ios - 在 cellForItemAtIndexPath 中创建带有 NSTextAttachment 的 NSMutableAttributedString 是一个坏主意(性能或设计方面)吗？

Question

我正在我的 Collection View 的 cellForItemAtIndexPath 方法中创建 NSMutableAttributedString。我正在使用 NSTextAttachment 在文本中嵌入图像。

这是个坏主意吗？目前滚动性能似乎不错，但我不确定是否有更好的方法？将所有 NSMutableAttributedString 缓存在 NSMutableDictionary 中对于第二次滚动会更好吗？

使用 cellForRowAtIndexPath 也可以将相同的问题应用于 UITableview。

代码:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    CellView *cell = [collectionView dequeueReusableCellWithReuseIdentifier:[CellView reuseIdentifier] forIndexPath:indexPath];

    NSTextAttachment *attachment = [[NSTextAttachment alloc] init];
    attachment.image = [UIImage imageNamed:@"eye"];
    attachment.bounds = CGRectMake(0, -2.5, 14,14);
    NSAttributedString *attachmentString = [NSAttributedString attributedStringWithAttachment:attachment];

    NSMutableAttributedString *myString= [[NSMutableAttributedString alloc] initWithString:@""];
    [myString appendAttributedString:attachmentString];

    [myString appendAttributedString:[[NSMutableAttributedString alloc] initWithString:@" 19K    "]];

    NSTextAttachment *attachment2 = [[NSTextAttachment alloc] init];
    attachment2.image = [UIImage imageNamed:@"heart"];
    attachment2.bounds = CGRectMake(0, -2.5, 14,14);
    NSAttributedString *attachmentString2 = [NSAttributedString attributedStringWithAttachment:attachment2];

    [myString appendAttributedString:attachmentString2];

    [myString appendAttributedString:[[NSMutableAttributedString alloc] initWithString:@" 13K    "]];

    [myString enumerateAttribute:NSFontAttributeName inRange:(NSRange){0,[myString length]} options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:^(id value, NSRange range, BOOL *stop) {
        [myString addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"AvenirNext-Medium" size:12] range:range];
        [myString addAttribute:NSForegroundColorAttributeName value:[UIColor colorWithWhite:1 alpha:1] range:range];
    }];



    NSMutableAttributedString *titletext= [[NSMutableAttributedString alloc] initWithString:[self checkIfBig:indexPath]?[NSString stringWithFormat:@"\nThe Underground Railway"]:[NSString stringWithFormat:@"\nPink Oasis"]];

    [titletext enumerateAttribute:NSFontAttributeName inRange:(NSRange){0,[titletext length]} options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:^(id value, NSRange range, BOOL *stop) {
        [titletext addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"AvenirNext-Medium" size:24] range:range];
        [titletext addAttribute:NSForegroundColorAttributeName value:[UIColor whiteColor] range:range];
    }];

    [myString appendAttributedString:titletext];

    if ([self checkIfBig:indexPath]){
        NSMutableAttributedString *subtitletext= [[NSMutableAttributedString alloc] initWithString:@"\nLorem Ipsum is simply dummy text of the printing and typesetting industry."];

        [subtitletext enumerateAttribute:NSFontAttributeName inRange:(NSRange){0,[subtitletext length]} options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:^(id value, NSRange range, BOOL *stop) {
            [subtitletext addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"AvenirNext-Medium" size:14] range:range];
            [subtitletext addAttribute:NSForegroundColorAttributeName value:[UIColor whiteColor] range:range];
        }];
        [myString appendAttributedString:subtitletext];
    };

    if ([self checkIfBig:indexPath]){
        NSMutableAttributedString *subtitletext= [[NSMutableAttributedString alloc] initWithString:@"\n\n#HORROR #BLOOD"];

        [subtitletext enumerateAttribute:NSFontAttributeName inRange:(NSRange){0,[subtitletext length]} options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:^(id value, NSRange range, BOOL *stop) {
            [subtitletext addAttribute:NSFontAttributeName value:[UIFont fontWithName:@"AvenirNext-MediumItalic" size:14] range:range];
            [subtitletext addAttribute:NSForegroundColorAttributeName value:[UIColor whiteColor] range:range];
        }];
        [myString appendAttributedString:subtitletext];
    };

    cell.titleLabel.attributedText=myString;


    return cell;
}

Answer 1

作为一般规则，您的数据应该在加载 TableView 或 Collection View 之前组装一次。在您当前的代码中，当用户来回滚动时，您会一遍又一遍地重新创建相同的数据。这是非常低效的。

您的所有数据都应该在一个数组中(如果您有多个部分，则应在数组数组中)。您的 cellForRow|ItemAtIndexPath 应该只是从数组中获取一个对象，并且应该使用该对象的属性来填充单元格。

如果您有很多行或某些数据更昂贵，您可以通过按需创建某些数据元素并缓存它们来改进上述内容，这样您仍然只创建一次。

正确完成后，您问题中的 cellForItemAtIndexPath 应该少于 5 行代码。