SwiftUI中如何为TextField实现数字每3位自动添加逗号分隔

你找到的代码是UIKit下UITextField的代理回调，无法直接绑定到SwiftUI原生TextField上，以下是两种可直接落地的实现方式：

不需要依赖UIKit的代理逻辑，直接监听绑定字符串的变化做实时格式化，完全兼容你现有的代码结构，逻辑和你找到的delegate代码完全对齐：

import SwiftUI

struct AmountInputView: View {
    @State private var purchaseAmount: String = ""
    // 提前初始化格式化器，避免每次输入重复创建影响性能
    private let decimalFormatter: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.maximumFractionDigits = 8
        return formatter
    }()
    
    var body: some View {
        TextField("Purchase Amount", text: $purchaseAmount)
            .padding()
            .background(Color(.tertiarySystemFill))
            .cornerRadius(9)
            .multilineTextAlignment(.center)
            .keyboardType(.decimalPad)
            .onChange(of: purchaseAmount) { inputValue in
                // 移除已有逗号，过滤非数字/小数点的非法字符
                let cleanedValue = inputValue
                    .replacingOccurrences(of: ",", with: "")
                    .components(separatedBy: CharacterSet(charactersIn: "0123456789.").inverted)
                    .joined()
                
                // 处理多小数点异常，仅保留第一个小数点
                var valueParts = cleanedValue.components(separatedBy: ".")
                if valueParts.count > 2 {
                    valueParts = [valueParts[0], valueParts[1...].joined()]
                }
                let validValue = valueParts.joined(separator: valueParts.count > 1 ? "." : "")
                
                // 处理末尾小数点、小数点后尾随0的特殊场景（避免被格式化器自动截断）
                if validValue.hasSuffix(".") {
                    guard let integerNum = decimalFormatter.number(from: String(validValue.dropLast())) else {
                        purchaseAmount = validValue
                        return
                    }
                    purchaseAmount = (decimalFormatter.string(from: integerNum) ?? "") + "."
                } else if validValue.contains("."), let decimalPart = valueParts.last, decimalPart.allSatisfy({ $0 == "0" }) {
                    guard let integerNum = decimalFormatter.number(from: valueParts[0]) else {
                        purchaseAmount = validValue
                        return
                    }
                    purchaseAmount = (decimalFormatter.string(from: integerNum) ?? "") + "." + decimalPart
                } else {
                    guard let number = decimalFormatter.number(from: validValue) else {
                        purchaseAmount = validValue.isEmpty ? "" : String(validValue.dropLast())
                        return
                    }
                    purchaseAmount = decimalFormatter.string(from: number) ?? ""
                }
            }
    }
}

注意：不要使用SwiftUI自带的TextField(_:value:format:)初始化方法实现该需求，该方法的格式化逻辑仅在输入结束、焦点离开输入框时触发，无法做到输入过程中实时插入千分位逗号。

如果你不想改写已找到的delegate逻辑，可以通过UIViewRepresentable将UITextField包装为SwiftUI组件，直接接入原有代码：

1. 首先定义可复用的格式化输入框组件：

import SwiftUI
import UIKit

struct DecimalTextField: UIViewRepresentable {
    let placeholder: String
    @Binding var text: String
    
    func makeCoordinator() -> Coordinator {
        Coordinator(parent: self)
    }
    
    func makeUIView(context: Context) -> UITextField {
        let textField = UITextField()
        textField.placeholder = placeholder
        textField.keyboardType = .decimalPad
        textField.textAlignment = .center
        textField.delegate = context.coordinator
        return textField
    }
    
    func updateUIView(_ uiView: UITextField, context: Context) {
        uiView.text = text
    }
    
    class Coordinator: NSObject, UITextFieldDelegate {
        let parent: DecimalTextField
        private let formatter: NumberFormatter = {
            let formatter = NumberFormatter()
            formatter.numberStyle = .decimal
            formatter.maximumFractionDigits = 8
            return formatter
        }()
        
        init(parent: DecimalTextField) {
            self.parent = parent
        }
        
        // 直接复用你找到的代理逻辑，仅补充绑定值同步
        func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
            if ((string == "0" || string == "") && (textField.text! as NSString).range(of: ".").location < range.location) {
                return true
            }

            let cs = NSCharacterSet(charactersIn: "0123456789.").inverted
            let filtered = string.components(separatedBy: cs)
            let component = filtered.joined(separator: "")
            let isNumeric = string == component

            if isNumeric {
                let newString = (textField.text! as NSString).replacingCharacters(in: range, with: string)
                let numberWithOutCommas = newString.replacingOccurrences(of: ",", with: "")
                let number = formatter.number(from: numberWithOutCommas)
                if number != nil {
                    var formattedString = formatter.string(from: number!)
                    if string == "." && range.location == textField.text?.count {
                        formattedString = formattedString?.appending(".")
                    }
                    textField.text = formattedString
                    // 同步值到SwiftUI绑定
                    parent.text = formattedString ?? ""
                } else {
                    textField.text = nil
                    parent.text = ""
                }
            }
            return false
        }
    }
}

2. 在业务代码中替换原有TextField即可：

struct ContentView: View {
    @State private var purchaseAmount: String = ""
    
    var body: some View {
        DecimalTextField(placeholder: "Purchase Amount", text: $purchaseAmount)
            .padding()
            .background(Color(.tertiarySystemFill))
            .cornerRadius(9)
    }
}

内容的提问来源于stack exchange，提问作者johnboumelhem