一个不违反MVVM模式的简单解决方案是在ViewModel中引入一个获取密码的事件(或委托)。

在ViewModel中:

public event eventandler <HarvestPasswordEventArgs> HarvestPassword;

使用这些EventArgs:

class HarvestPasswordEventArgs : EventArgs
{
    public string Password;
}

在View中，订阅创建ViewModel时的事件，并填写密码值。

_viewModel.HarvestPassword += (sender, args) => 
    args.Password = passwordBox1.Password;

在ViewModel中，当你需要密码时，你可以触发事件并从那里获取密码:

if (HarvestPassword == null)
  //bah 
  return;

var pwargs = new HarvestPasswordEventArgs();
HarvestPassword(this, pwargs);

LoginHelpers.Login(Username, pwargs.Password);

您可以在WPF应用程序框架(WAF)项目的ViewModel样例应用程序中找到PasswordBox的解决方案。

然而，犹斯丁是对的。不要在View和ViewModel之间以纯文本的形式传递密码。请使用SecureString代替(参见MSDN PasswordBox)。

为了在不破坏MVVM的情况下解决OP问题，我将使用自定义值转换器和必须从密码框中检索的值(密码)的包装器。

public interface IWrappedParameter<T>
{
    T Value { get; }
}

public class PasswordBoxWrapper : IWrappedParameter<string>
{
    private readonly PasswordBox _source;

    public string Value
    {
        get { return _source != null ? _source.Password : string.Empty; }
    }

    public PasswordBoxWrapper(PasswordBox source)
    {
        _source = source;
    }
}

public class PasswordBoxConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        // Implement type and value check here...
        return new PasswordBoxWrapper((PasswordBox)value);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new InvalidOperationException("No conversion.");
    }
}

在视图模型中:

public string Username { get; set; }

public ICommand LoginCommand
{
    get
    {
        return new RelayCommand<IWrappedParameter<string>>(password => { Login(Username, password); });
    }
}

private void Login(string username, string password)
{
    // Perform login here...
}

因为视图模型使用IWrappedParameter<T>，所以它不需要任何关于PasswordBoxWrapper或PasswordBoxConverter的知识。这样您就可以将PasswordBox对象与视图模型隔离开来，并且不会破坏MVVM模式。

在视图中:

<Window.Resources>
    <h:PasswordBoxConverter x:Key="PwdConverter" />
</Window.Resources>
...
<PasswordBox Name="PwdBox" />
<Button Content="Login" Command="{Binding LoginCommand}"
        CommandParameter="{Binding ElementName=PwdBox, Converter={StaticResource PwdConverter}}" />

以下是我的看法:

Using an attached property to bind the password defeats the purpose of securing the password. The Password property of a password box is not bindable for a reason. Passing the password box as command parameter will make the ViewModel aware of the control. This will not work if you plan to make your ViewModel reusable cross platform. Don't make your VM aware of your View or any other controls. I don't think introducing a new property, an interface, subscribing to password changed events or any other complicated things is necessary for a simple task of providing the password.

XAML

<PasswordBox x:Name="pbPassword" />
<Button Content="Login" Command="{Binding LoginCommand}" x:Name="btnLogin"/>

代码背后——使用代码背后并不一定违反MVVM。只要你不把任何业务逻辑放在里面。

btnLogin.CommandParameter = new Func<string>(()=>pbPassword.Password); 

ViewModel

LoginCommand = new RelayCommand<Func<string>>(getpwd=> { service.Login(username, getpwd()); });

我花了大量时间研究各种解决方案。我不喜欢装饰器的想法，行为弄乱了验证UI，背后的代码……真的吗?

最好的方法是坚持自定义附加属性，并绑定到视图模型中的SecureString属性。尽量把它放在里面。当你需要快速访问纯密码时，使用下面的代码将其临时转换为不安全的字符串:

namespace Namespace.Extensions
{
    using System;
    using System.Runtime.InteropServices;
    using System.Security;

    /// <summary>
    /// Provides unsafe temporary operations on secured strings.
    /// </summary>
    [SuppressUnmanagedCodeSecurity]
    public static class SecureStringExtensions
    {
        /// <summary>
        /// Converts a secured string to an unsecured string.
        /// </summary>
        public static string ToUnsecuredString(this SecureString secureString)
        {
            // copy&paste from the internal System.Net.UnsafeNclNativeMethods
            IntPtr bstrPtr = IntPtr.Zero;
            if (secureString != null)
            {
                if (secureString.Length != 0)
                {
                    try
                    {
                        bstrPtr = Marshal.SecureStringToBSTR(secureString);
                        return Marshal.PtrToStringBSTR(bstrPtr);
                    }
                    finally
                    {
                        if (bstrPtr != IntPtr.Zero)
                            Marshal.ZeroFreeBSTR(bstrPtr);
                    }
                }
            }
            return string.Empty;
        }

        /// <summary>
        /// Copies the existing instance of a secure string into the destination, clearing the destination beforehand.
        /// </summary>
        public static void CopyInto(this SecureString source, SecureString destination)
        {
            destination.Clear();
            foreach (var chr in source.ToUnsecuredString())
            {
                destination.AppendChar(chr);
            }
        }

