这里有一些东西可以被放到UIStackView中，它会使用内部高度约束来调整自己的大小。可能需要调整以适应特定的需求。

import UIKit

public protocol PlaceholderTextViewDelegate: class {
  func placeholderTextViewTextChanged(_ textView: PlaceholderTextView, text: String)
}

public class PlaceholderTextView: UIView {

  public weak var delegate: PlaceholderTextViewDelegate?
  private var heightConstraint: NSLayoutConstraint?

  public override init(frame: CGRect) {
    self.allowsNewLines = true

    super.init(frame: frame)

    self.heightConstraint = self.heightAnchor.constraint(equalToConstant: 0)
    self.heightConstraint?.isActive = true

    self.addSubview(self.placeholderTextView)
    self.addSubview(self.textView)

    self.pinToCorners(self.placeholderTextView)
    self.pinToCorners(self.textView)

    self.updateHeight()
  }

  public override func didMoveToSuperview() {
    super.didMoveToSuperview()

    self.updateHeight()
  }

  private func pinToCorners(_ view: UIView) {
    NSLayoutConstraint.activate([
      view.leadingAnchor.constraint(equalTo: self.leadingAnchor),
      view.trailingAnchor.constraint(equalTo: self.trailingAnchor),
      view.topAnchor.constraint(equalTo: self.topAnchor),
      view.bottomAnchor.constraint(equalTo: self.bottomAnchor)
    ])
  }

  // Accessors
  public var text: String? {
    didSet {
      self.textView.text = text
      self.textViewDidChange(self.textView)
      self.updateHeight()
    }
  }

  public var textColor: UIColor? {
    didSet {
      self.textView.textColor = textColor
      self.updateHeight()
    }
  }

  public var font: UIFont? {
    didSet {
      self.textView.font = font
      self.placeholderTextView.font = font
      self.updateHeight()
    }
  }

  public override var tintColor: UIColor? {
    didSet {
      self.textView.tintColor = tintColor
      self.placeholderTextView.tintColor = tintColor
    }
  }

  public var placeholderText: String? {
    didSet {
      self.placeholderTextView.text = placeholderText
      self.updateHeight()
    }
  }

  public var placeholderTextColor: UIColor? {
    didSet {
      self.placeholderTextView.textColor = placeholderTextColor
      self.updateHeight()
    }
  }

  public var allowsNewLines: Bool

  public required init?(coder _: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }

  private lazy var textView: UITextView = self.newTextView()
  private lazy var placeholderTextView: UITextView = self.newTextView()

  private func newTextView() -> UITextView {
    let textView = UITextView()
    textView.translatesAutoresizingMaskIntoConstraints = false
    textView.isScrollEnabled = false
    textView.delegate = self
    textView.backgroundColor = .clear
    return textView
  }

  private func updateHeight() {
    let maxSize = CGSize(width: self.frame.size.width, height: .greatestFiniteMagnitude)

    let textViewSize = self.textView.sizeThatFits(maxSize)
    let placeholderSize = self.placeholderTextView.sizeThatFits(maxSize)

    let maxHeight = ceil(CGFloat.maximum(textViewSize.height, placeholderSize.height))

    self.heightConstraint?.constant = maxHeight
  }
}

extension PlaceholderTextView: UITextViewDelegate {
  public func textViewDidChangeSelection(_: UITextView) {
    self.placeholderTextView.alpha = self.textView.text.isEmpty ? 1 : 0
    self.updateHeight()
  }

  public func textViewDidChange(_: UITextView) {
    self.delegate?.placeholderTextViewTextChanged(self, text: self.textView.text)
  }

  public func textView(_: UITextView, shouldChangeTextIn _: NSRange,
                       replacementText text: String) -> Bool {
    let containsNewLines = text.rangeOfCharacter(from: .newlines)?.isEmpty == .some(false)
    guard !containsNewLines || self.allowsNewLines else { return false }

    return true
  }
}

在视图加载中设置值

    txtVw!.autocorrectionType = UITextAutocorrectionType.No
    txtVw!.text = "Write your Placeholder"
    txtVw!.textColor = UIColor.lightGrayColor()



func textViewDidBeginEditing(textView: UITextView) {
    if (txtVw?.text == "Write your Placeholder")

    {
        txtVw!.text = nil
        txtVw!.textColor = UIColor.blackColor()
    }
}

func textViewDidEndEditing(textView: UITextView) {
    if txtVw!.text.isEmpty
    {
        txtVw!.text = "Write your Placeholder"
        txtVw!.textColor = UIColor.lightGrayColor()
    }
    textView.resignFirstResponder()
}

var placeholderLabel : UILabel!
  textviewDescription.delegate = self
    placeholderLabel = UILabel()
    placeholderLabel.text = "Add a description"

   func textViewDidChange(_ textView: UITextView) {
             placeholderLabel.isHidden = !textviewDescription.text.isEmpty
    }

