ios - 没有图像或内容获取的 UITableView 断断续续滚动

Question

所以我得到了这个 UITableView，它从内存中获取数据(已经预加载，滚动时没有请求，所有内容都在布局 View 之前加载)。每个单元格的高度都根据 UITextView 和自动布局中的文本量动态计算。这些单元格是从 Nib 加载的，并且重复使用单元格工作正常(至少我希望如此)。我在计算行高时使用 UITableViewAutomaticDimension，因此我不会像 iOS 8 之前那样强制单元格布局两次。

这是我填充单元格并计算高度的相关方法:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellType = [self reuseIdentifierForIndexPath:indexPath];

    if ([cellType isEqualToString:kLoadingCell])
        return kLoadingCellHeight;
    else if ([cellType isEqualToString:kOfflineCell])
        return kOfflineCellHeight;
    else if ([cellType isEqualToString:kFootprintListHeaderCell])
        return kHeaderCellHeight;
    else if ([cellType isEqualToString:kFootprintCellUnsynced])
        return kUnsyncedCellHeight;
    else if ([cellType isEqualToString:kShowFullTripCell])
        return kShowFullTripCellHeight;
    else if ([cellType isEqualToString:kFootprintOnMapCell])
        return kFootprintOnMapCellHeight;
    else
    {
        return UITableViewAutomaticDimension;
    }
}

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellType = [self reuseIdentifierForIndexPath:indexPath];

    if ([cellType isEqualToString:kLoadingCell])
        return kLoadingCellHeight;
    else if ([cellType isEqualToString:kOfflineCell])
        return kOfflineCellHeight;
    else if ([cellType isEqualToString:kFootprintListHeaderCell])
        return kHeaderCellHeight;
    else if ([cellType isEqualToString:kFootprintCellUnsynced])
        return kUnsyncedCellHeight;
    else if ([cellType isEqualToString:kShowFullTripCell])
        return kShowFullTripCellHeight;
    else if ([cellType isEqualToString:kFootprintOnMapCell])
        return kFootprintOnMapCellHeight;
    else
    {
        return UITableViewAutomaticDimension;
    }
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    NSString *cellType = [self reuseIdentifierForIndexPath:indexPath];

    if ([cellType isEqualToString:kLoadingCell])
    {
        UITableViewCell *loadingCell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:nil];
        loadingCell.tag = kLoadingCellTag;
        loadingCell.selectionStyle = UITableViewCellSelectionStyleNone;
        loadingCell.backgroundColor = loadingCell.contentView.backgroundColor = [UIColor clearColor];

        UIActivityIndicatorView *activityIndicatorView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
        activityIndicatorView.center = CGPointMake(tableView.frame.size.width / 2, 20);
        [loadingCell.contentView addSubview:activityIndicatorView];

        [activityIndicatorView startAnimating];

