ios - UITableViewCell 首次加载时未正确换行文本，但在屏幕上和屏幕外滚动时会正确换行

Question

我正在关注这个 thread 的答案关于使用具有动态高度的 UITableViewCell。这是 link to the great GitHub solution for iOS7 .

该示例在 iOS7 中适用于我，但是当我在 iOS6 中运行它时，第一个单元格没有正确换行。

只有在我滚动屏幕的单元格并重新打开后，环绕才看起来正确。

这是我的代码，我所做的任何更改都带有以下注释，以便它可以在 iOS6 中运行

// *** Added/Removed for iOS6

表格 View 单元格

#import "RJTableViewCell.h"

#define kLabelHorizontalInsets 20.0f

@interface RJTableViewCell ()

@property (nonatomic, assign) BOOL didSetupConstraints;

@end

@implementation RJTableViewCell

- (id)initWithStyle:(UITableViewCellStyle)style reuseIdentifier:(NSString *)reuseIdentifier
{
    self = [super initWithStyle:style reuseIdentifier:reuseIdentifier];
    if (self) {
        self.titleLabel = [[UILabel alloc] initWithFrame:CGRectZero];
        [self.titleLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.titleLabel setLineBreakMode:NSLineBreakByTruncatingTail];
        [self.titleLabel setNumberOfLines:1];
        [self.titleLabel setTextAlignment:NSTextAlignmentLeft];
        [self.titleLabel setTextColor:[UIColor blackColor]];
        [self.titleLabel setBackgroundColor:[UIColor clearColor]];

        self.bodyLabel = [[UILabel alloc] initWithFrame:CGRectZero];
        [self.bodyLabel setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self.bodyLabel setContentCompressionResistancePriority:UILayoutPriorityRequired forAxis:UILayoutConstraintAxisVertical];
        [self.bodyLabel setLineBreakMode:NSLineBreakByTruncatingTail];
        [self.bodyLabel setNumberOfLines:0];
        [self.bodyLabel setTextAlignment:NSTextAlignmentLeft];
        [self.bodyLabel setTextColor:[UIColor darkGrayColor]];
        [self.bodyLabel setBackgroundColor:[UIColor clearColor]];

        [self.contentView addSubview:self.titleLabel];
        [self.contentView addSubview:self.bodyLabel];

        [self updateFonts];
    }

    return self;
}

- (void)updateConstraints
{
    [super updateConstraints];

    if (self.didSetupConstraints) return;

    [self.contentView addConstraint:[NSLayoutConstraint
                                     constraintWithItem:self.titleLabel
                                     attribute:NSLayoutAttributeLeading
                                     relatedBy:NSLayoutRelationEqual
                                     toItem:self.contentView
                                     attribute:NSLayoutAttributeLeading
                                     multiplier:1.0f
                                     constant:kLabelHorizontalInsets]];

    [self.contentView addConstraint:[NSLayoutConstraint
                                     constraintWithItem:self.titleLabel
                                     attribute:NSLayoutAttributeTop
                                     relatedBy:NSLayoutRelationEqual
                                     toItem:self.contentView
                                     attribute:NSLayoutAttributeTop
                                     multiplier:1.0f
                                     constant:(kLabelHorizontalInsets / 2)]];

    [self.contentView addConstraint:[NSLayoutConstraint
                                     constraintWithItem:self.titleLabel
                                     attribute:NSLayoutAttributeTrailing
                                     relatedBy:NSLayoutRelationEqual
                                     toItem:self.contentView
                                     attribute:NSLayoutAttributeTrailing
                                     multiplier:1.0f
                                     constant:-kLabelHorizontalInsets]];

    //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    [self.contentView  addConstraint:[NSLayoutConstraint
                                      constraintWithItem:self.bodyLabel
                                      attribute:NSLayoutAttributeLeading
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.contentView
                                      attribute:NSLayoutAttributeLeading
                                      multiplier:1.0f
                                      constant:kLabelHorizontalInsets]];

