我通读了所有这些，但提出了一个非常简短的Swift 3解决方案，在我的所有测试中都有效。它可以更一般化一点，但过程很简单。这是整个东西，我称之为“TextViewWithPlaceholder”。

import UIKit

class TextViewWithPlaceholder: UITextView {

    public var placeholder: String?
    public var placeholderColor = UIColor.lightGray

    private var placeholderLabel: UILabel?

    // Set up notification listener when created from a XIB or storyboard.
    // You can also set up init() functions if you plan on creating
    // these programmatically.
    override func awakeFromNib() {
        super.awakeFromNib()

        NotificationCenter.default.addObserver(self,
                                           selector: #selector(TextViewWithPlaceholder.textDidChangeHandler(notification:)),
                                           name: .UITextViewTextDidChange,
                                           object: self)

        placeholderLabel = UILabel()
        placeholderLabel?.alpha = 0.85
        placeholderLabel?.textColor = placeholderColor
    }

    // By using layoutSubviews, you can size and position the placeholder
    // more accurately. I chose to hard-code the size of the placeholder
    // but you can combine this with other techniques shown in previous replies.
    override func layoutSubviews() {
        super.layoutSubviews()

        placeholderLabel?.textColor = placeholderColor
        placeholderLabel?.text = placeholder

        placeholderLabel?.frame = CGRect(x: 6, y: 4, width: self.bounds.size.width-16, height: 24)

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

    // Whenever the text changes, just trigger a new layout pass.
    func textDidChangeHandler(notification: Notification) {
        layoutSubviews()
    }
}

我能够做添加一个“占位符”到UITextView与很多少的代码。这就是我所做的:

UITextView *textView = [[UITextView alloc] initWithFrame:CGRectMake(60, 800, 200, 60)];
textView.text = @"Write characters here...";
textView.textColor=[UIColor grayColor];
textView.font = [UIFont fontWithName:@"Hevlatica" size:15];
textView.delegate=self;

我猜这不是一个真正的占位符，因为你必须在写之前删除文本，但如果你想要一些更简单的东西，它可能会有帮助。

模拟本机占位符

一个常见的抱怨是iOS没有为文本视图提供原生占位符功能。下面的UITextView扩展试图通过提供人们期望从本机特性获得的便利来解决这个问题，只需要一行代码就可以向textview实例添加占位符。

这个解决方案的缺点是，因为它菊花链委托调用，它很容易(不太可能)在iOS更新中更改UITextViewDelegate协议。具体来说，如果iOS添加了新的协议方法，并且你在带有占位符的文本视图的委托中实现了它们中的任何一个，这些方法将不会被调用，除非你也更新了扩展来转发这些调用。

或者，内联占位符的答案是一个坚如磐石的和简单的可以。

使用例子:

•如果获得占位符的文本视图没有使用UITextViewDelegate:

    /* Swift 3 */

    class NoteViewController : UIViewController {
        @IBOutlet weak var noteView: UITextView!
        override func viewDidLoad() {
            noteView.addPlaceholder("Enter some text...",  color: UIColor.lightGray)
        }
    }

                                            -- 或者——

•如果获得占位符的文本视图使用了UITextViewDelegate:

    /* Swift 3 */

    class NoteViewController : UIViewController, UITextViewDelegate {
        @IBOutlet weak var noteView: UITextView!
        override func viewDidLoad() {
            noteView.addPlaceholder("Phone #", color: UIColor.lightGray, delegate: self)
        }
    }

实现(UITextView扩展):

/* Swift 3 */

extension UITextView: UITextViewDelegate
{

    func addPlaceholder(_ placeholderText : String, 
                      color : UIColor? = UIColor.lightGray,
                      delegate : UITextViewDelegate? = nil) {

        self.delegate = self             // Make receiving textview instance a delegate
        let placeholder = UITextView()   // Need delegate storage ULabel doesn't provide
        placeholder.isUserInteractionEnabled = false  //... so we *simulate* UILabel
        self.addSubview(placeholder)     // Add to text view instance's view tree               
        placeholder.sizeToFit()          // Constrain to fit inside parent text view
        placeholder.tintColor = UIColor.clear // Unused in textviews. Can host our 'tag'
        placeholder.frame.origin = CGPoint(x: 5, y: 0) // Don't cover I-beam cursor
        placeholder.delegate = delegate  // Use as cache for caller's delegate 
        placeholder.font = UIFont.italicSystemFont(ofSize: (self.font?.pointSize)!)
        placeholder.text = placeholderText
        placeholder.textColor = color
    }

      
    func findPlaceholder() -> UITextView? { // find placeholder by its tag 
        for subview in self.subviews {
            if let textview = subview as? UITextView {
                if textview.tintColor == UIColor.clear { // sneaky tagging scheme
                    return textview
                }
            }
        }
        return nil
    }
     