        return loadingCell;
    }
    else if ([cellType isEqualToString:kOfflineCell])
    {
        FPOfflineCell *offlineCell = [tableView dequeueReusableCellWithIdentifier:kOfflineCell];
        return offlineCell;
    }
    else if ([cellType isEqualToString:kFootprintListHeaderCell])
    {
        FPFootprintListHeaderCell *headerCell = [tableView dequeueReusableCellWithIdentifier:kFootprintListHeaderCell];
        [headerCell.syncButton addTarget:self action:@selector(syncButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        return headerCell;
    }
    else if ([cellType isEqualToString:kFootprintCellUnsynced])
    {
        FPFootprintCellUnsynced *unsyncedCell = [tableView dequeueReusableCellWithIdentifier:kFootprintCellUnsynced];
        unsyncedCell.footprint = self.map.footprintsNonSynced[[self unsyncedFootprintIndexForIndexPath:indexPath]];
        return unsyncedCell;
    }
    else if ([cellType isEqualToString:kShowFullTripCell])
    {
        FPShowFullTripCell *showFullTripCell = [tableView dequeueReusableCellWithIdentifier:kShowFullTripCell];
        return showFullTripCell;
    }
    else if ([cellType isEqualToString:kFootprintOnMapCell])
    {
        FPFootprintOnMapCell *footprintOnMapCell = [tableView dequeueReusableCellWithIdentifier:kFootprintOnMapCell];
        footprintOnMapCell.footprint = self.map.footprints[0];
        return footprintOnMapCell;
    }
    else
    {
        FPFootprint *footprint = self.map.footprints[[self footprintIndexForIndexPath:indexPath]];
        FootprintCell *cell = [tableView dequeueReusableCellWithIdentifier:kFootprintCell];
        cell.titleLabel.text = footprint.name;
        cell.dateLabel.text = footprint.displayDate;
        cell.textView.text = nil;
        if (footprint.text && footprint.text.length > 0) {
            if ([self.readmoreCache[@(footprint.hash)] boolValue]) {
                cell.textView.text = footprint.text;
            } else {
                cell.textView.text = [footprint.text stringByAppendingReadMoreAndLimitingToCharacterCount:300 screenWidth:tableView.frame.size.width];
            }
        } else {
            cell.hasText = NO;
        }
        cell.textView.markdownLinkTextViewDelegate = self;
        [cell.textView setNeedsDisplay];
        cell.isPrivate = footprint.isPrivate;
        [cell.likesAndCommentsView setLikesCount:footprint.likes andCommentsCount:footprint.comments];
        [cell.likesAndCommentsView setLiked:footprint.liked];
        [cell.likesAndCommentsView.likeButton addTarget:self action:@selector(likeButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        [cell.likesAndCommentsView.likesTextButton addTarget:self action:@selector(likesTextButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        [cell.likesAndCommentsView.commentButton addTarget:self action:@selector(commentButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        [cell.likesAndCommentsView.commentsTextButton addTarget:self action:@selector(commentsTextButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        [cell.detailButton addTarget:self action:@selector(detailButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        [cell.translateButton addTarget:self action:@selector(translateButtonPressed:) forControlEvents:UIControlEventTouchUpInside];
        if (footprint.canBeTranslated) {
            cell.translationStatus = footprint.translationState;
            if (footprint.translationState == FPFootprintTranslationStateTranslated) {
                cell.translatedTextView.text = footprint.translatedText;
            }
        } else {
            cell.translationStatus = FPFootprintTranslationStateNotAvailible;
        }
        cell.numberOfImages = 2;

        return cell;
    }
}

这是我的手机:

import UIKit

@objc class FootprintCell: UITableViewCell {

    var translationStatus: FPFootprintTranslationState = .NotTranslated {
        didSet {
            translateButton.hidden = true
            translateLoader.stopAnimating()
            translatedTextView.hidden = true
            translatedTextView.text = nil

            translatedTextView.addConstraint(translatedTextViewHeightConstraint)
            translationButtonHeightConstraint.constant = 0
            loaderHeightConstraint.constant = 0

            switch translationStatus {
            case .NotAvailible:
                break
            case .NotTranslated:
                translateButton.hidden = false
                translationButtonHeightConstraint.constant = translationButtonHeightConstraintConstant
            case .Translating:
                translateLoader.startAnimating()
                loaderHeightConstraint.constant = loaderHeightConstraintConstant
                translatedTextView.text = nil
            case .Translated:
                translatedTextView.hidden = false
                translatedTextView.removeConstraint(translatedTextViewHeightConstraint)
            }
        }
    }

    var isPrivate: Bool = false {
        didSet {
            privacyBar.hidden = !isPrivate
            privacyIcon.image = UIImage(named: isPrivate ? "ic_lock" : "ic_globe")
        }
    }

    var hasText: Bool = true {
        didSet {
            if hasText {
                textView.removeConstraint(textViewHeightConstraint)
            } else {
                textView.addConstraint(textViewHeightConstraint)
            }
        }
    }

    var numberOfImages: Int = 0 {
        didSet {
            if numberOfImages == 0 {
                imagesContainer.subviews.map { $0.removeFromSuperview() }
            } else if numberOfImages == 2 {
                twoImagesContainer = NSBundle.mainBundle().loadNibNamed("FootprintCellTwoImagesContainer", owner: nil, options: nil)[0] as? FootprintCellTwoImagesContainer
                twoImagesContainer?.setTranslatesAutoresizingMaskIntoConstraints(false)
                imagesContainer.addSubview(twoImagesContainer!)
                let views = ["foo" : twoImagesContainer!] as [NSString : AnyObject]
                imagesContainer.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[foo]|", options: .allZeros, metrics: nil, views: views))
                imagesContainer.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[foo]|", options: .allZeros, metrics: nil, views: views))
            }
        }
    }

