UITableView dynamic cell heights only correct after some scrolling

问题

I have a UITableView with a custom UITableViewCell defined in a storyboard using auto layout. The cell has several multiline UILabels.

The UITableView appears to properly calculate cell heights, but for the first few cells that height isn't properly divided between the labels. After scrolling a bit, everything works as expected (even the cells that were initially incorrect).

- (void)viewDidLoad {
    [super viewDidLoad]
    // ...
    self.tableView.rowHeight = UITableViewAutomaticDimension;
}


- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    TableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"TestCell"];
    // ...
    // Set label.text for variable length string.
    return cell;
}

Is there anything that I might be missing, that is causing auto layout not to be able to do its job the first few times?

I've created a sample project which demonstrates this behaviour.

回答1:

I don't know this is clearly documented or not, but adding [cell layoutIfNeeded] before returning cell solves your problem.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    TableViewCell *cell = [self.tableView dequeueReusableCellWithIdentifier:@"TestCell"];
    NSUInteger n1 = firstLabelWordCount[indexPath.row];
    NSUInteger n2 = secondLabelWordCount[indexPath.row];
    [cell setNumberOfWordsForFirstLabel:n1 secondLabel:n2];

    [cell layoutIfNeeded]; // <- added

    return cell;
}

回答2:

This worked for me when other similar solutions did not:

override func didMoveToSuperview() {
    super.didMoveToSuperview()
    layoutIfNeeded()
}

This seems like an actual bug since I am very familiar with AutoLayout and how to use UITableViewAutomaticDimension, however I still occasionally come across this issue. I'm glad I finally found something that works as a workaround.

回答3:

Adding [cell layoutIfNeeded] in cellForRowAtIndexPath does not work for cells that are initially scrolled out-of-view.

Nor does prefacing it with [cell setNeedsLayout].

You still have to scroll certain cells out and back into view for them to resize correctly.

This is pretty frustrating since most devs have Dynamic Type, AutoLayout and Self-Sizing Cells working properly — except for this annoying case. This bug impacts all of my "taller" table view controllers.

回答4:

I had same experience in one of my projects.

Why it happens?

Cell designed in Storyboard with some width for some device. For example 400px. For example your label have same width. When it loads from storyboard it have width 400px.

Here is a problem:

tableView:heightForRowAtIndexPath: called before cell layout it's subviews.

So it calculated height for label and cell with width 400px. But you run on device with screen, for example, 320px. And this automatically calculated height is incorrect. Just because cell's layoutSubviews happens only after tableView:heightForRowAtIndexPath: Even if you set preferredMaxLayoutWidth for your label manually in layoutSubviews it not helps.

My solution:

1) Subclass UITableView and override dequeueReusableCellWithIdentifier:forIndexPath:. Set cell width equal to table width and force cell's layout.

- (UITableViewCell *)dequeueReusableCellWithIdentifier:(NSString *)identifier forIndexPath:(NSIndexPath *)indexPath {
    UITableViewCell *cell = [super dequeueReusableCellWithIdentifier:identifier forIndexPath:indexPath];
    CGRect cellFrame = cell.frame;
    cellFrame.size.width = self.frame.size.width;
    cell.frame = cellFrame;
    [cell layoutIfNeeded];
    return cell;
}

2) Subclass UITableViewCell. Set preferredMaxLayoutWidth manually for your labels in layoutSubviews. Also you need manually layout contentView, because it doesn't layout automatically after cell frame change (I don't know why, but it is)

- (void)layoutSubviews {
    [super layoutSubviews];
    [self.contentView layoutIfNeeded];
    self.yourLongTextLabel.preferredMaxLayoutWidth = self.yourLongTextLabel.width;
}

回答5:

I have a similar problem, at the first load, the row height was not calculated but after some scrolling or go to another screen and i come back to this screen rows are calculated. At the first load my items are loaded from the internet and at the second load my items are loaded first from Core Data and reloaded from internet and i noticed that rows height are calculated at the reload from internet. So i noticed that when tableView.reloadData() is called during segue animation (same problem with push and present segue), row height was not calculated. So i hidden the tableview at the view initialization and put an activity loader to prevent an ugly effect to the user and i call tableView.reloadData after 300ms and now the problem is solved. I think it's a UIKit bug but this workaround make the trick.

