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)
        }
    }
}

迅速:

添加你的TextView @IBOutlet:

@IBOutlet weak var txtViewMessage: UITextView!

在viewWillAppear方法中，添加以下内容:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    txtViewMessage.delegate = self    // Give TextViewMessage delegate Method
    
    txtViewMessage.text = "Place Holder Name"
    txtViewMessage.textColor = UIColor.lightGray
}

请添加委托使用扩展(UITextViewDelegate):

// MARK: - UITextViewDelegate
extension ViewController: UITextViewDelegate {

    func textViewDidBeginEditing(_ textView: UITextView) {

        if !txtViewMessage.text!.isEmpty && txtViewMessage.text! == "Place Holder Name" {
            txtViewMessage.text = ""
            txtViewMessage.textColor = UIColor.black
        }
    }

    func textViewDidEndEditing(_ textView: UITextView) {
    
        if txtViewMessage.text.isEmpty {
            txtViewMessage.text = "Place Holder Name"
            txtViewMessage.textColor = UIColor.lightGray
        }
    }
}

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
    }
}

还有一个解决方案(Swift 3):

import UIKit

protocol PlaceholderTextViewDelegate {
    func placeholderTextViewDidChangeText(_ text:String)
    func placeholderTextViewDidEndEditing(_ text:String)
}

final class PlaceholderTextView: UITextView {

    var notifier:PlaceholderTextViewDelegate?

    var placeholder: String? {
        didSet {
            placeholderLabel?.text = placeholder
        }
    }
    var placeholderColor = UIColor.lightGray
    var placeholderFont = UIFont.appMainFontForSize(14.0) {
        didSet {
            placeholderLabel?.font = placeholderFont
        }
    }

    fileprivate var placeholderLabel: UILabel?

    // MARK: - LifeCycle

    init() {
        super.init(frame: CGRect.zero, textContainer: nil)
        awakeFromNib()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override func awakeFromNib() {
        super.awakeFromNib()

        self.delegate = self
        NotificationCenter.default.addObserver(self, selector: #selector(PlaceholderTextView.textDidChangeHandler(notification:)), name: .UITextViewTextDidChange, object: nil)

        placeholderLabel = UILabel()
        placeholderLabel?.textColor = placeholderColor
        placeholderLabel?.text = placeholder
        placeholderLabel?.textAlignment = .left
        placeholderLabel?.numberOfLines = 0
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        placeholderLabel?.font = placeholderFont

        var height:CGFloat = placeholderFont.lineHeight
        if let data = placeholderLabel?.text {

            let expectedDefaultWidth:CGFloat = bounds.size.width
            let fontSize:CGFloat = placeholderFont.pointSize

            let textView = UITextView()
            textView.text = data
            textView.font = UIFont.appMainFontForSize(fontSize)
            let sizeForTextView = textView.sizeThatFits(CGSize(width: expectedDefaultWidth,
                                                               height: CGFloat.greatestFiniteMagnitude))
            let expectedTextViewHeight = sizeForTextView.height

            if expectedTextViewHeight > height {
                height = expectedTextViewHeight
            }
        }

        placeholderLabel?.frame = CGRect(x: 5, y: 0, width: bounds.size.width - 16, height: height)

        if text.isEmpty {
            addSubview(placeholderLabel!)
            bringSubview(toFront: placeholderLabel!)
        } else {
            placeholderLabel?.removeFromSuperview()
        }
    }

    func textDidChangeHandler(notification: Notification) {
        layoutSubviews()
    }

}

extension PlaceholderTextView : UITextViewDelegate {
    // MARK: - UITextViewDelegate
    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        if(text == "\n") {
            textView.resignFirstResponder()
            return false
        }
        return true
    }

    func textViewDidChange(_ textView: UITextView) {
        notifier?.placeholderTextViewDidChangeText(textView.text)
    }

    func textViewDidEndEditing(_ textView: UITextView) {
        notifier?.placeholderTextViewDidEndEditing(textView.text)
    }
}

结果

文本视图委托方法

使用这两个委托方法，并在类中编写UITextViewDelegate

func textViewDidBeginEditing(_ textView: UITextView) {
    if (commentsTextView.text == "Type Your Comments")
    {
        commentsTextView.text = nil
        commentsTextView.textColor = UIColor.darkGray
    }
}

func textViewDidEndEditing(_ textView: UITextView) {
    if commentsTextView.text.isEmpty
    {
        commentsTextView.text = "Type Your Comments"
        commentsTextView.textColor = UIColor.darkGray
    }
    textView.resignFirstResponder()
}

斯威夫特5.2

独立的类

如果你想要一个类，你可以在任何地方使用，因为它是自包含的

import UIKit
class PlaceHolderTextView:UITextView, UITextViewDelegate{
var placeholderText = "placeholderText"

override func willMove(toSuperview newSuperview: UIView?) {
    textColor = .lightText
    delegate = self
}

func textViewDidBeginEditing(_ textView: UITextView) {
    if textView.text == placeholderText{
        placeholderText = textView.text
        textView.text = ""
        textView.textColor = .darkText
    }
}

func textViewDidEndEditing(_ textView: UITextView) {
    if textView.text == ""{
        textView.text = placeholderText
        textColor = .lightText
    }
}    
}

这里的关键是willMove(toSuperView:)函数，因为它允许你在添加到另一个视图的层次结构之前设置视图(类似于ViewControllers中的viewDidLoad/viewWillAppear)