WPF实现授权码显示密文并支持换行

using System;
using System.Diagnostics;
using System.Text;
using System.Windows;
using System.Windows.Controls;

namespace WpfTextOrPasswordBox
{
    public class MultiLinePasswordBox : TextBox
    {
        private StringBuilder passwordBuilder = new StringBuilder();
        private string previousText = string.Empty;
        private bool isUpdating = false;

        public char PasswordChar
        {
            get { return (char)GetValue(PasswordCharProperty); }
            set { SetValue(PasswordCharProperty, value); }
        }

        public static readonly DependencyProperty PasswordCharProperty =
            DependencyProperty.Register("PasswordChar", typeof(char), typeof(MultiLinePasswordBox), new PropertyMetadata('●'));


        public string PlainText
        {
            get { return (string)GetValue(PlainTextProperty); }
            set { SetValue(PlainTextProperty, value); }
        }

        public static readonly DependencyProperty PlainTextProperty =
            DependencyProperty.Register("PlainText", typeof(string), typeof(MultiLinePasswordBox), new PropertyMetadata(string.Empty));


        public MultiLinePasswordBox()
        {
            AcceptsReturn = true;
            TextWrapping = TextWrapping.Wrap;
            VerticalScrollBarVisibility = ScrollBarVisibility.Auto;
            TextChanged += PasswordTextBox_TextChanged;
        }

        private void PasswordTextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (isUpdating)
                return;

            isUpdating = true;
            var caretIndex = CaretIndex;
            var input = Text;
            if (string.IsNullOrWhiteSpace(Text))
            {
                passwordBuilder.Clear();
            }
            else
            {
                var s = passwordBuilder.Length;
                int lengthDifference = input.Length - previousText.Length;
                if (lengthDifference > 0)
                {
                    var newText = input.Substring(caretIndex - lengthDifference, lengthDifference);
                    passwordBuilder.Insert(caretIndex - lengthDifference, newText);
                }
                else if (lengthDifference < 0)
                {
                    passwordBuilder.Remove(caretIndex, Math.Abs(lengthDifference));
                    if (passwordBuilder[caretIndex - 1].ToString() != input)
                    {
                        var index = passwordBuilder.ToString().IndexOf(passwordBuilder[caretIndex - 1]);
                        passwordBuilder.Replace(passwordBuilder[caretIndex - 1], input.Last());
                    }
                }
                var maskedText = CreateMaskedTextWithLineBreaks(passwordBuilder.ToString());
                TextChanged -= PasswordTextBox_TextChanged;
                Text = maskedText;
                TextChanged += PasswordTextBox_TextChanged;
            }
            previousText = Text;
            CaretIndex = caretIndex;
            PlainText = passwordBuilder.ToString();
            isUpdating = false;
        }

        private string CreateMaskedTextWithLineBreaks(string text)
        {
            var maskedText = new StringBuilder();
            foreach (char c in text)
            {
                if (c == '\r' || c == '\n')
                    maskedText.Append(c);
                else
                    maskedText.Append(PasswordChar.ToString());
            }
            return maskedText.ToString();
        }
    }
}

<wd:Window
    x:Class="WpfTextOrPasswordBox.MultiLinePasswordBoxSample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:local="clr-namespace:WpfTextOrPasswordBox"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:wd="https://github.com/WPFDevelopersOrg/WPFDevelopers"
    Title="MultiLinePasswordBoxSample - WPF开发者"
    Width="800"
    Height="450"
    WindowStartupLocation="CenterScreen"
    mc:Ignorable="d">
    <Grid>
        <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBlock Margin="0,20">
                <Run Text="明文：" />
                <Run Text="{Binding ElementName=myMultiLinePasswordBox, Path=PlainText}" />
            </TextBlock>
            <local:MultiLinePasswordBox
                x:Name="myMultiLinePasswordBox"
                Width="200"
                Height="60"
                wd:ElementHelper.CornerRadius="3"
                wd:ElementHelper.Watermark="请输入授权码" />
        </StackPanel>
    </Grid>
</wd:Window>