我不知道为什么人们会把这个问题复杂化....这是相当直接和简单的。下面是UITextView的一个子类，它提供了所请求的功能。

- (void)customInit
{
    self.contentMode = UIViewContentModeRedraw;
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textChanged:) name:UITextViewTextDidChangeNotification object:nil];
}

    - (void)textChanged:(NSNotification *)notification
    {
        if (notification.object == self) {
            if(self.textStorage.length != 0 || !self.textStorage.length) {
                [self setNeedsDisplay];
            }
        }
    }


    #pragma mark - Setters

    - (void)setPlaceholderText:(NSString *)placeholderText withFont:(UIFont *)font
    {
        self.placeholderText = placeholderText;
        self.placeholderTextFont = font;

    }



    - (void)drawRect:(CGRect)rect
    {
        [super drawRect:rect];
        [[UIColor lightGrayColor] setFill];

        if (self.textStorage.length != 0) {
            return;
        }

        CGRect inset = CGRectInset(rect, 8, 8);//Default rect insets for textView
        NSDictionary *attributes =  @{NSFontAttributeName: self.placeholderTextFont, NSForegroundColorAttributeName: [UIColor grayColor]};
        [self.placeholderText drawInRect:inset withAttributes:attributes];
    }`

斯威夫特5.2

独立的类

如果你想要一个类，你可以在任何地方使用，因为它是自包含的

import UIKit
class PlaceHolderTextView:UITextView, UITextViewDelegate{
var placeholderText = "placeholderText"

override func willMove(toSuperview newSuperview: UIView?) {
    textColor = .lightText
    delegate = self
}

func textViewDidBeginEditing(_ textView: UITextView) {
    if textView.text == placeholderText{
        placeholderText = textView.text
        textView.text = ""
        textView.textColor = .darkText
    }
}

func textViewDidEndEditing(_ textView: UITextView) {
    if textView.text == ""{
        textView.text = placeholderText
        textColor = .lightText
    }
}    
}

这里的关键是willMove(toSuperView:)函数，因为它允许你在添加到另一个视图的层次结构之前设置视图(类似于ViewControllers中的viewDidLoad/viewWillAppear)

斯威夫特

这是一个Swiftui TextView使用UIVIewRepresentable，具有占位符功能和边界颜色

struct TextView: UIViewRepresentable {

@Binding var text: String
var placeholderText: String
var textStyle: UIFont.TextStyle

func makeUIView(context: Context) -> UITextView {
    let textView = UITextView()

    textView.font = UIFont.preferredFont(forTextStyle: textStyle)
    textView.autocapitalizationType = .sentences
    textView.isSelectable = true
    textView.isUserInteractionEnabled = true
    textView.delegate = context.coordinator
    textView.layer.borderWidth = 0.6
    textView.layer.borderColor = UIColor.lightGray.cgColor
    textView.layer.cornerRadius = 10
    textView.text = placeholderText
    textView.textColor = UIColor.lightGray
    return textView
}

func updateUIView(_ uiView: UITextView, context: Context) {
    uiView.text = text
    uiView.font = UIFont.preferredFont(forTextStyle: textStyle)
}

func makeCoordinator() -> Coordinator {
    Coordinator(self)
}
 
class Coordinator: NSObject, UITextViewDelegate {
    var parent: TextView
 
    init(_ parent: TextView) {
        self.parent = parent
    }
 
    func textViewDidChange(_ textView: UITextView) {
        self.parent.text = textView.text
    }
    
    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == UIColor.lightGray {
            textView.text = nil
            textView.textColor = UIColor.black
        }
    }
    
    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
            textView.text = self.parent.placeholderText
            textView.textColor = UIColor.lightGray
        }
    }
}

}

然后在你的视图中你可以这样使用它

TextView(text: self.$viewModel.addPostCommentText, placeholderText: "Share your story about this cash", textStyle: .body)
                .padding()
                .frame(height: 150)

可能是UITextView占位符实现的最简单的开箱即用的解决方案，不会遭受:

使用UILabel而不是UITextView，这可能会有不同的表现 切换到和从占位符“UITextView”拷贝，将捕获第一个键入的字符将从主UITextView控件丢失 打乱主UITextView控件的文本内容，将占位符替换为空字符串或第一个键入的字符。边界情况是，如果用户输入占位符文本，一些建议的实现将把它作为一个占位符本身。

斯威夫特5:

import UIKit
import SnapKit
import RxSwift
import RxCocoa

class TextAreaView: UIView {
    let textArea = UITextView()
    let textAreaPlaceholder = UITextView()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonSetup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        commonSetup()
    }
    
    private func commonSetup() {
        
        addSubview(textAreaPlaceholder)
        addSubview(textArea)
        
        textArea.isScrollEnabled = false
        textArea.delegate = self

        textAreaPlaceholder.isScrollEnabled = false
        textAreaPlaceholder.textColor = UIColor.lightGray
        
        textArea.snp.makeConstraints { make in
            make.top.bottom.leading.trailing.equalToSuperview()
        }

        textAreaPlaceholder.snp.makeConstraints { make in
            make.top.bottom.leading.trailing.equalTo(textArea.snp.top)
        }

        textAreaPlaceholder.text = "Placeholder"
        
        updatePlaceholder()
    }
    
    func updatePlaceholder() {
        if textArea.text.count > 0 {
            textArea.alpha = 1.0
        } else {
            textArea.alpha = 0.0
        }
    }
}

extension TextAreaView: UITextViewDelegate {
    func textViewDidChange(_ textView: UITextView) {
        updatePlaceholder()
    }
}

由于声誉问题，我不能发表评论。在@clearlight answer中增加一个委托需求。

func textViewDidBeginEditing(_ textView: UITextView) { 
        cell.placeholderLabel.isHidden = !textView.text.isEmpty
}

是需要

因为textViewDidChange不是第一次被调用

斯威夫特3.2

extension EditProfileVC:UITextViewDelegate{

    func textViewDidBeginEditing(_ textView: UITextView) {
        if textView.textColor == UIColor.lightGray {
            textView.text = nil
            textView.textColor = UIColor.black
       }
    }
    func textViewDidEndEditing(_ textView: UITextView) {
        if textView.text.isEmpty {
            textView.text = "Placeholder"
            textView.textColor = UIColor.lightGray
        }
    }
}

首先，当用户开始编辑textViewDidBeginEditing调用，然后检查如果文本灰色的颜色意味着用户没有写任何东西，然后设置为textview nil，并将用户文本的颜色更改为黑色。

当用户端编辑textViewDidEndEditing是调用和检查如果用户没有写任何在textview然后文本设置为灰色与文本“占位符”