    /* 
     * Safely daisychain to caller delegate methods as appropriate...
     */

    public func textViewDidChange(_ textView: UITextView) { // ←  need this delegate method
        if let placeholder = findPlaceholder() {
            placeholder.isHidden = !self.text.isEmpty // ← ... to do this
            placeholder.delegate?.textViewDidChange?(textView)
        } 
    }

    /* 
     * Since we're becoming a delegate on behalf of this placeholder-enabled
     * text view instance, we must forward *all* that protocol's activity expected
     * by the instance, not just the particular optional protocol method we need to
     * intercept, above.
     */

    public func textViewDidEndEditing(_ textView: UITextView) {
        if let placeholder = findPlaceholder() {
            placeholder.delegate?.textViewDidEndEditing?(textView)
        } 
    }

    public func textViewDidBeginEditing(_ textView: UITextView) {
        if let placeholder = findPlaceholder() {
            placeholder.delegate?.textViewDidBeginEditing?(textView)
        } 
    }

    public  func textViewDidChangeSelection(_ textView: UITextView) {
        if let placeholder = findPlaceholder() {
            placeholder.delegate?.textViewDidChangeSelection?(textView)
        } 
    }

    public func textViewShouldEndEditing(_ textView: UITextView) -> Bool {
        if let placeholder = findPlaceholder() {
            guard let retval = placeholder.delegate?.textViewShouldEndEditing?(textView) else {
                return true
            }
            return retval
        }
        return true
    }

    public func textViewShouldBeginEditing(_ textView: UITextView) -> Bool {
        if let placeholder = findPlaceholder() {
            guard let retval = placeholder.delegate?.textViewShouldBeginEditing?(textView) else {
                return true
            }
            return retval
        } 
        return true
    }

    public func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        if let placeholder = findPlaceholder() {
            guard let retval = placeholder.delegate?.textView?(textView, shouldChangeTextIn: range, replacementText: text) else {
                return true
            }
            return retval
        } 
        return true
    }

    public func textView(_ textView: UITextView, shouldInteractWith URL: URL, in characterRange: NSRange, interaction: UITextItemInteraction) -> Bool {
        if let placeholder = findPlaceholder() {
                guard let retval = placeholder.delegate?.textView?(textView, shouldInteractWith: URL, in: characterRange, interaction:
                    interaction) else {
                        return true
            }
            return retval
        }
        return true
    }

    public func textView(_ textView: UITextView, shouldInteractWith textAttachment: NSTextAttachment, in characterRange: NSRange, interaction: UITextItemInteraction) -> Bool {
        if let placeholder = findPlaceholder() {
            guard let retval = placeholder.delegate?.textView?(textView, shouldInteractWith: textAttachment, in: characterRange, interaction: interaction) else {
                return true
            }
            return retval
        }
        return true
    }
}

1. 作为一个像UITextView这样的基本iOS类的扩展，重要的是要知道这段代码没有与任何不激活占位符的textview交互，例如textview实例没有被调用addPlaceholder()初始化

2. 支持占位符的文本视图透明地变成一个UITextViewDelegate来跟踪字符计数，以控制占位符可见性。如果一个委托被传递给addPlaceholder()，这段代码会将委托回调给该委托。

3.作者正在研究如何检查UITextViewDelegate协议并自动代理它，而不必硬编码每个方法。这将使代码免受方法签名更改和添加到协议中的新方法的影响。

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。 保持该文本与查看字段的文本属性的任何外部类完全分离。

欢迎提出改进建议。

编辑1:更新为重置占位符格式，如果实际文本以编程方式设置。

编辑2:现在可以以编程方式检索占位符文本颜色。

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 {
            if showingPlaceholder {
                removePlaceholderFormatting() // If the placeholder text is what's being changed, it's no longer the placeholder
            }
            super.text = newValue
        }
    }
    @IBInspectable var placeholderText: String = ""
    @IBInspectable var placeholderTextColor: UIColor = .placeholderText
    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 public func becomeFirstResponder() -> Bool {
        
        // If the current text is the placeholder, remove it
        if showingPlaceholder {
            text = nil
            removePlaceholderFormatting()
        }
        return super.becomeFirstResponder()
    }
    
    override public func resignFirstResponder() -> Bool {
        
        // If there's no text, put the placeholder back
        if text.isEmpty {
            showPlaceholderText()
        }
        return super.resignFirstResponder()
    }
    
    private func showPlaceholderText() {
        
        text = placeholderText
        showingPlaceholder = true
        textColor = placeholderTextColor
    }
    
    private func removePlaceholderFormatting() {
        
        showingPlaceholder = false
        textColor = nil // Put the text back to the default, unmodified color
    }
}

