另一个解决方案是使用keyboardWillHide和keyboardWillShow通知，就像我做的那样。

首先，您需要分别处理viewWillAppear和viewWillAppear方法中的侦听和取消侦听通知(以处理内存泄漏)。

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    setupKeyboardNotificationListeners(enable: true)
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    setupKeyboardNotificationListeners(enable: false)
}

然后是处理监听/取消监听通知的方法:

private func setupKeyboardNotificationListeners(enable: Bool) {
        if enable {
            NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
            NotificationCenter.default.addObserver(self, selector: #selector(self.keyboardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
        } else {
            NotificationCenter.default.removeObserver(self)
        }
    }

然后在keyboardWillHide和keyboardWillShow的两个方法中，你处理文本的占位符和颜色变化。

@objc func keyboardWillShow(notification: NSNotification) {
    if self.textView.text == self.placeholder {
        self.textView.text = ""
        self.textView.textColor = .black
    }
}

@objc func keyboardWillHide(notification: NSNotification) {
    if self.textView.text.isEmpty {
        self.textView.text = self.placeholder
        self.textView.textColor = .lightGrey
    }
}

我发现这个解决方案是目前为止最好的，因为文本会在键盘出现时立即删除，而不是在用户开始输入时删除，这可能会导致混乱。

我通过使用两个不同的文本视图来做到这一点:

一个在后台用作占位符。 一个在前台(具有透明背景)，用户实际输入。

其思想是，一旦用户开始在前景视图中输入内容，后台的占位符就会消失(如果用户删除了所有内容，则会重新出现)。因此，它的行为完全类似于单行文本字段的占位符。

这是我用的代码。注意，descriptionField是用户键入的字段，descriptionPlaceholder是后台的字段。

func textViewDidChange(descriptionField: UITextView) {
    if descriptionField.text.isEmpty == false {
        descriptionPlaceholder.text = ""
    } else {
        descriptionPlaceholder.text = descriptionPlaceholderText
    }
}

这是我准备使用的解决方案，如果您正在处理多个文本视图

func textViewShouldBeginEditing(textView: UITextView) -> Bool {        
    // Set cursor to the beginning if placeholder is set
    if textView.textColor == UIColor.lightGrayColor() {
        textView.selectedTextRange = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)
    }

    return true
}

func textView(textView: UITextView, shouldChangeTextInRange range: NSRange, replacementText text: String) -> Bool {
    // Remove placeholder
    if textView.textColor == UIColor.lightGrayColor() && text.characters.count > 0 {
        textView.text = ""
        textView.textColor = UIColor.blackColor()
    }

    if text == "\n" {
        textView.resignFirstResponder()
        return false
    }

    return true
}

func textViewDidChange(textView: UITextView) {
    // Set placeholder if text is empty
    if textView.text.isEmpty {
        textView.text = NSLocalizedString("Hint", comment: "hint")
        textView.textColor = UIColor.lightGrayColor()
        textView.selectedTextRange = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)
    }
}

func textViewDidChangeSelection(textView: UITextView) {
    // Set cursor to the beginning if placeholder is set
    let firstPosition = textView.textRangeFromPosition(textView.beginningOfDocument, toPosition: textView.beginningOfDocument)

    // Do not change position recursively
    if textView.textColor == UIColor.lightGrayColor() && textView.selectedTextRange != firstPosition {
        textView.selectedTextRange = firstPosition
    }
}

我试着用clearlight的答案来简化代码。

extension UITextView{

    func setPlaceholder() {

        let placeholderLabel = UILabel()
        placeholderLabel.text = "Enter some text..."
        placeholderLabel.font = UIFont.italicSystemFont(ofSize: (self.font?.pointSize)!)
        placeholderLabel.sizeToFit()
        placeholderLabel.tag = 222
        placeholderLabel.frame.origin = CGPoint(x: 5, y: (self.font?.pointSize)! / 2)
        placeholderLabel.textColor = UIColor.lightGray
        placeholderLabel.isHidden = !self.text.isEmpty

        self.addSubview(placeholderLabel)
    }

    func checkPlaceholder() {
        let placeholderLabel = self.viewWithTag(222) as! UILabel
        placeholderLabel.isHidden = !self.text.isEmpty
    }

