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…)

这里有一个更简单的解决方案，它的行为完全像UITextField的占位符，但不需要绘制自定义视图，或辞职第一响应器。

- (void) textViewDidChange:(UITextView *)textView{

    if (textView.text.length == 0){
        textView.textColor = [UIColor lightGrayColor];
        textView.text = placeholderText;
        [textView setSelectedRange:NSMakeRange(0, 0)];
        isPlaceholder = YES;

    } else if (isPlaceholder && ![textView.text isEqualToString:placeholderText]) {
        textView.text = [textView.text substringToIndex:1];
        textView.textColor = [UIColor blackColor];
        isPlaceholder = NO;
    }

}

(else if语句中的第二个检查是针对没有输入任何内容且用户按下退格键的情况)

只需要将你的类设置为UITextViewDelegate。在viewDidLoad中，你应该这样初始化

- (void) viewDidLoad{
    // initialize placeholder text
    placeholderText = @"some placeholder";
    isPlaceholder = YES;
    self.someTextView.text = placeholderText;
    self.someTextView.textColor = [UIColor lightGrayColor];
    [self.someTextView setSelectedRange:NSMakeRange(0, 0)];

    // assign UITextViewDelegate
    self.someTextView.delegate = self;
}

斯威夫特3.1

在尝试了所有快速的答案之后，这个答案将为我节省3个小时的研究时间。希望这能有所帮助。

确保你的textField(不管你有什么自定义名称)指向它在Storyboard中的委托，并且有一个@IBOutlet和你的customtextfield 将以下内容添加到viewDidLoad()中，加载视图时会出现:

告诉我什么看起来是占位符:

yourCustomTextField = "Start typing..." 
yourCustomTextField.textColor = .lightGray

在viewDidLoad外部但在同一个类内部添加以下声明:UIViewController, UITextViewDelegate, UINavigationControllerDelegate

这段代码将使yourCustomTextField在输入textField时消失:

func textViewDidBeginEditing (_ textView: UITextView) { 

    if (textView.text == "Start typing...") {

        textView.text = ""
        textView.textColor = .black
    }

    textView.becomeFirstResponder()
}

func textViewDidEndEditing(_ textView: UITextView) {
    if (textView.text == "") {

        textView.text = "Start typing..."
        textView.textColor = .lightGray
    }

    textView.resignFirstResponder()
}

我是这样做的:

UITextView2.h

#import <UIKit/UIKit.h>

@interface UITextView2 : UITextView <UITextViewDelegate> {
 NSString *placeholder;
 UIColor *placeholderColor;
}

@property(nonatomic, retain) NSString *placeholder;
@property(nonatomic, retain) UIColor *placeholderColor;

-(void)textChanged:(NSNotification*)notif;

@end

UITextView2.m

@implementation UITextView2

@synthesize placeholder, placeholderColor;

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        [self setPlaceholder:@""];
        [self setPlaceholderColor:[UIColor lightGrayColor]];
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

-(void)textChanged:(NSNotification*)notif {
    if ([[self placeholder] length]==0)
        return;
    if ([[self text] length]==0) {
        [[self viewWithTag:999] setAlpha:1];
    } else {
        [[self viewWithTag:999] setAlpha:0];
    }

}

- (void)drawRect:(CGRect)rect {
    if ([[self placeholder] length]>0) {
        UILabel *l = [[UILabel alloc] initWithFrame:CGRectMake(8, 8, 0, 0)];
        [l setFont:self.font];
        [l setTextColor:self.placeholderColor];
        [l setText:self.placeholder];
        [l setAlpha:0];
        [l setTag:999];
        [self addSubview:l];
        [l sizeToFit];
        [self sendSubviewToBack:l];
        [l release];
    }
    if ([[self text] length]==0 && [[self placeholder] length]>0) {
        [[self viewWithTag:999] setAlpha:1];
    }
    [super drawRect:rect];
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    [super dealloc];
}


@end

更简单，并且仍然考虑到用户在某些时候输入的一些文本

BOOL placeHolderTextVisible;

在viewDidLoad上，设置它为YES(或DidMoveToSuperview，或awakeFromNib)

然后,在 - (BOOL) textView:(UITextView*)textView shouldBeginEditing

    - (BOOL)textViewShouldBeginEditing:(UITextView *)textView;
{
   if (placeHolderTextVisible) {
    placeHolderTextVisible = NO;
    textView.text = @"";
   }
 return YES;
}

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
    }
}