下面是“SAMTextView”ObjC代码的Swift端口，作为对这个问题的第一批回答之一。我在iOS 8上进行了测试。我调整了一些东西，包括占位符文本的位置的边界偏移，因为原来的位置太高，太右了(在那个帖子的一个评论中使用了建议)。

我知道有很多简单的解决方案，但我喜欢子类化UITextView的方法，因为它是可重用的，而且我不必在使用它的机制时使类变得混乱。

斯威夫特2.2:

import UIKit

class PlaceholderTextView: UITextView {

    @IBInspectable var placeholderColor: UIColor = UIColor.lightGrayColor()
    @IBInspectable var placeholderText: String = ""

    override var font: UIFont? {
        didSet {
            setNeedsDisplay()
        }
    }

    override var contentInset: UIEdgeInsets {
        didSet {
            setNeedsDisplay()
        }
    }

    override var textAlignment: NSTextAlignment {
        didSet {
            setNeedsDisplay()
        }
    }

    override var text: String? {
        didSet {
            setNeedsDisplay()
        }
    }

    override var attributedText: NSAttributedString? {
        didSet {
            setNeedsDisplay()
        }
    }

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

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

    private func setUp() {
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(PlaceholderTextView.textChanged(_:)),
                                                         name: UITextViewTextDidChangeNotification, object: self)
    }

    func textChanged(notification: NSNotification) {
        setNeedsDisplay()
    }

    func placeholderRectForBounds(bounds: CGRect) -> CGRect {
        var x = contentInset.left + 4.0
        var y = contentInset.top  + 9.0
        let w = frame.size.width - contentInset.left - contentInset.right - 16.0
        let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0

        if let style = self.typingAttributes[NSParagraphStyleAttributeName] as? NSParagraphStyle {
            x += style.headIndent
            y += style.firstLineHeadIndent
        }
        return CGRect(x: x, y: y, width: w, height: h)
    }

    override func drawRect(rect: CGRect) {
        if text!.isEmpty && !placeholderText.isEmpty {
            let paragraphStyle = NSMutableParagraphStyle()
            paragraphStyle.alignment = textAlignment
            let attributes: [ String: AnyObject ] = [
                NSFontAttributeName : font!,
                NSForegroundColorAttributeName : placeholderColor,
                NSParagraphStyleAttributeName  : paragraphStyle]

            placeholderText.drawInRect(placeholderRectForBounds(bounds), withAttributes: attributes)
        }
        super.drawRect(rect)
    }
}

斯威夫特4.2:

import UIKit

class PlaceholderTextView: UITextView {

    @IBInspectable var placeholderColor: UIColor = UIColor.lightGray
    @IBInspectable var placeholderText: String = ""

    override var font: UIFont? {
        didSet {
            setNeedsDisplay()
        }
    }

    override var contentInset: UIEdgeInsets {
        didSet {
            setNeedsDisplay()
        }
    }

    override var textAlignment: NSTextAlignment {
        didSet {
            setNeedsDisplay()
        }
    }

    override var text: String? {
        didSet {
            setNeedsDisplay()
        }
    }

    override var attributedText: NSAttributedString? {
        didSet {
            setNeedsDisplay()
        }
    }

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

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

    private func setUp() {
        NotificationCenter.default.addObserver(self,
         selector: #selector(self.textChanged(notification:)),
         name: Notification.Name("UITextViewTextDidChangeNotification"),
         object: nil)
    }

    @objc func textChanged(notification: NSNotification) {
        setNeedsDisplay()
    }

    func placeholderRectForBounds(bounds: CGRect) -> CGRect {
        var x = contentInset.left + 4.0
        var y = contentInset.top  + 9.0
        let w = frame.size.width - contentInset.left - contentInset.right - 16.0
        let h = frame.size.height - contentInset.top - contentInset.bottom - 16.0

        if let style = self.typingAttributes[NSAttributedString.Key.paragraphStyle] as? NSParagraphStyle {
            x += style.headIndent
            y += style.firstLineHeadIndent
        }
        return CGRect(x: x, y: y, width: w, height: h)
    }