}

使用

override func viewDidLoad() {
    textView.delegate = self
    textView.setPlaceholder()
}

func textViewDidChange(_ textView: UITextView) {
    textView.checkPlaceholder()
}

斯威夫特

这是一个Swiftui TextView使用UIVIewRepresentable，具有占位符功能和边界颜色

struct TextView: UIViewRepresentable {

@Binding var text: String
var placeholderText: String
var textStyle: UIFont.TextStyle

func makeUIView(context: Context) -> UITextView {
    let textView = UITextView()

    textView.font = UIFont.preferredFont(forTextStyle: textStyle)
    textView.autocapitalizationType = .sentences
    textView.isSelectable = true
    textView.isUserInteractionEnabled = true
    textView.delegate = context.coordinator
    textView.layer.borderWidth = 0.6
    textView.layer.borderColor = UIColor.lightGray.cgColor
    textView.layer.cornerRadius = 10
    textView.text = placeholderText
    textView.textColor = UIColor.lightGray
    return textView
}

func updateUIView(_ uiView: UITextView, context: Context) {
    uiView.text = text
    uiView.font = UIFont.preferredFont(forTextStyle: textStyle)
}

func makeCoordinator() -> Coordinator {
    Coordinator(self)
}
 
class Coordinator: NSObject, UITextViewDelegate {
    var parent: TextView
 
    init(_ parent: TextView) {
        self.parent = parent
    }
 
    func textViewDidChange(_ textView: UITextView) {
        self.parent.text = textView.text
    }
    
    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == UIColor.lightGray {
            textView.text = nil
            textView.textColor = UIColor.black
        }
    }
    
    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
            textView.text = self.parent.placeholderText
            textView.textColor = UIColor.lightGray
        }
    }
}

}

然后在你的视图中你可以这样使用它

TextView(text: self.$viewModel.addPostCommentText, placeholderText: "Share your story about this cash", textStyle: .body)
                .padding()
                .frame(height: 150)

基于这里已经给出的一些很好的建议，我能够将以下轻量级的、与接口生成器兼容的UITextView子类组合在一起，它是:

包括可配置的占位符文本，样式就像UITextField一样。 不需要任何额外的子视图或约束。 不需要来自ViewController的任何委托或其他行为。 不需要任何通知。 保持占位符文本与查看字段文本属性的任何外部类完全分离。

任何改进建议都是受欢迎的，特别是如果有任何方法通过编程来获取iOS的占位符颜色，而不是硬编码它。

斯威夫特v5:

import UIKit
@IBDesignable class TextViewWithPlaceholder: UITextView {
    
    override var text: String! { // Ensures that the placeholder text is never returned as the field's text
        get {
            if showingPlaceholder {
                return "" // When showing the placeholder, there's no real text to return
            } else { return super.text }
        }
        set { super.text = newValue }
    }
    @IBInspectable var placeholderText: String = ""
    @IBInspectable var placeholderTextColor: UIColor = UIColor(red: 0.78, green: 0.78, blue: 0.80, alpha: 1.0) // Standard iOS placeholder color (#C7C7CD). See https://stackoverflow.com/questions/31057746/whats-the-default-color-for-placeholder-text-in-uitextfield
    private var showingPlaceholder: Bool = true // Keeps track of whether the field is currently showing a placeholder
    
    override func didMoveToWindow() {
        super.didMoveToWindow()
        if text.isEmpty {
            showPlaceholderText() // Load up the placeholder text when first appearing, but not if coming back to a view where text was already entered
        }
    }
    
    override func becomeFirstResponder() -> Bool {
        // If the current text is the placeholder, remove it
        if showingPlaceholder {
            text = nil
            textColor = nil // Put the text back to the default, unmodified color
            showingPlaceholder = false
        }
        return super.becomeFirstResponder()
    }
    
    override func resignFirstResponder() -> Bool {
        // If there's no text, put the placeholder back
        if text.isEmpty {
            showPlaceholderText()
        }
        return super.resignFirstResponder()
    }
    
    private func showPlaceholderText() {
        showingPlaceholder = true
        textColor = placeholderTextColor
        text = placeholderText
    }
}