autorelease];
        ttitle3.textColor= [UIColor darkGrayColor];
        ttitle3.backgroundColor=[UIColor clearColor];
        ttitle3.numberOfLines=1;
        ttitle3.tag=71;
        ttitle3.textAlignment = NSTextAlignmentLeft;
        ttitle3.lineBreakMode=NSLineBreakByWordWrapping;
        ttitle3.font=[UIFont fontWithName:@"Arial" size:11.0];
        [cell.contentView addSubview:ttitle3];

    }


}
else {
    imageView = (UIImageView *) [cell viewWithTag:1];
    ttitle=( UILabel *) [cell viewWithTag:69];
    ttitle2=( UILabel *) [cell viewWithTag:70];
    ttitle3=( UILabel *) [cell viewWithTag:71];
}

//STUFFOUTSIDE

// Customize cell:
// *** This section should customize the cell depending on what row or section
//  is passed in indexPath, since this is executed every time this delegate method
//  is called.



imageView.image=[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:[[data objectAtIndex:indexPath.row] valueForKey:@"thumbnail"]]]];

[ttitle setText:[[data objectAtIndex:indexPath.row] valueForKey:@"name"]];
[ttitle2 setText:[[data objectAtIndex:indexPath.row] valueForKey:@"content"]];

NSString* first=[[[data objectAtIndex:indexPath.row] valueForKey:@"hashtag"] stringByAppendingString:@"     "];
NSString* second =[first stringByAppendingString:[[data objectAtIndex:indexPath.row] valueForKey:@"place"]];
NSString* third=[second stringByAppendingString:@"        "];
NSString* fourth=[third stringByAppendingString:@"¤ "];
NSString* conversion=[[[data objectAtIndex:indexPath.row] valueForKey:@"counter"] stringValue];
NSString* fifth=[fourth stringByAppendingString:conversion];
[ttitle3 setText:fifth];

return cell;

}

4

2 回答 2

6

您正在从 URL 同步获取数据以获取每个单元格的图像。这意味着对于每个单元格，您都会阻塞主线程，直到从 Internet 获取数据。

您必须在后台线程上异步加载图像，并在加载图像时更新单元格。有很多关于此的博客文章。

更新：
无法判断图像 URL 是否是本地的，但我假设它是远程 URL，并且图像未存储在您的应用程序中。

于 2013-03-03T19:18:21.493 回答
3

有很多问题会导致延迟，但在这种情况下我看到了三个可能的原因：

  1. 除非绝对需要，否则单元格子视图（您的标签等）的背景颜色不应清晰。这会杀死滚动性能。

  2. 如果在 imageView 中设置的图像尺寸不正确并且必须缩放，这将导致严重滞后。如果是这种情况，您要么需要保存适当大小的图像以在表格中显示，要么异步加载它们，以便表格滚动而无需等待图像加载。

  3. 正如 Fabian 在下面的评论中提到的那样，由于您是从 Web 下载这些图像，因此您肯定希望异步加载图像。每次显示一个单元格时，它都必须等待图像下载，然后才能显示下一个单元格。这是您现在使用此代码时遇到的最大问题。以下问题有几个不同的选择： iOS - Asynchronous Image Downloading

于 2013-03-03T19:13:48.883 回答