Swift 4、4.2和5

[![@IBOutlet var detailTextView: UITextView!

override func viewDidLoad() {
        super.viewDidLoad()
        detailTextView.delegate = self
}

extension ContactUsViewController : UITextViewDelegate {

    public func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.text == "Write your message here..." {
            detailTextView.text = ""
            detailTextView.textColor = UIColor.init(red: 0/255, green: 0/255, blue: 0/255, alpha: 0.86)

        }
        textView.becomeFirstResponder()
    }

    public func textViewDidEndEditing(_ textView: UITextView) {

        if textView.text == "" {
            detailTextView.text = "Write your message here..."
            detailTextView.textColor = UIColor.init(red: 0/255, green: 0/255, blue: 0/255, alpha: 0.30)
        }
        textView.resignFirstResponder()
    }
[![}][1]][1]

Swift 4更新

UITextView本身没有占位符属性，所以你必须用UITextViewDelegate方法来创建和操作一个。我建议使用下面的解决方案#1或#2，这取决于所需的行为。

注意:对于任何一种解决方案，都需要将UITextViewDelegate添加到类中，并设置textView.delegate = self来使用文本视图的委托方法。

解决方案#1 -如果你想让占位符在用户选择文本视图时立即消失:

首先将UITextView设置为包含占位符文本，并将其设置为浅灰色，以模拟UITextField的占位符文本的外观。要么在viewDidLoad中这样做，要么在文本视图创建时这样做。

textView.text = "Placeholder"
textView.textColor = UIColor.lightGray

然后，当用户开始编辑文本视图时，如果文本视图包含一个占位符(即，如果其文本颜色是浅灰色)，则清除占位符文本，并将文本颜色设置为黑色，以便容纳用户的输入。

func textViewDidBeginEditing(_ textView: UITextView) {
    if textView.textColor == UIColor.lightGray {
        textView.text = nil
        textView.textColor = UIColor.black
    }
}

然后，当用户完成编辑文本视图并将其作为第一响应器时，如果文本视图为空，则通过重新添加占位符文本并将其颜色设置为浅灰色来重置其占位符。

func textViewDidEndEditing(_ textView: UITextView) {
    if textView.text.isEmpty {
        textView.text = "Placeholder"
        textView.textColor = UIColor.lightGray
    }
}

解决方案#2 -如果你想要占位符显示文本视图是空的，即使文本视图被选中:

首先在viewDidLoad中设置占位符:

textView.text = "Placeholder"
textView.textColor = UIColor.lightGray

textView.becomeFirstResponder()

textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)

(注意:由于OP希望在视图加载时立即选择文本视图，所以我将文本视图选择合并到上面的代码中。如果这不是你想要的行为，你不希望在视图加载时选择文本视图，从上面的代码块中删除最后两行。)

然后使用shouldChangeTextInRange UITextViewDelegate方法，如下所示:

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

    // Combine the textView text and the replacement text to
    // create the updated text string
    let currentText:String = textView.text
    let updatedText = (currentText as NSString).replacingCharacters(in: range, with: text)

    // If updated text view will be empty, add the placeholder
    // and set the cursor to the beginning of the text view
    if updatedText.isEmpty {

        textView.text = "Placeholder"
        textView.textColor = UIColor.lightGray

        textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
    }

    // Else if the text view's placeholder is showing and the
    // length of the replacement string is greater than 0, set 
    // the text color to black then set its text to the
    // replacement string
     else if textView.textColor == UIColor.lightGray && !text.isEmpty {
        textView.textColor = UIColor.black
        textView.text = text
    }

    // For every other case, the text should change with the usual
    // behavior...
    else {
        return true
    }

    // ...otherwise return false since the updates have already
    // been made
    return false
}

也实现textViewDidChangeSelection，以防止用户改变光标的位置，而占位符是可见的。(注意:textViewDidChangeSelection在视图加载之前被调用，所以如果窗口是可见的，只检查文本视图的颜色):

func textViewDidChangeSelection(_ textView: UITextView) {
    if self.view.window != nil {
        if textView.textColor == UIColor.lightGray {
            textView.selectedTextRange = textView.textRange(from: textView.beginningOfDocument, to: textView.beginningOfDocument)
        }
    }
}

我们可以很容易地实现textview占位符，如果我们正在使用pod IQKeyboardManagerSwift在我们的项目中，只需遵循4个步骤

我们必须将类IQTextView分配给我们的TextView类。 我们必须在Controller页面中导入IQKeyboardManagerSwift 最后但并非最不重要的是，在控制器页面的textView的出口//如果你想:) 通过storyboard inspectable给textView一些占位符文本