我创建了一个实例变量来检查是否显示占位符:

BOOL showPlaceHolder;
UITextView * textView; // and also the textView

在viewDidLoad上设置:

[self setPlaceHolder]; 

下面是它的作用:

- (void)setPlaceholder
{
    textView.text = NSLocalizedString(@"Type your question here", @"placeholder");
    textView.textColor = [UIColor lightGrayColor];
    self.showPlaceHolder = YES; //we save the state so it won't disappear in case you want to re-edit it
}

我还创建了一个按钮来退出键盘。您不必这样做，但这里很酷的事情是，如果没有输入任何内容，占位符将再次显示

- (void)textViewDidBeginEditing:(UITextView *)txtView 
{
    self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Done" style:UIBarButtonItemStyleDone target:self action:@selector(resignKeyboard)];
    if (self.showPlaceHolder == YES) 
    {
        textView.textColor = [UIColor blackColor];
        textView.text = @"";
        self.showPlaceHolder = NO;
    }
}

- (void)resignKeyboard 
{
    [textView resignFirstResponder];
    //here if you created a button like I did to resign the keyboard, you should hide it
    if (textView.text.length == 0) {
        [self setPlaceholder];
    }       
}

在h课上

@interface RateCommentViewController : UIViewController<UITextViewDelegate>{IBoutlet UITextview *commentTxtView;}

在。m类

- (void)viewDidLoad{      
    commentTxtView.text = @"Comment";
    commentTxtView.textColor = [UIColor lightGrayColor];
    commentTxtView.delegate = self;
}

- (BOOL) textViewShouldBeginEditing:(UITextView *)textView
{
    commentTxtView.text = @"";
    commentTxtView.textColor = [UIColor blackColor];
    return YES;
}

-(void) textViewDidChange:(UITextView *)textView
{
    if(commentTxtView.text.length == 0){
        commentTxtView.textColor = [UIColor lightGrayColor];
        commentTxtView.text = @"Comment";
        [commentTxtView resignFirstResponder];
    }
}

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;
}

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

下面是swift 3.1的代码

原始代码由杰森乔治在第一个答案。

不要忘记设置你的自定义类的TextView在接口生成器UIPlaceHolderTextView，然后设置占位符和占位符属性。

import UIKit

@IBDesignable
class UIPlaceHolderTextView: UITextView {

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

private let uiPlaceholderTextChangedAnimationDuration: Double = 0.05
private let defaultTagValue = 999

private var placeHolderLabel: UILabel?

override func awakeFromNib() {
    super.awakeFromNib()
    NotificationCenter.default.addObserver(
        self,
        selector: #selector(textChanged),
        name: NSNotification.Name.UITextViewTextDidChange,
        object: nil
    )
}

override init(frame: CGRect, textContainer: NSTextContainer?) {
    super.init(frame: frame, textContainer: textContainer)
    NotificationCenter.default.addObserver(
        self,
        selector: #selector(textChanged),
        name: NSNotification.Name.UITextViewTextDidChange,
        object: nil
    )
}

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    NotificationCenter.default.addObserver(
        self,
        selector: #selector(textChanged),
        name: NSNotification.Name.UITextViewTextDidChange,
        object: nil
    )
}

deinit {
    NotificationCenter.default.removeObserver(
        self,
        name: NSNotification.Name.UITextViewTextDidChange,
        object: nil
    )
}

@objc private func textChanged() {
    guard !placeholder.isEmpty else {
        return
    }
    UIView.animate(withDuration: uiPlaceholderTextChangedAnimationDuration) {
        if self.text.isEmpty {
            self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(1.0)
        }
        else {
            self.viewWithTag(self.defaultTagValue)?.alpha = CGFloat(0.0)
        }
    }
}

override var text: String! {
    didSet{
        super.text = text
        textChanged()
    }
}

override func draw(_ rect: CGRect) {
    if !placeholder.isEmpty {
        if placeHolderLabel == nil {
            placeHolderLabel = UILabel.init(frame: CGRect(x: 0, y: 8, width: bounds.size.width - 16, height: 0))
            placeHolderLabel!.lineBreakMode = .byWordWrapping
            placeHolderLabel!.numberOfLines = 0
            placeHolderLabel!.font = font
            placeHolderLabel!.backgroundColor = UIColor.clear
            placeHolderLabel!.textColor = placeholderColor
            placeHolderLabel!.alpha = 0
            placeHolderLabel!.tag = defaultTagValue
            self.addSubview(placeHolderLabel!)
        }

        placeHolderLabel!.text = placeholder
        placeHolderLabel!.sizeToFit()
        self.sendSubview(toBack: placeHolderLabel!)

        if text.isEmpty && !placeholder.isEmpty {
            viewWithTag(defaultTagValue)?.alpha = 1.0
        }
    }

    super.draw(rect)
}
}