Fix: PasswordBox does not accept PasswordChar as input

src/Wpf.Ui/Controls/PasswordBox/PasswordBox.cs

@@ -16,8 +16,9 @@ namespace Wpf.Ui.Controls;
 /// <summary>
 /// The modified password control.
 /// </summary>
-public class PasswordBox : Wpf.Ui.Controls.TextBox
+public partial class PasswordBox : Wpf.Ui.Controls.TextBox
 {
+    private readonly PasswordHelper _passwordHelper;
     private bool _lockUpdatingContents;
 
     /// <summary>Identifies the <see cref="Password"/> dependency property.</summary>
@@ -112,6 +113,7 @@ public event RoutedEventHandler PasswordChanged
     public PasswordBox()
     {
         _lockUpdatingContents = false;
+        _passwordHelper = new PasswordHelper(this);
     }
 
     /// <inheritdoc />
@@ -228,47 +230,11 @@ private void UpdateTextContents(bool isTriggeredByTextInput)
         }
 
         var caretIndex = CaretIndex;
-        var selectionIndex = SelectionStart;
-        var currentPassword = Password ?? string.Empty;
-        var newPasswordValue = currentPassword;
+        var newPasswordValue = _passwordHelper.GetPassword();
 
         if (isTriggeredByTextInput)
         {
-            var currentText = Text;
-            var newCharacters = currentText.Replace(PasswordChar.ToString(), string.Empty);
-
-            if (currentText.Length < currentPassword.Length)
-            {
-                newPasswordValue = currentPassword.Remove(
-                    selectionIndex,
-                    currentPassword.Length - currentText.Length
-                );
-            }
-
-            if (newCharacters.Length > 1)
-            {
-                var index = currentText.IndexOf(newCharacters[0]);
-
-                newPasswordValue =
-                    index > newPasswordValue.Length - 1
-                        ? newPasswordValue + newCharacters
-                        : newPasswordValue.Insert(index, newCharacters);
-            }
-            else
-            {
-                for (int i = 0; i < currentText.Length; i++)
-                {
-                    if (currentText[i] == PasswordChar)
-                    {
-                        continue;
-                    }
-
-                    newPasswordValue =
-                        currentText.Length == newPasswordValue.Length
-                            ? newPasswordValue.Remove(i, 1).Insert(i, currentText[i].ToString())
-                            : newPasswordValue.Insert(i, currentText[i].ToString());
-                }
-            }
+            newPasswordValue = _passwordHelper.GetNewPassword();
         }
 
         _lockUpdatingContents = true;

src/Wpf.Ui/Controls/PasswordBox/PasswordHelper.cs

@@ -0,0 +1,118 @@
+// This Source Code Form is subject to the terms of the MIT License.
+// If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+// Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+// All Rights Reserved.
+
+using System.Diagnostics;
+
+// ReSharper disable once CheckNamespace
+namespace Wpf.Ui.Controls;
+
+#pragma warning disable SA1601
+
+public partial class PasswordBox
+{
+    private class PasswordHelper
+    {
+        private readonly PasswordBox _passwordBox;
+        private string _currentText;
+        private string _newPasswordValue;
+        private string _currentPassword;
+
+        public PasswordHelper(PasswordBox passwordBox)
+        {
+            _passwordBox = passwordBox;
+            _currentText = string.Empty;
+            _newPasswordValue = string.Empty;
+            _currentPassword = string.Empty;
+        }
+
+        public string GetNewPassword()
+        {
+            _currentPassword = GetPassword();
+            _newPasswordValue = _currentPassword;
+            _currentText = _passwordBox.Text;
+            var selectionIndex = _passwordBox.SelectionStart;
+            var passwordChar = _passwordBox.PasswordChar;
+            var newCharacters = _currentText.Replace(passwordChar.ToString(), string.Empty);
+            bool isDeleted = false;
+
+            if (IsDeleteOption())
+            {
+                _newPasswordValue = _currentPassword.Remove(
+                    selectionIndex,
+                    _currentPassword.Length - _currentText.Length
+                );
+                isDeleted = true;
+            }
+
+            switch (newCharacters.Length)
+            {
+                case > 1:
+                {
+                    var index = _currentText.IndexOf(newCharacters[0]);
+
+                    _newPasswordValue =
+                        index > _newPasswordValue.Length - 1
+                            ? _newPasswordValue + newCharacters
+                            : _newPasswordValue.Insert(index, newCharacters);
+                    break;
+                }
+
+                case 1:
+                {
+                    for (int i = 0; i < _currentText.Length; i++)
+                    {
+                        if (_currentText[i] == passwordChar)
+                        {
+                            continue;
+                        }
+
+                        UpdatePasswordWithInputCharacter(i, _currentText[i].ToString());
+                        break;
+                    }
+
+                    break;
+                }
+
+                case 0 when !isDeleted:
+                {
+                    // The input is a PasswordChar, which is to be inserted at the designated position.
+                    int insertIndex = selectionIndex - 1;
+                    UpdatePasswordWithInputCharacter(insertIndex, passwordChar.ToString());
+                    break;
+                }
+            }
+
+            return _newPasswordValue;
+        }
+
+        private void UpdatePasswordWithInputCharacter(int insertIndex, string insertValue)
+        {
+            Debug.Assert(_currentText == _passwordBox.Text, "_currentText == _passwordBox.Text");
+
+            if (_currentText.Length == _newPasswordValue.Length)
+            {
+                // If it's a direct character replacement, remove the existing one before inserting the new one.
+                _newPasswordValue = _newPasswordValue.Remove(insertIndex, 1).Insert(insertIndex, insertValue);
+            }
+            else
+            {
+                _newPasswordValue = _newPasswordValue.Insert(insertIndex, insertValue);
+            }
+        }
+
+        private bool IsDeleteOption()
+        {
+            Debug.Assert(_currentText == _passwordBox.Text, "_currentText == _passwordBox.Text");
+            Debug.Assert(
+                _currentPassword == _passwordBox.Password,
+                "_currentPassword == _passwordBox.Password"
+            );
+
+            return _currentText.Length < _currentPassword.Length;
+        }
+
+        public string GetPassword() => _passwordBox.Password ?? string.Empty;
+    }
+}