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];
}

你可以在textview上设置一个标签。

MyUITextView.h

@interface MyUITextView : UITextView {
    UILabel* _placeholderLabel;
}

@property(nonatomic, assign)NSString *placeholder;

MyUITextView.m

@implementation MyUITextView

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        // Create placeholder
        viewFrame = CGRectMake(0, 0, frame.size.width, 15);
        _placeholderLabel = [[UILabel alloc] initWithFrame:viewFrame];
        _placeholderLabel.textColor = [UIColor lightGrayColor];
        [self addSubview:_placeholderLabel];

        // Add text changed notification 
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
    }
    return self;
}

- (void)setPlaceholder:(NSString *)placeholder {
    _placeholderLabel.text = placeholder;
}

- (NSString*)placeholder {
    return _placeholderLabel.text;
}

#pragma mark UITextViewTextDidChangeNotification

- (void)textChanged:(NSNotification *)notification {
    _placeholderLabel.hidden = ([self.text lenght] == 0);
}

@end

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

I know there are already a lot of answers to this one, but I didn't really find any of them sufficient (at least in Swift). I needed the "placeholder" functionality of the UITextField in my UITextView (I wanted the exact behavior, including text display attributes, animations, etc, and didn't want to have to maintain this over time). I also wanted a solution that provided the same exact border as a UITextField (not an approximated one that looks sort of like it looks right now, but one that looks exactly like it and will always look exactly like it). So while I was not initially a fan of jamming an extra control into the mix, it seemed that in order to meet my goals I had to use an actual UITextField and let it do the work.

这个解决方案处理定位占位符和保持字体在两个控件之间的同步，以便占位符文本是输入到控件的文本的确切字体和位置(许多其他解决方案没有解决的问题)。

// This class is necessary to support "inset" (required to position placeholder 
// appropriately in TextView)
//
class TextField: UITextField
{
    var inset: UIEdgeInsets = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0);

    override func textRectForBounds(bounds: CGRect) -> CGRect
    {
        return UIEdgeInsetsInsetRect(bounds, inset);
    }

    override func placeholderRectForBounds(bounds: CGRect) -> CGRect
    {
        return UIEdgeInsetsInsetRect(bounds, inset);
    }
}

// This class implements a UITextView that has a UITextField behind it, where the 
// UITextField provides the border and the placeholder text functionality (so that the
// TextView looks and works like a UITextField).
//
class TextView : UITextView, UITextViewDelegate
{
    var textField = TextField();

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

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

        self.delegate = self;

        // Create a background TextField with clear (invisible) text and disabled
        self.textField.borderStyle = UITextBorderStyle.RoundedRect;
        self.textField.textColor = UIColor.clearColor();
        self.textField.userInteractionEnabled = false;

        // Align the background TextView to where text appears in the TextField, so
        // that any placeholder will be in the correct position.
        self.textField.contentVerticalAlignment = UIControlContentVerticalAlignment.Top;
        self.textField.inset = UIEdgeInsets(
            top: self.textContainerInset.top,
            left: self.textContainerInset.left + self.textContainer.lineFragmentPadding,
            bottom: self.textContainerInset.bottom,
            right: self.textContainerInset.right
        );

        // The background TextField should use the same font (for the placeholder)
        self.textField.font = self.font;

        self.addSubview(textField);
        self.sendSubviewToBack(textField);
    }

    convenience init()
    {
        self.init(frame: CGRectZero, textContainer: nil)
    }

    override var font: UIFont?
    {
        didSet
        {
            // Keep the font of the TextView and background textField in sync
            self.textField.font = self.font;
        }
    }

    var placeholder: String? = nil
    {
        didSet
        {
            self.textField.placeholder = self.placeholder;
        }
    }

    override func layoutSubviews()
    {
        super.layoutSubviews()
        // Do not scroll the background textView
        self.textField.frame = CGRectMake(0, self.contentOffset.y, self.frame.width, self.frame.height);
    }

