协议版本的clearlight的答案上面，因为协议是伟大的。随便放哪都行。扣篮!

extension UITextViewPlaceholder where Self: UIViewController {

    // Use this in ViewController's ViewDidLoad method.
    func addPlaceholder(text: String, toTextView: UITextView, font: UIFont? = nil) {
        placeholderLabel = UILabel()
        placeholderLabel.text = text
        placeholderLabel.font = font ?? UIFont.italicSystemFont(ofSize: (toTextView.font?.pointSize)!)
        placeholderLabel.sizeToFit()
        toTextView.addSubview(placeholderLabel)
        placeholderLabel.frame.origin = CGPoint(x: 5, y: (toTextView.font?.pointSize)! / 2)
        placeholderLabel.textColor = UIColor.lightGray
        placeholderLabel.isHidden = !toTextView.text.isEmpty
    }

    // Use this function in the ViewController's textViewDidChange delegate method.
    func textViewWithPlaceholderDidChange(_ textView: UITextView) {
        placeholderLabel.isHidden = !textView.text.isEmpty
    }
}

迅速的回答

这是一个自定义类，用于动画占位符。

class CustomTextView: UITextView {
    
    //   MARK: - public
    
    public var placeHolderText: String? = "Enter Reason.."
    
    public lazy var placeHolderLabel: UILabel! = {
        let placeHolderLabel = UILabel(frame: .zero)
        placeHolderLabel.numberOfLines = 0
        placeHolderLabel.backgroundColor = .clear
        placeHolderLabel.alpha = 0.5
        return placeHolderLabel
    }()
    
    //   MARK: - Init
    
    override init(frame: CGRect, textContainer: NSTextContainer?) {
        super.init(frame: frame, textContainer: textContainer)
        enableNotifications()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        enableNotifications()
    }
    
    func setup() {
        placeHolderLabel.frame = CGRect(x: 8, y: 8, width: self.bounds.size.width - 16, height: 15)
        placeHolderLabel.sizeToFit()
    }
    
    //   MARK: - Cycle
    
    override func awakeFromNib() {
        super.awakeFromNib()
        
        textContainerInset = UIEdgeInsets(top: 8, left: 5, bottom: 8, right: 8)
        returnKeyType = .done
        addSubview(placeHolderLabel)
        placeHolderLabel.frame = CGRect(x: 8, y: 8, width: self.bounds.size.width - 16, height: 15)
        placeHolderLabel.textColor = textColor
        placeHolderLabel.font = font
        placeHolderLabel.text = placeHolderText
        bringSubviewToFront(placeHolderLabel)
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        setup()
    }
    
    //   MARK: - Notifications
    
    private func enableNotifications() {
        NotificationCenter.default.addObserver(self, selector: #selector(textDidChangeNotification(_:)), name: UITextView.textDidChangeNotification , object: nil)
    }
    
    @objc func textDidChangeNotification(_ notify: Notification) {
        guard self == notify.object as? UITextView else { return }
        guard placeHolderText != nil else { return }
        
        UIView.animate(withDuration: 0.25, animations: {
            self.placeHolderLabel.alpha = (self.text.count == 0) ? 0.5 : 0
        }, completion: nil)
    }
    
}

我不知道为什么人们会把这个问题复杂化....这是相当直接和简单的。下面是UITextView的一个子类，它提供了所请求的功能。

- (void)customInit
{
    self.contentMode = UIViewContentModeRedraw;
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}

    - (void)textChanged:(NSNotification *)notification
    {
        if (notification.object == self) {
            if(self.textStorage.length != 0 || !self.textStorage.length) {
                [self setNeedsDisplay];
            }
        }
    }


    #pragma mark - Setters

    - (void)setPlaceholderText:(NSString *)placeholderText withFont:(UIFont *)font
    {
        self.placeholderText = placeholderText;
        self.placeholderTextFont = font;

    }



    - (void)drawRect:(CGRect)rect
    {
        [super drawRect:rect];
        [[UIColor lightGrayColor] setFill];

        if (self.textStorage.length != 0) {
            return;
        }

        CGRect inset = CGRectInset(rect, 8, 8);//Default rect insets for textView
        NSDictionary *attributes =  @{NSFontAttributeName: self.placeholderTextFont, NSForegroundColorAttributeName: [UIColor grayColor]};
        [self.placeholderText drawInRect:inset withAttributes:attributes];
    }`

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)

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。

对我来说，一个简单而快速的解决方法是:

@IBDesignable
class PlaceHolderTextView: UITextView {

    @IBInspectable var placeholder: String = "" {
         didSet{
             updatePlaceHolder()
        }
    }

    @IBInspectable var placeholderColor: UIColor = UIColor.gray {
        didSet {
            updatePlaceHolder()
        }
    }

    private var originalTextColor = UIColor.darkText
    private var originalText: String = ""

    private func updatePlaceHolder() {

        if self.text == "" || self.text == placeholder  {

            self.text = placeholder
            self.textColor = placeholderColor
            if let color = self.textColor {

                self.originalTextColor = color
            }
            self.originalText = ""
        } else {
            self.textColor = self.originalTextColor
            self.originalText = self.text
        }

    }

    override func becomeFirstResponder() -> Bool {
        let result = super.becomeFirstResponder()
        self.text = self.originalText
        self.textColor = self.originalTextColor
        return result
    }
    override func resignFirstResponder() -> Bool {
        let result = super.resignFirstResponder()
        updatePlaceHolder()

        return result
    }
}