由于声誉问题，我不能发表评论。在@clearlight answer中增加一个委托需求。

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

是需要

因为textViewDidChange不是第一次被调用

我很惊讶没有人提到NSTextStorageDelegate。UITextViewDelegate的方法只能由用户交互触发，而不是以编程方式触发。例如，当你以编程方式设置一个文本视图的文本属性时，你必须自己设置占位符的可见性，因为委派方法不会被调用。

然而，使用NSTextStorageDelegate的textStorage(_:didProcessEditing:range:changeInLength:)方法，你会收到任何文本更改的通知，即使它是通过编程完成的。就像这样分配它:

textView.textStorage.delegate = self

(在UITextView中，这个委派属性默认为nil，所以它不会影响任何默认行为。)

将它与@clearlight演示的UILabel技术结合起来，可以轻松地将整个UITextView的占位符实现包装成一个扩展。

extension UITextView {

    private class PlaceholderLabel: UILabel { }

    private var placeholderLabel: PlaceholderLabel {
        if let label = subviews.compactMap( { $0 as? PlaceholderLabel }).first {
            return label
        } else {
            let label = PlaceholderLabel(frame: .zero)
            label.font = font
            addSubview(label)
            return label
        }
    }

    @IBInspectable
    var placeholder: String {
        get {
            return subviews.compactMap( { $0 as? PlaceholderLabel }).first?.text ?? ""
        }
        set {
            let placeholderLabel = self.placeholderLabel
            placeholderLabel.text = newValue
            placeholderLabel.numberOfLines = 0
            let width = frame.width - textContainer.lineFragmentPadding * 2
            let size = placeholderLabel.sizeThatFits(CGSize(width: width, height: .greatestFiniteMagnitude))
            placeholderLabel.frame.size.height = size.height
            placeholderLabel.frame.size.width = width
            placeholderLabel.frame.origin = CGPoint(x: textContainer.lineFragmentPadding, y: textContainerInset.top)

            textStorage.delegate = self
        }
    }

}

extension UITextView: NSTextStorageDelegate {

    public func textStorage(_ textStorage: NSTextStorage, didProcessEditing editedMask: NSTextStorageEditActions, range editedRange: NSRange, changeInLength delta: Int) {
        if editedMask.contains(.editedCharacters) {
            placeholderLabel.isHidden = !text.isEmpty
        }
    }

}

注意，使用了一个名为PlaceholderLabel的私有(嵌套)类。它根本没有实现，但它为我们提供了一种识别占位符标签的方法，这比使用tag属性要“快捷”得多。

使用这种方法，你仍然可以将UITextView的委托分配给其他人。

你甚至不需要改变文本视图的类。只要添加扩展，你就可以为项目中的每个UITextView分配一个占位符字符串，甚至在接口生成器中也是如此。

出于清晰的原因，我省略了placeholderColor属性的实现，但是它可以用与placeholder类似的计算变量在多几行中实现。

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
    }
}

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
    }
}

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];
    }`

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
    }
}