TextView占位符

import UIKit

@IBDesignable
open class KMPlaceholderTextView: UITextView {

    private struct Constants {
        static let defaultiOSPlaceholderColor = UIColor(red: 0.0, green: 0.0, blue: 0.0980392, alpha: 0.22)
    }

    public let placeholderLabel: UILabel = UILabel()

    private var placeholderLabelConstraints = [NSLayoutConstraint]()

    @IBInspectable open var placeholder: String = "" {
        didSet {
            placeholderLabel.text = placeholder
        }
    }

    @IBInspectable open var placeholderColor: UIColor = KMPlaceholderTextView.Constants.defaultiOSPlaceholderColor {
        didSet {
            placeholderLabel.textColor = placeholderColor
        }
    }

    override open var font: UIFont! {
        didSet {
            if placeholderFont == nil {
                placeholderLabel.font = font
            }
        }
    }

    open var placeholderFont: UIFont? {
        didSet {
            let font = (placeholderFont != nil) ? placeholderFont : self.font
            placeholderLabel.font = font
        }
    }

    override open var textAlignment: NSTextAlignment {
        didSet {
            placeholderLabel.textAlignment = textAlignment
        }
    }

    override open var text: String! {
        didSet {
            textDidChange()
        }
    }

    override open var attributedText: NSAttributedString! {
        didSet {
            textDidChange()
        }
    }

    override open var textContainerInset: UIEdgeInsets {
        didSet {
            updateConstraintsForPlaceholderLabel()
        }
    }

    override public init(frame: CGRect, textContainer: NSTextContainer?) {
        super.init(frame: frame, textContainer: textContainer)
        commonInit()
    }

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

    private func commonInit() {
        #if swift(>=4.2)
        let notificationName = UITextView.textDidChangeNotification
        #else
        let notificationName = NSNotification.Name.UITextView.textDidChangeNotification
        #endif

        NotificationCenter.default.addObserver(self,
                                               selector: #selector(textDidChange),
                                               name: notificationName,
                                               object: nil)

        placeholderLabel.font = font
        placeholderLabel.textColor = placeholderColor
        placeholderLabel.textAlignment = textAlignment
        placeholderLabel.text = placeholder
        placeholderLabel.numberOfLines = 0
        placeholderLabel.backgroundColor = UIColor.clear
        placeholderLabel.translatesAutoresizingMaskIntoConstraints = false
        addSubview(placeholderLabel)
        updateConstraintsForPlaceholderLabel()
    }

    private func updateConstraintsForPlaceholderLabel() {
        var newConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:|-(\(textContainerInset.left + textContainer.lineFragmentPadding))-[placeholder]",
            options: [],
            metrics: nil,
            views: ["placeholder": placeholderLabel])
        newConstraints += NSLayoutConstraint.constraints(withVisualFormat: "V:|-(\(textContainerInset.top))-[placeholder]",
            options: [],
            metrics: nil,
            views: ["placeholder": placeholderLabel])
        newConstraints.append(NSLayoutConstraint(
            item: placeholderLabel,
            attribute: .width,
            relatedBy: .equal,
            toItem: self,
            attribute: .width,
            multiplier: 1.0,
            constant: -(textContainerInset.left + textContainerInset.right + textContainer.lineFragmentPadding * 2.0)
        ))
        removeConstraints(placeholderLabelConstraints)
        addConstraints(newConstraints)
        placeholderLabelConstraints = newConstraints
    }

    @objc private func textDidChange() {
        placeholderLabel.isHidden = !text.isEmpty
        self.layoutIfNeeded()
    }

    open override func layoutSubviews() {
        super.layoutSubviews()
        placeholderLabel.preferredMaxLayoutWidth = textContainer.size.width - textContainer.lineFragmentPadding * 2.0
    }

    deinit {
        #if swift(>=4.2)
        let notificationName = UITextView.textDidChangeNotification
        #else
        let notificationName = NSNotification.Name.UITextView.textDidChangeNotification
        #endif

        NotificationCenter.default.removeObserver(self,
                                                  name: notificationName,
                                                  object: nil)
    }

}

使用

另一个答案是:

https://github.com/gcamp/GCPlaceholderTextView

改变类UITextView在IB到GCPlaceholderTextView 并设置占位符属性