如何创建高度由其标签高度确定的 UITableView 标头？

Question

我想在我的 tableView 中添加一个标题。此标头包含 1 个 UILabel。标题高度应根据标签的行数计算。

在我的代码中，我使用标签 标头的所有边缘添加约束。这是我的尝试：

    //Add header to tableView
    header = UIView()
    header.backgroundColor = UIColor.yellowColor()
    tableView!.tableHeaderView = header

    //Create Label and add it to the header
    postBody = UILabel()
    postBody.text = "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog."
    postBody.font = UIFont(name: "Lato-Regular", size: 16.0)
    postBody.numberOfLines = 0
    postBody.backgroundColor = FlatLime()
    header.addSubview(postBody)

    //Enable constraints for each item
    postBody.translatesAutoresizingMaskIntoConstraints = false
    header.translatesAutoresizingMaskIntoConstraints = false

    //Add constraints to the header and post body
    let postBodyLeadingConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Leading, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Leading, multiplier: 1, constant: 0)
    postBodyLeadingConstraint.active = true

    let postBodyTrailingConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Trailing, multiplier: 1, constant: 0)
    postBodyTrailingConstraint.active = true


    let postBodyTopConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Top, multiplier: 1, constant: 0)
    postBodyTopConstraint.active = true


    let postBodyBottomConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Bottom, multiplier: 1, constant: 0)
    postBodyBottomConstraint.active = true


    //Calculate header size
    let size = header.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize)
    var frame = header.frame
    frame.size.height = size.height
    header.frame = frame
    tableView!.tableHeaderView = header
    header.layoutIfNeeded()

这是我的桌子：

    let nib = UINib(nibName: "MessagesTableViewCell", bundle: nil)
    let nibSimple = UINib(nibName: "SimpleMessagesTableViewCell", bundle: nil)
    self.tableView!.registerNib(nib, forCellReuseIdentifier: "MessagesTableViewCell")
    self.tableView!.registerNib(nibSimple, forCellReuseIdentifier: "SimpleMessagesTableViewCell")
    self.tableView!.dataSource = self
    self.tableView!.delegate = self
    self.tableView!.rowHeight = UITableViewAutomaticDimension
    self.tableView!.estimatedRowHeight = 100.0
    self.tableView!.separatorStyle = UITableViewCellSeparatorStyle.None
    self.tableView!.separatorColor = UIColor(hex: 0xf5f5f5)
    self.tableView!.separatorInset = UIEdgeInsetsMake(0, 0, 0, 0)
    self.tableView!.clipsToBounds = true
    self.tableView!.allowsSelection = false
    self.tableView!.allowsMultipleSelection = false
    self.tableView!.keyboardDismissMode = .OnDrag

如你所见，表头没有考虑标签的高度（我做了numberOfLines = 0）

Answer 1

UILabels 利用UIView 的intrinsicContentSize() 告诉自动布局它们应该是什么大小。然而，对于多行标签，内在内容大小是不明确的；这张桌子不知道它应该是又短又宽、又高又窄，还是介于两者之间。

为了解决这个问题，UILabel 有一个名为 preferredMaxLayoutWidth 的属性。设置此项会告诉多行标签它最多应该这么宽，并允许intrinsicContentSize() 找出并返回一个合适的高度来匹配。通过在您的示例中不设置 preferredMaxLayoutWidth，标签使其宽度不受限制，因此会计算单行长文本的高度。

preferredMaxLayoutWidth 的唯一复杂之处在于，在自动布局为您计算出宽度之前，您通常不知道标签的宽度。因此，在视图控制器子类（看起来您的代码示例可能来自）中设置它的位置位于viewDidLayoutSubviews：

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    postBody.preferredMaxLayoutWidth = CGRectGetWidth(postBody.frame)
    // then update the table header view
    if let header = tableView?.tableHeaderView {
        header.frame.size.height = header.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize).height
        tableView?.tableHeaderView = header
    }
}

显然，您需要为postBody 标签添加一个属性才能使其正常工作。

如果您不在 UIViewController 子类中，请告诉我，我将编辑我的答案。

Answer 2

使用情节提要实现

1. 在UItableView添加UITableViewCell新UIView并把他放在UILabel 通过自动布局连接它们
2. 在UILabel 中将行数设为0。
3. 在ViewDidLoad你的UILabel调用一个方法sizeToFit() 并指定UIView 的大小，这将是您的HeaderVew headerView.frame.size.height = headerLabel.frame.size.height

代码

    @IBOutlet weak var tableView: UITableView!
    @IBOutlet weak var headerView: UIView!
    @IBOutlet weak var headerLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        headerLabel.text = "tableViewdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarningdidReceiveMemoryWarning"
        headerLabel.sizeToFit()
        headerView.frame.size.height = headerLabel.frame.size.height
    }

截图

测试项目

test project link

Answer 3

我们遇到的第一个问题是header无法通过autolayout调整大小，详情见Is it possible to use AutoLayout with UITableView's tableHeaderView?