    [self.contentView  addConstraint:[NSLayoutConstraint
                                      constraintWithItem:self.bodyLabel
                                      attribute:NSLayoutAttributeTop
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.titleLabel
                                      attribute:NSLayoutAttributeBottom
                                      multiplier:1.0f
                                      constant:(kLabelHorizontalInsets / 4)]];

    [self.contentView  addConstraint:[NSLayoutConstraint
                                      constraintWithItem:self.bodyLabel
                                      attribute:NSLayoutAttributeTrailing
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.contentView
                                      attribute:NSLayoutAttributeTrailing
                                      multiplier:1.0f
                                      constant:-kLabelHorizontalInsets]];

    [self.contentView  addConstraint:[NSLayoutConstraint
                                      constraintWithItem:self.bodyLabel
                                      attribute:NSLayoutAttributeBottom
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.contentView
                                      attribute:NSLayoutAttributeBottom
                                      multiplier:1.0f
                                      constant:-(kLabelHorizontalInsets / 2)]];

    self.didSetupConstraints = YES;
}

- (void)updateFonts
{
    self.titleLabel2.font = [UIFont systemFontOfSize:16.0f]; // *** Added for iO6
    self.bodyLabel.font = [UIFont systemFontOfSize:12.0f]; // *** Added for iO6
    //    self.titleLabel.font = [UIFont preferredFontForTextStyle:UIFontTextStyleHeadline]; // *** Removed for iO6
    //    self.bodyLabel.font = [UIFont preferredFontForTextStyle:UIFontTextStyleCaption2]; // *** Removed for iO6
}

表格 View Controller

#import "RJTableViewController.h"
#import "RJModel.h"
#import "RJTableViewCell.h"

static NSString *CellIdentifier = @"CellIdentifier";

@interface RJTableViewController ()

@property (strong, nonatomic) RJModel *model;

// This property is used to work around the constraint exception that is thrown if the
// estimated row height for an inserted row is greater than the actual height for that row.
// See: https://github.com/caoimghgin/TableViewCellWithAutoLayout/issues/6
@property (assign, nonatomic) BOOL isInsertingRow;

@end

@implementation RJTableViewController

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
        self.title = @"Table View Controller";
        self.model = [[RJModel alloc] init];
        [self.model populateDataSource];
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    [self.tableView registerClass:[RJTableViewCell class] forCellReuseIdentifier:CellIdentifier];

    self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemTrash target:self action:@selector(clear:)];

    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addRow:)];
}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [self.tableView reloadData]; // *** Added for iOS6

    // *** Removed for iOS6
    //    [[NSNotificationCenter defaultCenter] addObserver:self
    //                                             selector:@selector(contentSizeCategoryChanged:)
    //                                                 name:UIContentSizeCategoryDidChangeNotification
    //                                               object:nil];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];

    [self.tableView reloadData]; // *** Added for iOS6

    // *** Removed for iOS6
    //    [[NSNotificationCenter defaultCenter] removeObserver:self
    //                                                    name:UIContentSizeCategoryDidChangeNotification
    //                                                  object:nil];
}


- (void)contentSizeCategoryChanged:(NSNotification *)notification
{
    [self.tableView reloadData];
}

- (void)clear:(id)sender
{
    NSMutableArray *rowsToDelete = [NSMutableArray new];
    for (NSUInteger i = 0; i < [self.model.dataSource count]; i++) {
        [rowsToDelete addObject:[NSIndexPath indexPathForRow:i inSection:0]];
    }

    self.model = [[RJModel alloc] init];

    [self.tableView deleteRowsAtIndexPaths:rowsToDelete withRowAnimation:UITableViewRowAnimationAutomatic];

    [self.tableView reloadData];
}

- (void)addRow:(id)sender
{
    [self.model addSingleItemToDataSource];

    self.isInsertingRow = YES;