    @IBOutlet private(set) weak var titleLabel: UILabel!
    @IBOutlet private(set) weak var dateLabel: UILabel!
    @IBOutlet private(set) weak var textView: FPForwardingTextView!
    @IBOutlet private(set) weak var likesAndCommentsView: FPLikesAndCommentsView!
    @IBOutlet private weak var privacyBar: UIView!
    @IBOutlet private weak var privacyIcon: UIImageView!
    @IBOutlet private(set) weak var detailButton: UIButton!
    @IBOutlet private(set) weak var translateButton: UIButton!
    @IBOutlet private weak var translateLoader: UIActivityIndicatorView!
    @IBOutlet private(set) weak var translatedTextView: FPForwardingTextView!
    @IBOutlet private(set) weak var imagesContainer: UIView!

    private(set) var twoImagesContainer: FootprintCellTwoImagesContainer?

    @IBOutlet private weak var translationButtonHeightConstraint: NSLayoutConstraint!
    @IBOutlet private weak var loaderHeightConstraint: NSLayoutConstraint!
    @IBOutlet private var translatedTextViewHeightConstraint: NSLayoutConstraint!
    @IBOutlet private var textViewHeightConstraint: NSLayoutConstraint!

    private var translationButtonHeightConstraintConstant: CGFloat!
    private var loaderHeightConstraintConstant: CGFloat!

    override func awakeFromNib() {
        super.awakeFromNib()

        textView.contentInset = UIEdgeInsets(top: -10, left: -5, bottom: 0, right: 0)
        textView.linkColor = UIColor(fromHexString: "0088CC")

        translatedTextView.contentInset = UIEdgeInsets(top: -10, left: -5, bottom: 0, right: 0)
        translatedTextView.linkColor = UIColor(fromHexString: "0088CC")

        privacyBar.backgroundColor = UIColor(patternImage: UIImage(named: "ic_privacy_bar"))

        translatedTextView.text = nil
        translatedTextView.hidden = true
        translateButton.hidden = true
        translationButtonHeightConstraintConstant = translationButtonHeightConstraint.constant
        loaderHeightConstraintConstant = loaderHeightConstraint.constant
        hasText = true
    }

    func layoutMargins() -> UIEdgeInsets {
        return UIEdgeInsetsZero
    }

    override func prepareForReuse() {
        super.prepareForReuse()
        numberOfImages = 0
        translationStatus = .NotAvailible
        hasText = true
    }

}

FootprintCellTwoImagesContainer 和 FPLikesAndCommentsView 从 Nibs 加载，目前不包含任何图像或加载任何内容，只是一些自动布局。

所以主要问题是，即使加载了整个 tableView 并且每个单元格都至少显示一次(因此应该有足够的单元格可以重复使用)，在向上或向下缓慢滚动单元格边框后，我得到一个小的跳跃(比如上下 5 个像素)。这在每台设备上都会发生，甚至在 6 Plus 上也是如此。

您知道问题出在哪里吗？我希望这不是我在 xibs 中的限制，至少 Interface Builder 不会在那里抛出警告......

Answer 1

我不太确定 UITableViewAutomaticDimension 是否适用于表格单元格。从文档...

You return this value from UITableViewDelegate methods that request dimension metrics when you want UITableView to choose a default value. For example, if you return this constant in the tableView:heightForHeaderInSection: or tableView:heightForFooterInSection:, UITableView uses a height that fits the value returned from tableView:titleForHeaderInSection: or tableView:titleForFooterInSection: (if the title is not nil).

没有提到表格 View 单元格。

所以我搜索了一下，发现了这个... more discussion on UITableViewAutomaticDimension...

它说的地方..

it will not work. UITableViewAutomaticDimension is not intended to be used to set the row height. Use rowHeight and specify your value or implement:

所以我认为你可能错了。