将SecurePassword绑定到ViewModel

创建附加属性

public static class PasswordBoxAssistant
{
 public static readonly DependencyProperty BoundPassword =
      DependencyProperty.RegisterAttached("BoundPassword", typeof(string), typeof(PasswordBoxAssistant), new PropertyMetadata(string.Empty, OnBoundPasswordChanged));
  public static readonly DependencyProperty BindPassword = DependencyProperty.RegisterAttached(
      "BindPassword", typeof (bool), typeof (PasswordBoxAssistant), new PropertyMetadata(false, OnBindPasswordChanged));

  private static readonly DependencyProperty UpdatingPassword =
      DependencyProperty.RegisterAttached("UpdatingPassword", typeof(bool), typeof(PasswordBoxAssistant), new PropertyMetadata(false));
  private static void OnBoundPasswordChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
  {
      PasswordBox box = d as PasswordBox;
      // only handle this event when the property is attached to a PasswordBox
      // and when the BindPassword attached property has been set to true
      if (d == null || !GetBindPassword(d))
      {
          return;
      }
      // avoid recursive updating by ignoring the box's changed event
      box.PasswordChanged -= HandlePasswordChanged;
      string newPassword = (string)e.NewValue;
      if (!GetUpdatingPassword(box))
      {
          box.Password = newPassword;
      }
      box.PasswordChanged += HandlePasswordChanged;
  }
  private static void OnBindPasswordChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
  {
      // when the BindPassword attached property is set on a PasswordBox,
      // start listening to its PasswordChanged event
      PasswordBox box = dp as PasswordBox;
      if (box == null)
      {
          return;
      }
      bool wasBound = (bool)(e.OldValue);
      bool needToBind = (bool)(e.NewValue);
      if (wasBound)
      {
          box.PasswordChanged -= HandlePasswordChanged;
      }
      if (needToBind)
      {
          box.PasswordChanged += HandlePasswordChanged;
      }
  }
  private static void HandlePasswordChanged(object sender, RoutedEventArgs e)
  {
      PasswordBox box = sender as PasswordBox;
      // set a flag to indicate that we're updating the password
      SetUpdatingPassword(box, true);
      // push the new password into the BoundPassword property
      SetBoundPassword(box, box.Password);
      SetUpdatingPassword(box, false);
  }
  public static void SetBindPassword(DependencyObject dp, bool value)
  {
      dp.SetValue(BindPassword, value);
  }
  public static bool GetBindPassword(DependencyObject dp)
  {
      return (bool)dp.GetValue(BindPassword);
  }
  public static string GetBoundPassword(DependencyObject dp)
  {
      return (string)dp.GetValue(BoundPassword);
  }
  public static void SetBoundPassword(DependencyObject dp, string value)
  {
      dp.SetValue(BoundPassword, value);
  }
  private static bool GetUpdatingPassword(DependencyObject dp)
  {
      return (bool)dp.GetValue(UpdatingPassword);
  }
  private static void SetUpdatingPassword(DependencyObject dp, bool value)
  {
      dp.SetValue(UpdatingPassword, value);
  }
}

在您的XAML 中

<Page xmlns:ff="clr-namespace:FunctionalFun.UI">
<!-- [Snip] -->
  <PasswordBox x:Name="PasswordBox"
      ff:PasswordBoxAssistant.BindPassword="true"  ff:PasswordBoxAssistant.BoundPassword="{Binding Path=Password, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
</Page>

你可能无论如何都不想这样做，但如果你真的想继续的话。

WPF/Silverlight PasswordBox不公开Password属性的DP的原因与安全性有关。如果WPF/Silverlight要为Password保留DP，则需要框架在内存中保持密码本身未加密。这被认为是一个相当麻烦的安全攻击向量。PasswordBox使用加密内存，访问密码的唯一方法是通过CLR属性。

我建议在访问PasswordBox.Password CLR属性时，不要将其放在任何变量中或作为任何属性的值。在客户端机器RAM上以明文形式保存密码是一个安全问题。

SecurePassword无法使用绑定完成。

.NET文档首先解释了为什么PasswordBox不可绑定。

另一种解决方案是将PasswordBox放在ViewModel公共类LoginViewModel 中

public class LoginViewModel
{
   // other properties here
   public PasswordBox Password
   {
      get { return m_passwordBox; }
   }
   // Executed when the Login button is clicked.
   private void LoginExecute()
   {
      var password = Password.SecurePassword;
      // do more stuff...
   }
}

是的，您违反了ViewModel的最佳实践，但是

1. 最佳实践是"在大多数情况下行之有效的建议"而不是严格的规则和
2. 编写简单、易读、可维护的代码并避免不必要的复杂性也是"最佳实践"规则之一（"附带财产"可能会稍微违反变通方法）

我觉得我找到了一个有点奇怪的解决方案。如果有需要改进的地方，请改进：）

我只是把它改成这样：

Behavior:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using System.Windows.Interactivity;
using System.Security;
namespace Knerd.Behaviors {
    public class PasswordChangedBehavior : Behavior<PasswordBox> {
        protected override void OnAttached() {
            AssociatedObject.PasswordChanged += AssociatedObject_PasswordChanged;
            base.OnAttached();
        }
        private void AssociatedObject_PasswordChanged(object sender, RoutedEventArgs e) {
            if (AssociatedObject.SecurePassword != null)
                AssociatedObject.DataContext = AssociatedObject.SecurePassword.Copy();
        }
        protected override void OnDetaching() {
            AssociatedObject.PasswordChanged -= AssociatedObject_PasswordChanged;
            base.OnDetaching();
        }
        // Using a DependencyProperty as the backing store for TargetPassword.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty TargetPasswordProperty = DependencyProperty.Register("TargetPassword", typeof(SecureString), typeof(PasswordChangedBehavior), new PropertyMetadata(default(SecureString)));
    }
}

ViewModel根本没有改变，但这是我的View:

<PasswordBox Grid.Column="1" Grid.Row="1" Margin="5" Width="300" MinWidth="200" DataContext="{Binding Password, Mode=TwoWay}">
    <i:Interaction.Behaviors>
        <behaviors:PasswordChangedBehavior />
    </i:Interaction.Behaviors>
</PasswordBox>

这样做非常完美，不会暴露明文密码。