    override func draw(_ rect: CGRect) {
        if text!.isEmpty && !placeholderText.isEmpty {
            let paragraphStyle = NSMutableParagraphStyle()
            paragraphStyle.alignment = textAlignment
            let attributes: [NSAttributedString.Key: Any] = [
            NSAttributedString.Key(rawValue: NSAttributedString.Key.font.rawValue) : font!,
            NSAttributedString.Key(rawValue: NSAttributedString.Key.foregroundColor.rawValue) : placeholderColor,
            NSAttributedString.Key(rawValue: NSAttributedString.Key.paragraphStyle.rawValue)  : paragraphStyle]

            placeholderText.draw(in: placeholderRectForBounds(bounds: bounds), withAttributes: attributes)
        }
        super.draw(rect)
    }
}

一个更简单的方法是创建一个次要的UITextView，它具有与原始文本视图相同的所有属性，除了不同的textColor，并带有约束以确保它们保持对齐。然后当任何字符进入主文本视图时，隐藏克隆文本视图，否则显示带有一些文本的克隆文本视图。

这可以通过几种方式实现，但相对简单的方法是子类化UITextView并将所有这些逻辑保留在子类中。

所以，子类UITextView并允许它惰性地创建它的占位符视图

接口文件:

@interface FOOTextView : UITextView <UITextViewDelegate>

@property (nonatomic, copy) NSString *placeholderText;

- (void)checkPlaceholder;

@end

实现文件:

#import "FOOTextView.h"

@interface FOOTextView ()

@property (nonatomic, strong) UITextView *placeholderTextView;

@end

@implementation FOOTextView

- (void)checkPlaceholder {
    // Hide the placeholder text view if we've got any text
    self.placeholderTextView.hidden = (self.text.length > 0 || self.attributedText.length > 0);
}

- (void)setPlaceholderText:(NSString *)placeholderText {
    _placeholderText = [placeholderText copy];

    // Setup the placeholder text view if we haven't already
    [self setupPlaceholderTextView];

    // Apply the placeholder text to the placeholder text view
    self.placeholderTextView.text = placeholderText;
}

- (void)setupPlaceholderTextView {
    if (!self.placeholderTextView) {

        // Setup the place holder text view, duplicating our visual setup
        self.placeholderTextView = [[UITextView alloc] initWithFrame:CGRectZero];
        self.placeholderTextView.translatesAutoresizingMaskIntoConstraints = NO;
        self.placeholderTextView.textColor = self.placeholderTextColor ? self.placeholderTextColor : [UIColor colorWithRed:199.f/255.f green:199.f/255.f blue:205.f/255.f alpha:1.f];
        self.placeholderTextView.userInteractionEnabled = NO;
        self.placeholderTextView.font = self.font;
        self.placeholderTextView.textAlignment = self.textAlignment;
        self.placeholderTextView.backgroundColor = self.backgroundColor;
        self.placeholderTextView.editable = NO;

        // Our background color must be clear for the placeholder text view to show through
        self.backgroundColor = [UIColor clearColor];

        // Insert the placeholder text view into our superview, below ourself so it shows through
        [self.superview insertSubview:self.placeholderTextView belowSubview:self];

        // Setup constraints to ensure the placeholder text view stays aligned with us
        NSLayoutConstraint *constraintCenterX = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterX multiplier:1.f constant:0.f];
        NSLayoutConstraint *constraintCenterY = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterY multiplier:1.f constant:0.f];
        NSLayoutConstraint *constraintWidth = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeWidth multiplier:1.f constant:0.f];
        NSLayoutConstraint *constraintHeight = [NSLayoutConstraint constraintWithItem:self.placeholderTextView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeHeight multiplier:1.f constant:0.f];
        NSArray *constraints = @[constraintCenterX, constraintCenterY, constraintWidth, constraintHeight];
        [self.superview addConstraints:constraints];

    }
}

- (void)setPlaceholderTextColor:(UIColor *)placeholderTextColor {
    _placeholderTextColor = placeholderTextColor;
    self.placeholderTextView.textColor = _placeholderTextColor;
}