    NSIndexPath *lastIndexPath = [NSIndexPath indexPathForRow:[self.model.dataSource count] - 1 inSection:0];
    [self.tableView insertRowsAtIndexPaths:@[lastIndexPath] withRowAnimation:UITableViewRowAnimationAutomatic];

    self.isInsertingRow = NO;
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [self.model.dataSource count];
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    RJTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath];

    [cell updateFonts];

    NSDictionary *dataSourceItem = [self.model.dataSource objectAtIndex:indexPath.row];

    cell.titleLabel.text =  [dataSourceItem valueForKey:@"title"];
    cell.bodyLabel.text = [dataSourceItem valueForKey:@"body"];

    // Make sure the constraints have been added to this cell, since it may have just been created from scratch
    [cell setNeedsUpdateConstraints];

    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    RJTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    [cell updateFonts];

    NSDictionary *dataSourceItem = [self.model.dataSource objectAtIndex:indexPath.row];
    cell.titleLabel.text =  [dataSourceItem valueForKey:@"title"];
    cell.bodyLabel.text = [dataSourceItem valueForKey:@"body"];

    [cell setNeedsUpdateConstraints];
    [cell updateConstraintsIfNeeded];

    // Do the initial layout pass of the cell's contentView & subviews
    [cell.contentView setNeedsLayout];
    [cell.contentView layoutIfNeeded];

    // Since we have multi-line labels, set the preferredMaxLayoutWidth now that their width has been determined,
    // and then do a second layout pass so they can take on the correct height
    cell.bodyLabel.preferredMaxLayoutWidth = CGRectGetWidth(cell.bodyLabel.frame);
    [cell.contentView layoutIfNeeded];

    CGFloat height = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;

    return height;
}

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    if (self.isInsertingRow) {
        // A constraint exception will be thrown if the estimated row height for an inserted row is greater
        // than the actual height for that row. In order to work around this, we return the actual height
        // for the the row when inserting into the table view.
        // See: https://github.com/caoimghgin/TableViewCellWithAutoLayout/issues/6
        return [self tableView:tableView heightForRowAtIndexPath:indexPath];
    } else {
        return 500.0f;
    }
}

@end

这是一个before和 after我所看到的是否有用。

知道发生了什么事吗？我很感激任何见解。

Answer 1

根据@Wain 的建议，我尝试将所有代码从 heightForRowAtIndexPath 移动到 cellForRowAtIndexPath 并且成功了。我想我需要设置 cell.bodyLabel.preferredMaxLayoutWidth = CGRectGetWidth(cell.bodyLabel.frame)。

我将所有代码都移到了“cellForRowAtIndexPath”中，并让“heightForRowAtIndexPath”调用它来获取高度。现在我不确定为什么它在 iOS7 而不是 iOS6 中很好，但我仍在弄清楚一些自动布局的东西。

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    RJTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    [cell updateFonts];

    NSDictionary *dataSourceItem = [self.model.dataSource objectAtIndex:indexPath.row];
    cell.titleLabel2.text =  [dataSourceItem valueForKey:@"title"];
    cell.bodyLabel.text = [dataSourceItem valueForKey:@"body"];

    [cell setNeedsUpdateConstraints];
    [cell updateConstraintsIfNeeded];

    // Do the initial layout pass of the cell's contentView & subviews
    [cell.contentView setNeedsLayout];
    [cell.contentView layoutIfNeeded];

    // Since we have multi-line labels, set the preferredMaxLayoutWidth now that their width has been determined,
    // and then do a second layout pass so they can take on the correct height
    cell.bodyLabel.preferredMaxLayoutWidth = CGRectGetWidth(cell.bodyLabel.frame);
    [cell.contentView layoutIfNeeded];

    return cell;
}

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
    RJTableViewCell *cell = [self tableView:tableView cellForRowAtIndexPath:indexPath];

    CGFloat height = [cell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;

    return height;
}