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，所有内容都在视图布局之前加载）。每个单元格的高度根据UITextView和Autolayout中的文本量动态计算。从Nib加载细胞并重复使用细胞正常工作（至少我希望如此）。我在计算行高时使用UITableViewAutomaticDimension，所以我不强制单元格布局两次，就像你在iOS 8之前那样做。

以下是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是从Nib加载的，目前不包含任何图像或加载任何内容，只有一些Autolayout。

所以主要问题是即使整个tableView被加载并且每个单元格至少显示一次（因此应该有足够的单元格可以重复使用），在缓慢地向上或向下滚动单元格边框后，我得到一个小跳跃（像上下5个像素）。这种情况发生在每台设备上，即使在6 Plus上也是如此。

问题出在哪里？我希望它不是我在xibs中的约束，至少Interface Builder不会在那里发出警告......

Answer 1

我不太确定UITableViewAutomaticDimension是用于表格单元格的。从文档......

当您希望UITableView选择默认值时，从UITableViewDelegate方法返回此值，该方法请求维度指标。例如，如果在tableView：heightForHeaderInSection：或tableView：heightForFooterInSection：中返回此常量，则UITableView使用的高度适合从tableView返回的值：titleForHeaderInSection：或tableView：titleForFooterInSection :(如果标题不是nil）。

没有提到tableview单元格。

所以我做了一个搜索，发现了这个...... more discussion on UITableViewAutomaticDimension...

它说的地方..

它不起作用。 UITableViewAutomaticDimension不用于设置行高。使用rowHeight并指定您的值或实现：

所以我认为你可能有这个错误。

Answer 2

OK之前的代码，原则。我有一个列中有4个标签的自定义单元格。顶部标签（label1）始终具有文本，底部标签（label4）也始终具有文本。标签2和3可以包含文本，可以是一个，也可以是两个。为了实现调整大小，我们使用了部分自动布局和部分委托方法（距离你的目标不远）

在“界面”构建器中，我们设置原型单元格的约束

Label1：领先，尾随，顶部，高度，宽度

标签2：前导，尾随，顶部，底部，高度，宽度

Label3：领先，尾随，顶部，底部，高度，宽度

Label4：领先，尾随，顶部，底部，高度，宽度

对于标签1和标签4（顶部和底部），我们将内容压缩电阻优先级垂直设置为“必需”（1000） 对于标签2和3 ，我们将内容压缩电阻优先级垂直设置为“低”（250）

这基本上意味着如果高度应该降低，首先折叠标签2和3以及折叠标签1和4。（您可能已经知道所有这些）您应该没有任何警告，并且限制所有正确添加的内容。（除非你知道它的作用，否则不要使用约束边距）

现在代码。

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
// Calls the sizing method to return a calculated height.
return [self heightForBasicCellAtIndexPath:indexPath];

}

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
//taken from interface builder. If all 4 labels have strings and not collapsed, this is the height the cell will be.
return 123.0f;

}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
// Yours has lots of case logic - 
// Mine is similar but I configure the properties of the custom cell elsewhere mainly so it can be used for sizing.
[self configureCell:cell atIndexPath:indexPath];
return cell;

}

- (void)configureCell:(MyJobCell *)cell atIndexPath:(NSIndexPath *)indexPath {

// my data source
MyCase *aCase = [_fetchedResultsController objectAtIndexPath:indexPath];

// setting the labels to match the case from data
cell.label1.text = aCase.name;
cell.label2.text = aCase.address;
cell.label3.text = aCase.postcode;
cell.label4.text = aCase.caseDescription;

}

- (CGFloat)heightForBasicCellAtIndexPath:(NSIndexPath *)indexPath {
// In here I create a cell and configure it with a cell identifier
static MyJobCell *sizingCell = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    sizingCell = [self.tableView dequeueReusableCellWithIdentifier:MyJobCellIdentifier];
});

// This configures the sizing cell labels with text values
[self configureCell:sizingCell atIndexPath:indexPath];

// This line calls the calculation. It fires the Auto Layout constraints on the cell,
// If label 2 and / or label 3 are empty, they will be collapsed to 0 height.
return [self calculateHeightForConfiguredSizingCell:sizingCell];

}

- (CGFloat)calculateHeightForConfiguredSizingCell:(MYJobCell *)sizingCell {

//Force the cell to update its constraints
[sizingCell setNeedsLayout];
[sizingCell layoutIfNeeded];

// Get the size of the 'squashed' cell and return it to caller
CGSize size = [sizingCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
return size.height;

}

这是我向你展示工作方法的最好方法。您必须进行调整，以便逻辑地满足您拥有的所有不同类型的自定义单元格。但除此之外，我认为这应该有所帮助。让我知道你是怎么过的。

UITableView不连贯滚动没有图像或内容提取

2 个答案: