WPF 中的自定义屏蔽密码框

Question

在 iOS 中，当您在字段中输入密码时，会显示该字段的最后一个字母，但在您输入下一个字符时会被混淆。有没有办法在 WPF 中复制这种行为？

Answer 1

如果您在桌面应用程序中使用此类东西是合理的，那么您可以执行以下操作。

我们之前有类似的要求，这就是我所做的。

• 我通过从TextBox 派生并添加一个SecureString 类型的新DP 来创建一个自定义Passwordbox（与普通PasswordBox 的概念几乎相同）。通过这种方式，我们不会失去任何安全优势，并且可以根据自己的喜好自定义视觉行为。
• 现在我们可以使用 Text 的 Text 作为显示字符串，并将实际密码保存在后端 SecureString DP 中并将其绑定到 VM。
• 我们处理PreviewTextInput 和PreviewKeyDown 事件来管理控件中的所有文本更改，包括Key.Back、Key.Delete 和烦人的Key.Space（这不是通过PreviewTextInput

iOS 感觉：

为确切的 iOS 行为添加更多注意事项。

1. 仅在将新字符添加到“当前字符串的结尾”时才显示最后一个字符（FlowDirection 独立）
2. 编辑现有字符串之间的字符对掩码没有影响。
3. 显示的最后一个字符取决于计时器（如果闲置一段时间后变为“*”）
4. 在控件中禁用了所有复制粘贴操作。

在检测文本更改时可以很容易地处理前 2 个点，对于最后一个点，我们可以使用 DispatcherTimer 相应地处理显示字符串。

所以把这一切放在一起，我们最终得到：

/// <summary>
///   This class contains properties for CustomPasswordBox
/// </summary>
internal class CustomPasswordBox : TextBox {
  #region Member Variables
  /// <summary>
  ///   Dependency property to hold watermark for CustomPasswordBox
  /// </summary>
  public static readonly DependencyProperty PasswordProperty =
    DependencyProperty.Register(
      "Password", typeof(SecureString), typeof(CustomPasswordBox), new UIPropertyMetadata(new SecureString()));

  /// <summary>
  ///   Private member holding mask visibile timer
  /// </summary>
  private readonly DispatcherTimer _maskTimer;
  #endregion

  #region Constructors
  /// <summary>
  ///   Initialises a new instance of the LifeStuffPasswordBox class.
  /// </summary>
  public CustomPasswordBox() {
    PreviewTextInput += OnPreviewTextInput;
    PreviewKeyDown += OnPreviewKeyDown;
    CommandManager.AddPreviewExecutedHandler(this, PreviewExecutedHandler);
    _maskTimer = new DispatcherTimer { Interval = new TimeSpan(0, 0, 0, 1) };
    _maskTimer.Tick += (sender, args) => MaskAllDisplayText();
  }
  #endregion

  #region Commands & Properties
  /// <summary>
  ///   Gets or sets dependency Property implementation for Password
  /// </summary>
  public SecureString Password {
    get {
      return (SecureString)GetValue(PasswordProperty);
    }

    set {
      SetValue(PasswordProperty, value);
    }
  }
  #endregion

  #region Methods
  /// <summary>
  ///   Method to handle PreviewExecutedHandler events
  /// </summary>
  /// <param name="sender">Sender object</param>
  /// <param name="executedRoutedEventArgs">Event Text Arguments</param>
  private static void PreviewExecutedHandler(object sender, ExecutedRoutedEventArgs executedRoutedEventArgs) {
    if (executedRoutedEventArgs.Command == ApplicationCommands.Copy ||
        executedRoutedEventArgs.Command == ApplicationCommands.Cut ||
        executedRoutedEventArgs.Command == ApplicationCommands.Paste) {
      executedRoutedEventArgs.Handled = true;
    }
  }

  /// <summary>
  ///   Method to handle PreviewTextInput events
  /// </summary>
  /// <param name="sender">Sender object</param>
  /// <param name="textCompositionEventArgs">Event Text Arguments</param>
  private void OnPreviewTextInput(object sender, TextCompositionEventArgs textCompositionEventArgs) {
    AddToSecureString(textCompositionEventArgs.Text);
    textCompositionEventArgs.Handled = true;
  }

  /// <summary>
  ///   Method to handle PreviewKeyDown events
  /// </summary>
  /// <param name="sender">Sender object</param>
  /// <param name="keyEventArgs">Event Text Arguments</param>
  private void OnPreviewKeyDown(object sender, KeyEventArgs keyEventArgs) {
    Key pressedKey = keyEventArgs.Key == Key.System ? keyEventArgs.SystemKey : keyEventArgs.Key;
    switch (pressedKey) {
      case Key.Space:
        AddToSecureString(" ");
        keyEventArgs.Handled = true;
        break;
      case Key.Back:
      case Key.Delete:
        if (SelectionLength > 0) {
          RemoveFromSecureString(SelectionStart, SelectionLength);
        } else if (pressedKey == Key.Delete && CaretIndex < Text.Length) {
          RemoveFromSecureString(CaretIndex, 1);
        } else if (pressedKey == Key.Back && CaretIndex > 0) {
          int caretIndex = CaretIndex;
          if (CaretIndex > 0 && CaretIndex < Text.Length)
            caretIndex = caretIndex - 1;
          RemoveFromSecureString(CaretIndex - 1, 1);
          CaretIndex = caretIndex;
        }

        keyEventArgs.Handled = true;
        break;
    }
  }

  /// <summary>
  ///   Method to add new text into SecureString and process visual output
  /// </summary>
  /// <param name="text">Text to be added</param>
  private void AddToSecureString(string text) {
    if (SelectionLength > 0) {
      RemoveFromSecureString(SelectionStart, SelectionLength);
    }

    foreach (char c in text) {
      int caretIndex = CaretIndex;
      Password.InsertAt(caretIndex, c);
      MaskAllDisplayText();
      if (caretIndex == Text.Length) {
        _maskTimer.Stop();
        _maskTimer.Start();
        Text = Text.Insert(caretIndex++, c.ToString());
      } else {
        Text = Text.Insert(caretIndex++, "*");
      }
      CaretIndex = caretIndex;
    }
  }

  /// <summary>
  ///   Method to remove text from SecureString and process visual output
  /// </summary>
  /// <param name="startIndex">Start Position for Remove</param>
  /// <param name="trimLength">Length of Text to be removed</param>
  private void RemoveFromSecureString(int startIndex, int trimLength) {
    int caretIndex = CaretIndex;
    for (int i = 0; i < trimLength; ++i) {
      Password.RemoveAt(startIndex);
    }

    Text = Text.Remove(startIndex, trimLength);
    CaretIndex = caretIndex;
  }

  private void MaskAllDisplayText() {
    _maskTimer.Stop();
    int caretIndex = CaretIndex;
    Text = new string('*', Text.Length);
    CaretIndex = caretIndex;
  }
  #endregion
}

工作示例：

Download Link

您可以在控件中输入一些内容并检查其下方显示的存储值。

在这个示例中，我添加了一个 string 类型的新 DP，以显示控件工作正常。您显然不想在您的实时代码中使用该 DP (HiddenText)，但我希望该示例有助于分析该类是否确实有效:)