    // UITextViewDelegate - Note: If you replace delegate, your delegate must call this
    func scrollViewDidScroll(scrollView: UIScrollView)
    {
        // Do not scroll the background textView
        self.textField.frame = CGRectMake(0, self.contentOffset.y, self.frame.width, self.frame.height);
    }

    // UITextViewDelegate - Note: If you replace delegate, your delegate must call this
    func textViewDidChange(textView: UITextView)
    {
        // Updating the text in the background textView will cause the placeholder to 
        // appear/disappear (including any animations of that behavior - since the
        // textView is doing this itself).
        self.textField.text = self.text;
    }
}

另一个解决方案

import UIKit

protocol PlaceholderTextViewDelegate: class {

    func placeholderTextViewDidChangeText(_ text: String)
    func placeholderTextViewDidEndEditing(_ text: String)
}

final class PlaceholderTextView: UITextView {

    weak var notifier: PlaceholderTextViewDelegate?
    var ignoreEnterAction: Bool = true

    var placeholder: String? {
        didSet {
            text = placeholder
            selectedRange = NSRange(location: 0, length: 0)
        }
    }

    var placeholderColor = UIColor.lightGray {
        didSet {
            if text == placeholder {
                textColor = placeholderColor
            }
        }
    }
    var normalTextColor = UIColor.lightGray

    var placeholderFont = UIFont.sfProRegular(28)

    fileprivate var placeholderLabel: UILabel?

    // MARK: - LifeCycle

    override var text: String? {
        didSet {
            if text == placeholder {
                textColor = placeholderColor
            } else {
                textColor = normalTextColor
            }
        }
    }

    init() {
        super.init(frame: CGRect.zero, textContainer: nil)
        awakeFromNib()
    }

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

    override func awakeFromNib() {
        super.awakeFromNib()

        self.delegate = self
    }
}

extension PlaceholderTextView: UITextViewDelegate {

    // MARK: - UITextViewDelegate
    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {

        if text == "" && textView.text == placeholder {
            return false
        }

        if let placeholder = placeholder,
            textView.text == placeholder,
            range.location <= placeholder.count {
            textView.text = ""
        }

        if ignoreEnterAction && text == "\n" {
            textView.resignFirstResponder()
            return false
        }
        return true
    }

    func textViewDidChange(_ textView: UITextView) {
        if let placeholder = placeholder {
            textView.text = textView.text.replacingOccurrences(of: placeholder, with: "")
        }

        if let placeholder = placeholder,
            text?.isEmpty == true {
            text = placeholder
            textColor = placeholderColor

            selectedRange = NSRange(location: 0, length: 0)
        } else {
            textColor = normalTextColor
        }

        notifier?.placeholderTextViewDidChangeText(textView.text)
    }

    func textViewDidChangeSelection(_ textView: UITextView) {
        if let placeholder = placeholder,
            text == placeholder {
            selectedRange = NSRange(location: 0, length: 0)
        }
    }

    func textViewDidEndEditing(_ textView: UITextView) {
        notifier?.placeholderTextViewDidEndEditing(textView.text)

        if let placeholder = placeholder,
            text?.isEmpty == true {
            text = placeholder
            textColor = placeholderColor
            selectedRange = NSRange(location: 0, length: 0)
        } else {
            textColor = normalTextColor
        }
    }
}

结果:

我刚刚发现，在iOS 10中，你现在可以将UITextView转换为方法的UITextField，并在方法中设置占位符。刚试过，它不需要子类化UITextView就能工作。

下面是一个对我有用的例子:

-(void)customizeTextField:(UITextField *)textField placeholder:(NSString *)pText withColor:(UIColor *)pTextColor{

        textField.attributedPlaceholder = [[NSAttributedString alloc]
                                          initWithString:pText
                                          attributes:@{NSForegroundColorAttributeName:pTextColor}];
    }

为了将它用于UITextView，你只需要将它传递给方法，使用像这样的类型转换:

[self customizeTextField:(UITextField*)_myTextView placeholder:@"Placeholder" withColor:[UIColor blackColor]];

注:经过测试，我发现这个解决方案在iOS9上也很好。但是会在iOS8.x上导致崩溃