你也可以创建一个新的类TextViewWithPlaceholder作为UITextView的子类。

(这段代码有点粗糙——但我认为它在正确的轨道上。)

@interface TextViewWithPlaceholder : UITextView
{

    NSString *placeholderText;  // make a property
    UIColor *placeholderColor;  // make a property
    UIColor *normalTextColor;   // cache text color here whenever you switch to the placeholderColor
}

- (void) setTextColor: (UIColor*) color
{
   normalTextColor = color;
   [super setTextColor: color];
}

- (void) updateForTextChange
{
    if ([self.text length] == 0)
    { 
        normalTextColor = self.textColor;
        self.textColor = placeholderColor;
        self.text = placeholderText;
    }
    else
    {
        self.textColor = normalTextColor;
    }

}

在委托中，添加以下内容:

- (void)textViewDidChange:(UITextView *)textView
{
    if ([textView respondsToSelector: @selector(updateForTextChange)])
    {
        [textView updateForTextChange];
    }

}

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。

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。

我找到了自己的解决方案

- (void)textViewDidBeginEditing:(UITextView *)textView
{
    if ([textView.text isEqualToString:PLACEHOLDER_TEXT])
    {
        textView.textColor = [UIColor lightGrayColor];
        dispatch_async(dispatch_get_main_queue(), ^
                       {
                           textView.selectedRange = NSMakeRange(0, 0);
                       });
    }
    else
    {
        textView.textColor = [UIColor blackColor];
    }

    [textView becomeFirstResponder];
}

- (void)textViewDidEndEditing:(UITextView *)textView
{
    if ([textView.text isEqualToString:@""])
    {
        textView.text = PLACEHOLDER_TEXT;
        textView.textColor = [UIColor lightGrayColor];
    }

    [textView resignFirstResponder];
}

- (BOOL)textView:(UITextView *)textView
shouldChangeTextInRange:(NSRange)range
 replacementText:(NSString *)text
{
    if (range.location == 0 && range.length == [[textView text] length] && [text isEqualToString:@""])
    {
        textView.text = PLACEHOLDER_TEXT;
        textView.textColor = [UIColor lightGrayColor];

        dispatch_async(dispatch_get_main_queue(), ^
                       {
                           textView.selectedRange = NSMakeRange(0, 0);
                       });

        return NO;
    }

    if ([textView.text isEqualToString:PLACEHOLDER_TEXT])
    {
        textView.text = @"";
        textView.textColor = [UIColor blackColor];
    }

    return YES;
}

简单的方法，使用以下UITextViewDelegate方法在UITextView中创建占位符文本:

- (void)textViewDidBeginEditing:(UITextView *)textView
{
    if ([textView.text isEqualToString:@"placeholder text here..."]) {
         textView.text = @"";
         textView.textColor = [UIColor blackColor]; //optional
    }
    [textView becomeFirstResponder];
}

- (void)textViewDidEndEditing:(UITextView *)textView
{
    if ([textView.text isEqualToString:@""]) {
        textView.text = @"placeholder text here...";
        textView.textColor = [UIColor lightGrayColor]; //optional
    }
    [textView resignFirstResponder];
}

只需要记住在创建时使用准确的文本设置myUITextView即可。

UITextView *myUITextView = [[UITextView alloc] init];
myUITextView.delegate = self;
myUITextView.text = @"placeholder text here...";
myUITextView.textColor = [UIColor lightGrayColor]; //optional

在包含这些方法之前，让父类成为一个UITextViewDelegate。

@interface MyClass () <UITextViewDelegate>
@end

Swift 3.1代码

func textViewDidBeginEditing(_ textView: UITextView) 
{
    if (textView.text == "placeholder text here..." && textView.textColor == .lightGray)
    {
        textView.text = ""
        textView.textColor = .black
    }
    textView.becomeFirstResponder() //Optional
}

func textViewDidEndEditing(_ textView: UITextView)
{
    if (textView.text == "")
    {
        textView.text = "placeholder text here..."
        textView.textColor = .lightGray
    }
    textView.resignFirstResponder()
}

只需要记住在创建时使用准确的文本设置myUITextView即可。

 let myUITextView = UITextView.init()
 myUITextView.delegate = self
 myUITextView.text = "placeholder text here..."
 myUITextView.textColor = .lightGray

在包含这些方法之前，让父类成为一个UITextViewDelegate。

class MyClass: UITextViewDelegate
{

}