I put theses lines (Swift 3.0) in my item load completion handler

DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(300), execute: {
        self.tableView.isHidden = false
        self.loader.stopAnimating()
        self.tableView.reloadData()
    })

This explain why for some people, put a reloadData in layoutSubviews solve the issue

回答6:

In my case the last line of the UILabel was truncated when the cell was displayed for the first time. It happened pretty randomly and the only way to size it correctly was to scroll the cell out of the view and to bring it back. I tried all the possible solutions displayed so far (layoutIfNeeded..reloadData) but nothing worked for me. The trick was to set "Autoshrink" to Minimuum Font Scale (0.5 for me). Give it a try

回答7:

I have tried most of the answers to this question and could not get any of them to work. The only functional solution I found was to add the following to my UITableViewController subclass:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    UIView.performWithoutAnimation {
        tableView.beginUpdates()
        tableView.endUpdates()
    }
}

The UIView.performWithoutAnimation call is required, otherwise you will see the normal table view animation as the view controller loads.

回答8:

Add a constraint for all content within a table view custom cell, then estimate table view row height and set row hight to automatic dimension with in a viewdid load :

    override func viewDidLoad() {
    super.viewDidLoad()

    tableView.estimatedRowHeight = 70
    tableView.rowHeight = UITableViewAutomaticDimension
}

To fix that initial loading issue apply layoutIfNeeded method with in a custom table view cell :

class CustomTableViewCell: UITableViewCell {

override func awakeFromNib() {
    super.awakeFromNib()
    self.layoutIfNeeded()
    // Initialization code
}
}

回答9:

Setting preferredMaxLayoutWidth helps in my case. I added

cell.detailLabel.preferredMaxLayoutWidth = cell.frame.width

in my code.

Also refer to Single line text takes two lines in UILabel and http://openradar.appspot.com/17799811.

回答10:

calling cell.layoutIfNeeded() inside cellForRowAt worked for me on ios 10 and ios 11, but not on ios 9.

to get this work on ios 9 also, I call cell.layoutSubviews() and it did the trick.

回答11:

For me none of these approaches worked, but I discovered that the label had an explicit Preferred Width set in Interface Builder. Removing that (unchecking "Explicit") and then using UITableViewAutomaticDimension worked as expected.

回答12:

I tried all of the solutions in this page but unchecking use size classes then checking it again solved my problem.

Edit: Unchecking size classes causes a lot of problems on storyboard so I tried another solution. I populated my table view in my view controller's viewDidLoad and viewWillAppear methods. This solved my problem.

回答13:

I have the issue with resizing label so I nee just to do
chatTextLabel.text = chatMessage.message chatTextLabel?.updateConstraints() after setting up the text

// full code

func setContent() {
    chatTextLabel.text = chatMessage.message
    chatTextLabel?.updateConstraints()

    let labelTextWidth = (chatTextLabel?.intrinsicContentSize().width) ?? 0
    let labelTextHeight = chatTextLabel?.intrinsicContentSize().height

    guard labelTextWidth < originWidth && labelTextHeight <= singleLineRowheight else {
      trailingConstraint?.constant = trailingConstant
      return
    }
    trailingConstraint?.constant = trailingConstant + (originWidth - labelTextWidth)

  }

回答14:

In my case, I was updating in other cycle. So tableViewCell height was updated after labelText was set. I deleted async block.

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
     let cell = tableView.dequeueReusableCell(withIdentifier:Identifier, for: indexPath) 
     // Check your cycle if update cycle is same or not
     // DispatchQueue.main.async {
        cell.label.text = nil
     // }
}

回答15:

Just make sure you're not setting the label text in 'willdisplaycell' delegate method of table view. Set the label text in 'cellForRowAtindexPath' delegate method for dynamic height calculation.

You're Welcome :)

回答16:

In my case, a stack view in the cell was causing the problem. It's a bug apparently. Once I removed it, the problem was solved.

