Question

这是我用来生成UITableViewCell的代码。我正在iOS6 / iOS7中测试。如果我删除有关UIImageView的代码，UITableView滚动就好了。但是随着UIImageView它的滞后和痉挛。我正在寻找一些解决方案来解决滞后问题。提前谢谢。

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
    {
        static NSString *CellIdentifier = @"BubbleCell";
        UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
        UILabel *label;
        UIImageView *bubbleLeft;
        UIImageView *bubbleRight;

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

            label = [[UILabel alloc] init];
            label.tag = 1;

            NSString *fileLeft = [[NSBundle mainBundle] pathForResource:@"chatBubbleGray.png" ofType:nil];
            NSString *fileRight = [[NSBundle mainBundle] pathForResource:@"chatBubbleBlue.png" ofType:nil];

    UIImage
    *bubbleImageLeft = [[
    UIImage imageWithContentsOfFile:fileLeft] resizableImageWithCapInsets:UIEdgeInsetsMake(20, 22, 20, 22)];

    UIImage
    *bubbleImageRight = [[
    UIImage imageWithContentsOfFile:fileRight] resizableImageWithCapInsets:UIEdgeInsetsMake(20, 22, 20, 22)];

            bubbleLeft = [[UIImageView alloc] initWithFrame:CGRectMake(10, 10, 10, 10)];
            [bubbleLeft setImage:bubbleImageLeft];
            bubbleLeft.tag=2;
            bubbleRight = [[UIImageView alloc] initWithFrame:CGRectMake(320 - 20, 10, 10, 10)];
            [bubbleRight setImage:bubbleImageRight];
            bubbleRight.tag=3;

            [cell addSubview:bubbleLeft];
            [cell addSubview:bubbleRight];
            [cell addSubview:label];

        }else{
            label = (UILabel *)[cell viewWithTag:1];
            bubbleLeft = (UIImageView *)[cell viewWithTag:2];
            bubbleRight = (UIImageView *)[cell viewWithTag:3];
        }


    // set frame to largest size you want

        label.numberOfLines = 0;
        label.
    backgroundColor = [UIColor clearColor];
        label.
    text
    = [[[
    currentDictionary objectAtIndex:indexPath.row] objectForKey:@"string"] stringByReplacingOccurrencesOfString:@"\\n" withString:@"\n"];

        CGSize maximumLabelSize = CGSizeMake(296, FLT_MAX);

        CGSize expectedLabelSize = [label.text sizeWithFont:label.font constrainedToSize:maximumLabelSize lineBreakMode:label.lineBreakMode];

        if (indexPath.row%2==0) {
            bubbleRight.hidden = YES;
            bubbleLeft.hidden = NO;
            bubbleLeft.frame = CGRectMake(10, 10, expectedLabelSize.width+20, expectedLabelSize.height+20);

            label.frame = CGRectMake(
                                     20, 20,
                                     expectedLabelSize.width, expectedLabelSize.height);

        }else{
            bubbleLeft.hidden = YES;
            bubbleRight.hidden = NO;

            bubbleRight.frame = CGRectMake(320 - expectedLabelSize.width - 30, 10, expectedLabelSize.width+20, expectedLabelSize.height+20);

            label.frame = CGRectMake(
                                     320 - expectedLabelSize.width - 20, 20,
                                     expectedLabelSize.width, expectedLabelSize.height);
        }



    // Configure the cell...

        return cell;
    }

编辑：

进一步检查代码显示滞后实际上是由这段代码引起的： bubbleLeft.frame = CGRectMake(10, 10, expectedLabelSize.width+20, expectedLabelSize.height+20);

Answer 1

似乎resizableImage导致了我之前所说的滞后。问题是我试图使用这段代码：

UIImage imageWithContentsOfFile:fileLeft] resizableImageWithCapInsets:UIEdgeInsetsMake(20, 22, 20, 22)];

是

的图片

47x36。

这意味着我的帽子负向翻转可拉伸部分导致滞后。作为进一步的信息，resizableImageWithCapInsets:可以通过留出1px x 1px可伸缩区域来实现最佳性能。

Answer 2

您可以做的一件简单事情是使用UIImages而不是imageNamed:创建imageWithContentsOfFile:。 imageNamed:通常只会从第一个磁盘加载图像，然后对其进行缓存，而imageWithContentsOfFile:将每隔时间转到磁盘。

如果这不能帮助您获得所需的性能，则可能必须将图像加载过程移至另一个执行线程。

在UITableView中使用UIImageView和[UIImage resizableImageWithCapInsets]会导致延迟

2 个答案: