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。

简单的Swift 3解决方案

添加UITextViewDelegate到类中

设置你的textview .delegate = self

创建placeholderLabel和位置它在你的textview

现在动画placeholderLabel。alpha在textViewDidChange:

  func textViewDidChange(_ textView: UITextView) {
    let newAlpha: CGFloat = textView.text.isEmpty ? 1 : 0
    if placeholderLabel.alpha != newAlpha {
      UIView.animate(withDuration: 0.3) {
        self.placeholderLabel.alpha = newAlpha
      }
    }
  }

你可能不得不使用placeholderLabel位置来设置它，但这应该不会太难

Jason的答案在iOS7中看起来有点不对劲，通过调整_placeHolderLabel的偏移量来修复它:

- (void)drawRect:(CGRect)rect
{
    if( [[self placeholder] length] > 0 )
    {
        if (_placeHolderLabel == nil )
        {
            if ([[UIDevice currentDevice].systemVersion floatValue] >= 7)
                _placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectMake(4,8,self.bounds.size.width - 8,0)];
            else
                _placeHolderLabel = [[UILabel alloc] initWithFrame:CGRectMake(8,8,self.bounds.size.width - 16,0)];
            _placeHolderLabel.lineBreakMode = NSLineBreakByWordWrapping;
            _placeHolderLabel.numberOfLines = 0;
            _placeHolderLabel.font = self.font;
            _placeHolderLabel.backgroundColor = [UIColor clearColor];
            _placeHolderLabel.textColor = self.placeholderColor;
            _placeHolderLabel.alpha = 0;
            _placeHolderLabel.tag = 999;
            [self addSubview:_placeHolderLabel];
        }

        _placeHolderLabel.text = self.placeholder;
        [_placeHolderLabel sizeToFit];
        [self sendSubviewToBack:_placeHolderLabel];
    }

    if( [[self text] length] == 0 && [[self placeholder] length] > 0 )
    {
        [[self viewWithTag:999] setAlpha:1];
    }

    [super drawRect:rect];
}

这个帖子已经有了很多答案，但这里是我更喜欢的版本。

它扩展了现有的UITextView类，因此很容易重用，并且它不拦截像textViewDidChange这样的事件(这可能会破坏用户的代码，如果他们已经在其他地方拦截了这些事件)。

使用我的代码(如下所示)，你可以很容易地添加一个占位符到任何你的UITextViews像这样:

self.textViewComments.placeholder = @"(Enter some comments here.)";

当你设置这个新的占位符值时，它会悄悄地在你的UITextView上添加一个UILabel，然后在必要时隐藏/显示它:

好的，要做这些改变，添加一个包含以下代码的"UITextViewHelper.h"文件:

//  UITextViewHelper.h
//  Created by Michael Gledhill on 13/02/15.

#import <Foundation/Foundation.h>

@interface UITextView (UITextViewHelper)

@property (nonatomic, strong) NSString* placeholder;
@property (nonatomic, strong) UILabel* placeholderLabel;
@property (nonatomic, strong) NSString* textValue;

-(void)checkIfNeedToDisplayPlaceholder;

@end

…和一个UITextViewHelper。M文件包含:

//  UITextViewHelper.m
//  Created by Michael Gledhill on 13/02/15.
//
//  This UITextView category allows us to easily display a PlaceHolder string in our UITextView.
//  The downside is that, your code needs to set the "textValue" rather than the "text" value to safely set the UITextView's text.
//
#import "UITextViewHelper.h"
#import <objc/runtime.h>

@implementation UITextView (UITextViewHelper)

#define UI_PLACEHOLDER_TEXT_COLOR [UIColor colorWithRed:170.0/255.0 green:170.0/255.0 blue:170.0/255.0 alpha:1.0]

@dynamic placeholder;
@dynamic placeholderLabel;
@dynamic textValue;

-(void)setTextValue:(NSString *)textValue
{
    //  Change the text of our UITextView, and check whether we need to display the placeholder.
    self.text = textValue;
    [self checkIfNeedToDisplayPlaceholder];
}
-(NSString*)textValue
{
    return self.text;
}

-(void)checkIfNeedToDisplayPlaceholder
{
    //  If our UITextView is empty, display our Placeholder label (if we have one)
    if (self.placeholderLabel == nil)
        return;

    self.placeholderLabel.hidden = (![self.text isEqualToString:@""]);
}

-(void)onTap
{
    //  When the user taps in our UITextView, we'll see if we need to remove the placeholder text.
    [self checkIfNeedToDisplayPlaceholder];

    //  Make the onscreen keyboard appear.
    [self becomeFirstResponder];
}

-(void)keyPressed:(NSNotification*)notification
{
    //  The user has just typed a character in our UITextView (or pressed the delete key).
    //  Do we need to display our Placeholder label ?
   [self checkIfNeedToDisplayPlaceholder];
}

#pragma mark - Add a "placeHolder" string to the UITextView class

NSString const *kKeyPlaceHolder = @"kKeyPlaceHolder";
-(void)setPlaceholder:(NSString *)_placeholder
{
    //  Sets our "placeholder" text string, creates a new UILabel to contain it, and modifies our UITextView to cope with
    //  showing/hiding the UILabel when needed.
    objc_setAssociatedObject(self, &kKeyPlaceHolder, (id)_placeholder, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    self.placeholderLabel = [[UILabel alloc] initWithFrame:self.frame];
    self.placeholderLabel.numberOfLines = 1;
    self.placeholderLabel.text = _placeholder;
    self.placeholderLabel.textColor = UI_PLACEHOLDER_TEXT_COLOR;
    self.placeholderLabel.backgroundColor = [UIColor clearColor];
    self.placeholderLabel.userInteractionEnabled = true;
    self.placeholderLabel.font = self.font;
    [self addSubview:self.placeholderLabel];

    [self.placeholderLabel sizeToFit];

    //  Whenever the user taps within the UITextView, we'll give the textview the focus, and hide the placeholder if necessary.
    [self addGestureRecognizer:[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onTap)]];

    //  Whenever the user types something in the UITextView, we'll see if we need to hide/show the placeholder label.
    [[NSNotificationCenter defaultCenter] addObserver:self selector: @selector(keyPressed:) name:UITextViewTextDidChangeNotification object:nil];

    [self checkIfNeedToDisplayPlaceholder];
}
-(NSString*)placeholder
{
    //  Returns our "placeholder" text string
    return objc_getAssociatedObject(self, &kKeyPlaceHolder);
}

#pragma mark - Add a "UILabel" to this UITextView class

NSString const *kKeyLabel = @"kKeyLabel";
-(void)setPlaceholderLabel:(UILabel *)placeholderLabel
{
    //  Stores our new UILabel (which contains our placeholder string)
    objc_setAssociatedObject(self, &kKeyLabel, (id)placeholderLabel, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    [[NSNotificationCenter defaultCenter] addObserver:self selector: @selector(keyPressed:) name:UITextViewTextDidChangeNotification object:nil];

    [self checkIfNeedToDisplayPlaceholder];
}
-(UILabel*)placeholderLabel
{
    //  Returns our new UILabel
    return objc_getAssociatedObject(self, &kKeyLabel);
}
@end

是的，它有很多代码，但是一旦你把它添加到你的项目中，并包含了.h文件……

#import "UITextViewHelper.h"

.．.你可以很容易地在UITextViews中使用占位符。

不过有一个问题。

如果你这样做:

self.textViewComments.placeholder = @"(Enter some comments here.)";
self.textViewComments.text = @"Ooooh, hello there";

.．.占位符将出现在文本的顶部。设置文本值时，不会调用任何常规通知，因此我不知道如何调用我的函数来决定是否显示/隐藏占位符。

解决方案是设置textValue而不是text:

self.textViewComments.placeholder = @"(Enter some comments here.)";
self.textViewComments.textValue = @"Ooooh, hello there";

或者，您可以设置文本值，然后调用checkIfNeedToDisplayPlaceholder。

self.textViewComments.text = @"Ooooh, hello there";
[self.textViewComments checkIfNeedToDisplayPlaceholder];

我喜欢这样的解决方案，因为它们“填补了”苹果提供给我们的东西和我们(作为开发者)在应用程序中实际需要的东西之间的空白。只需编写一次此代码，将其添加到“helper”.m/.h文件库中，随着时间的推移，SDK实际上开始变得不那么令人沮丧。

(我写了一个类似的帮助添加一个“清除”按钮到我的UITextViews，另一个烦人的东西存在于UITextField但不在UITextView…)

在代码行中使用它的简单方法:

取一个标签到。nib中的UITextView 将这个标签连接到你的代码， 在它。

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text{

    if (range.location>0 || text.length!=0) {
        placeholderLabel1.hidden = YES;
    }else{
        placeholderLabel1.hidden = NO;
    }
    return YES;
}

这是我的版本的UITextView与占位符支持。斯威夫特4.2 https://gist.github.com/hlung/c5dda3a0c2087e5ae6c1fce8822c4713

一个支持占位符文本的UITextView子类。它使用另一个 UILabel显示占位符，当文本为空时显示。