因此，我们必须手动计算表头的高度，例如：

@IBOutlet var table: UITableView!

var header: UIView?
var postBody: UILabel?

override func viewDidLoad() {
    super.viewDidLoad()

    let header = UIView()
    // don't forget to set this
    header.translatesAutoresizingMaskIntoConstraints = true
    header.backgroundColor = UIColor.yellowColor()

    let postBody = UILabel()
    postBody.translatesAutoresizingMaskIntoConstraints = false
    postBody.text = "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog."
    postBody.font = UIFont.systemFontOfSize(16.0)

    // don't forget to set this
    postBody.lineBreakMode = .ByWordWrapping
    postBody.numberOfLines = 0

    header.addSubview(postBody)

    let leadingConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Leading, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Leading, multiplier: 1, constant: 0)
    let trailingConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Trailing, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Trailing, multiplier: 1, constant: 0)
    let topConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Top, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Top, multiplier: 1, constant: 0)
    let bottomConstraint = NSLayoutConstraint(item: postBody, attribute: NSLayoutAttribute.Bottom, relatedBy: NSLayoutRelation.Equal, toItem: header, attribute: NSLayoutAttribute.Bottom, multiplier: 1, constant: 0)

    header.addConstraints([leadingConstraint, trailingConstraint, topConstraint, bottomConstraint])

    self.table.tableHeaderView = header

    self.header = header
    self.postBody = postBody
}

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    let text = postBody!.attributedText!

    let height = text.boundingRectWithSize(
        CGSizeMake(table.bounds.size.width, CGFloat.max),
        options: [.UsesLineFragmentOrigin],
        context: nil
    ).height

    header!.frame.size.height = height
}

您可能还想使用stefandouganhyde's answer 中的代码。如何计算高度并不重要。关键是tableHeaderView 的自动布局不会自动工作。

结果：

Answer 4

我们使用 NSLayoutManager 根据文本快速估计需要调整大小的项目的高度。这是基本思想：

override class func estimatedHeightForItem(text: String, atWidth width: CGFloat) -> CGFloat {

    let storage = NSTextStorage(string: text!)
    let container = NSTextContainer(size: CGSize(width: width, height: CGFloat.max))
    let layoutManager = NSLayoutManager()
    layoutManager.addTextContainer(container)
    storage.addLayoutManager(layoutManager)
    storage.addAttribute(NSFontAttributeName, value: UIFont.Body, range: NSRange(location: 0, length: storage.length))
    container.lineFragmentPadding = 0.0

    return layoutManager.usedRectForTextContainer(container).size.height 
}

Beslan's answer 可能更适合您的用例，但我发现更好地控制布局的处理方式。

Answer 5

//可能对你有帮助。

header = UIView(frame: CGRectMake(tableview.frame.origin.x,tableview.frame.origin.y, tableview.frame.size.width, 40))
header.backgroundColor = UIColor.yellowColor()

//Create Label and add it to the header
postBody = UILabel(frame: header.frame)
postBody.text = "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog."
postBody.font = UIFont(name: "Lato-Regular", size: 16.0)
postBody.numberOfLines = 0
postBody.backgroundColor = FlatLime()
header.addSubview(postBody)

let maximumLabelSize: CGSize = CGSizeMake(postBody.size.width, CGFloat.max);

let options: NSStringDrawingOptions  = NSStringDrawingOptions.UsesLineFragmentOrigin
let context: NSStringDrawingContext = NSStringDrawingContext()
        context.minimumScaleFactor = 0.8
        let attr: Dictionary = [NSFontAttributeName: postBody.font!]
        var size: CGSize? = postBody.text?.boundingRectWithSize(maximumLabelSize, options:options, attributes: attr, context: context).size

let frame = header.frame
frame.size.height = size?.height
header.frame = frame
postBody.frame = frame
tableView!.tableHeaderView = header

Answer 6

你可以通过使用它的字符串来计算标签的高度

let labelWidth = label.frame.width
let maxLabelSize = CGSize(width: labelWidth, height: CGFloat.max)
let actualLabelSize = label.text!.boundingRectWithSize(maxLabelSize, options: [.UsesLineFragmentOrigin], attributes: [NSFontAttributeName: label.font], context: nil)
let labelHeight = actualLabelSize.height