回答17:

The problem is that the initial cells load before we have a valid row height. The workaround is to force a table reload when the view appears.

- (void)viewDidAppear:(BOOL)animated
{
  [super viewDidAppear:animated];
  [self.tableView reloadData];
}

回答18:

none of the above solutions worked for me, what worked is this recipe of a magic: call them in this order:

tableView.reloadData()
tableView.layoutIfNeeded() tableView.beginUpdates() tableView.endUpdates()

my tableView data are populated from a web service, in the call back of the connection I write the above lines.

回答19:

For iOS 12+ only, 2019 onwards...

An ongoing example of Apple's occasional bizarre incompetence, where problems go on for literally years.

It does seem to be the case that

        cell.layoutIfNeeded()
        return cell

will fix it. (You're losing some performance of course.)

Such is life with Apple.

回答20:

In my case, the issue with the cell height takes place after the initial table view is loaded, and a user action takes place (tapping on a button in a cell that has an effect of changing the cell height). I have been unable to get the cell to change its height unless I do:

[self.tableView reloadData];

I did try

[cell layoutIfNeeded];

but that didn't work.

回答21:

In Swift 3. I had to call self.layoutIfNeeded() each time I update the text of the reusable cell.

import UIKit
import SnapKit

class CommentTableViewCell: UITableViewCell {

    static let reuseIdentifier = "CommentTableViewCell"

    var comment: Comment! {
        didSet {
            textLbl.attributedText = comment.attributedTextToDisplay()
            self.layoutIfNeeded() //This is a fix to make propper automatic dimentions (height).
        }
    }

    internal var textLbl = UILabel()

    override func layoutSubviews() {
        super.layoutSubviews()

        if textLbl.superview == nil {
            textLbl.numberOfLines = 0
            textLbl.lineBreakMode = .byWordWrapping
            self.contentView.addSubview(textLbl)
            textLbl.snp.makeConstraints({ (make) in
                make.left.equalTo(contentView.snp.left).inset(10)
                make.right.equalTo(contentView.snp.right).inset(10)
                make.top.equalTo(contentView.snp.top).inset(10)
                make.bottom.equalTo(contentView.snp.bottom).inset(10)
            })
        }
    }
}

---

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let comment = comments[indexPath.row]
        let cell = tableView.dequeueReusableCell(withIdentifier: CommentTableViewCell.reuseIdentifier, for: indexPath) as! CommentTableViewCell
        cell.selectionStyle = .none
        cell.comment = comment
        return cell
    }

---

commentsTableView.rowHeight = UITableViewAutomaticDimension
    commentsTableView.estimatedRowHeight = 140

回答22:

None of the above solutions worked but the following combination of the suggestions did.

Had to add the following in viewDidLoad().

DispatchQueue.main.async {

        self.tableView.reloadData()

        self.tableView.setNeedsLayout()
        self.tableView.layoutIfNeeded()

        self.tableView.reloadData()

    }

The above combination of reloadData, setNeedsLayout and layoutIfNeeded worked but not any other. Could be specific to the cells in the project though. And yes, had to invoke reloadData twice to make it work.

Also set the following in viewDidLoad

tableView.rowHeight = UITableViewAutomaticDimension
tableView.estimatedRowHeight = MyEstimatedHeight

In tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath)

cell.setNeedsLayout()
cell.layoutIfNeeded() 

回答23:

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath{


//  call the method dynamiclabelHeightForText
}

use the above method which return the height for the row dynamically. And assign the same dynamic height to the the lable you are using.

-(int)dynamiclabelHeightForText:(NSString *)text :(int)width :(UIFont *)font
{

    CGSize maximumLabelSize = CGSizeMake(width,2500);

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


    return expectedLabelSize.height;


}

This code helps you finding the dynamic height for text displaying in the label.

回答24:

I ran into this issue and fixed it by moving my view/label initialization code FROM tableView(willDisplay cell:) TO tableView(cellForRowAt:).

来源：https://stackoverflow.com/questions/25971147/uitableview-dynamic-cell-heights-only-correct-after-some-scrolling