- (void)setBackgroundColor:(UIColor *)backgroundColor {
    // We don't want a background color ourselves, instead we want our placeholder text view to have the desired background color
    [self.placeholderTextView setBackgroundColor:backgroundColor];
}

- (void)removeFromSuperview {
    // Ensure we also remove our placeholder text view
    [self.placeholderTextView removeFromSuperview];
    self.placeholderTextView = nil;
    [super removeFromSuperview];
}

#pragma mark - Text View Delegation 
- (void)textViewDidChange:(UITextView *)textView {
    [self checkPlaceholder];
}

@end

使用上面的类，如果你设置了一个FOOTextView的委托实例到它自己，一切都将开箱工作:

FOOTextView *myTextView = ...
myTextView.placeholderText = @"What's on your mind?";
myTextView.placeholderTextColor = [UIColor lightGrayColor];
myTextView.delegate = myTextView;

如果你想另一个对象接管作为委托，那么你只需要在textViewDidChange: delegate方法中调用文本视图的checkPlaceholder方法，例如;

FOOTextView *myTextView = ...
myTextView.placeholderText = @"What's on your mind?";
myTextView.placeholderTextColor = [UIColor lightGrayColor];
myTextView.delegate = self;
self.myTextView = myTextView;

- (void)textViewDidChange:(UITextView *)textView {
    // Call the checkPlaceholder method to update the visuals
    [self.myTextView checkPlaceholder];
}

如果有人需要Swift的解决方案:

添加UITextViewDelegate到类中

var placeHolderText = "Placeholder Text..."

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

func textViewShouldBeginEditing(textView: UITextView) -> Bool {

    self.textView.textColor = .black

    if(self.textView.text == placeHolderText) {
        self.textView.text = ""
    }

    return true
}

func textViewDidEndEditing(textView: UITextView) {
    if(textView.text == "") {
        self.textView.text = placeHolderText
        self.textView.textColor = .lightGray
    }
}

override func viewWillAppear(animated: Bool) {

    if(currentQuestion.answerDisplayValue == "") {
        self.textView.text = placeHolderText
        self.textView.textColor = .lightGray
    } else {
        self.textView.text = "xxx" // load default text / or stored 
        self.textView.textColor = .black
    }
}

在看完所有答案后，我意识到我需要一些简单的，同时可重用的东西，这样我就可以在我的项目中为所有uitextview添加相同的功能。最后我得到了以下代码:

extension UITextView {

// MARK: TextView PlaceHolderLabel Setup

func createPlaceHolderLabel(with text: String) {
    let lbl = UILabel()
    self.addSubview(lbl)

// Add your constraints here

    lbl.text = text
    lbl.textColor = .lightGray
}

// My Textview contains only one UILabel, and for my use case the below code works, tweak it according to your use case

// Lastly two methods to toggle between show and hide the placeholder label

func hidePlaceHolderLabel() {
    guard let lbl = self.subviews.first(where: { $0 is UILabel }) else { return }
    lbl.isHidden = true
}

func showPlaceHolderLabel() {
    guard let lbl = self.subviews.first(where: { $0 is UILabel }) else { return }
    lbl.isHidden = false
}

}

当UILabel作为子视图添加到UITextView时，textView游标位置和UILabel位置将不匹配，因此在占位符文本之前留下一个空间

class ViewController: UIViewController, UITextViewDelegate {
    var textView: UITextView!

override func viewDidLoad() {
    super.viewDidLoad()
    view.addSubview(textView)
    // Also setup textView constraints as per your need
    // Add placeholder to your textView
    // Leave one space before placeholder string
    textView.createPlaceHolderLabel(with: " Address")
    textView.delegate = self
}

然后在textViewdidChange方法中添加以下代码

func textViewDidChange(_ textView: UITextView) {
    if textView.text.isEmpty {
        textView.showPlaceHolderLabel()
    } else {
        textView.hidePlaceHolderLabel()
    }
}

它可以在所有uitextview中重用。

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()
    }
}

你可以在UITextView上设置标签

[UITextView addSubView:lblPlaceHoldaer];

并隐藏在TextViewdidChange方法上。

这是一个简单易行的方法。