        /// <summary>
        /// Converts an unsecured string to a secured string.
        /// </summary>
        public static SecureString ToSecuredString(this string plainString)
        {
            if (string.IsNullOrEmpty(plainString))
            {
                return new SecureString();
            }

            SecureString secure = new SecureString();
            foreach (char c in plainString)
            {
                secure.AppendChar(c);
            }
            return secure;
        }
    }
}

确保允许GC收集UI元素，因此不要为PasswordBox上的PasswordChanged事件使用静态事件处理程序。 我还发现了一个异常，当使用SecurePassword属性设置它时，控件没有更新UI，这就是为什么我将密码复制到password的原因。

namespace Namespace.Controls
{
    using System.Security;
    using System.Windows;
    using System.Windows.Controls;
    using Namespace.Extensions;

    /// <summary>
    /// Creates a bindable attached property for the <see cref="PasswordBox.SecurePassword"/> property.
    /// </summary>
    public static class PasswordBoxHelper
    {
        // an attached behavior won't work due to view model validation not picking up the right control to adorn
        public static readonly DependencyProperty SecurePasswordBindingProperty = DependencyProperty.RegisterAttached(
            "SecurePassword",
            typeof(SecureString),
            typeof(PasswordBoxHelper),
            new FrameworkPropertyMetadata(new SecureString(),FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, AttachedPropertyValueChanged)
        );

        private static readonly DependencyProperty _passwordBindingMarshallerProperty = DependencyProperty.RegisterAttached(
            "PasswordBindingMarshaller",
            typeof(PasswordBindingMarshaller),
            typeof(PasswordBoxHelper),
            new PropertyMetadata()
        );

        public static void SetSecurePassword(PasswordBox element, SecureString secureString)
        {
            element.SetValue(SecurePasswordBindingProperty, secureString);
        }

        public static SecureString GetSecurePassword(PasswordBox element)
        {
            return element.GetValue(SecurePasswordBindingProperty) as SecureString;
        }

        private static void AttachedPropertyValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            // we'll need to hook up to one of the element's events
            // in order to allow the GC to collect the control, we'll wrap the event handler inside an object living in an attached property
            // don't be tempted to use the Unloaded event as that will be fired  even when the control is still alive and well (e.g. switching tabs in a tab control) 
            var passwordBox = (PasswordBox)d;
            var bindingMarshaller = passwordBox.GetValue(_passwordBindingMarshallerProperty) as PasswordBindingMarshaller;
            if (bindingMarshaller == null)
            {
                bindingMarshaller = new PasswordBindingMarshaller(passwordBox);
                passwordBox.SetValue(_passwordBindingMarshallerProperty, bindingMarshaller);
            }

            bindingMarshaller.UpdatePasswordBox(e.NewValue as SecureString);
        }

        /// <summary>
        /// Encapsulated event logic
        /// </summary>
        private class PasswordBindingMarshaller
        {
            private readonly PasswordBox _passwordBox;
            private bool _isMarshalling;

            public PasswordBindingMarshaller(PasswordBox passwordBox)
            {
                _passwordBox = passwordBox;
                _passwordBox.PasswordChanged += this.PasswordBoxPasswordChanged;
            }

            public void UpdatePasswordBox(SecureString newPassword)
            {
                if (_isMarshalling)
                {
                    return;
                }

                _isMarshalling = true;
                try
                {
                    // setting up the SecuredPassword won't trigger a visual update so we'll have to use the Password property
                    _passwordBox.Password = newPassword.ToUnsecuredString();

                    // you may try the statement below, however the benefits are minimal security wise (you still have to extract the unsecured password for copying)
                    //newPassword.CopyInto(_passwordBox.SecurePassword);
                }
                finally
                {
                    _isMarshalling = false;
                }
            }

            private void PasswordBoxPasswordChanged(object sender, RoutedEventArgs e)
            {
                // copy the password into the attached property
                if (_isMarshalling)
                {
                    return;
                }

                _isMarshalling = true;
                try
                {
                    SetSecurePassword(_passwordBox, _passwordBox.SecurePassword.Copy());
                }
                finally
                {
                    _isMarshalling = false;
                }
            }
        }
    }
}

以及XAML用法:

<PasswordBox controls:PasswordBoxHelper.SecurePassword="{Binding LogonPassword, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True}">

我在视图模型中的属性是这样的:

[RequiredSecureString]
public SecureString LogonPassword
{
   get
   {
       return _logonPassword;
   }
   set
   {
       _logonPassword = value;
       NotifyPropertyChanged(nameof(LogonPassword));
   }
}

RequiredSecureString只是一个简单的自定义验证器，它有以下逻辑:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = true)]    
public class RequiredSecureStringAttribute:ValidationAttribute
{
    public RequiredSecureStringAttribute()
        :base("Field is required")
    {            
    }

    public override bool IsValid(object value)
    {
        return (value as SecureString)?.Length > 0;
    }
}

给你。一个完整的和经过测试的纯MVVM解决方案。

对不起，你做错了。

人们应该在眼皮内侧纹以下安全指南: 永远不要在记忆中保存纯文本密码。

WPF/Silverlight PasswordBox不为Password属性公开DP的原因与安全有关。 如果WPF/Silverlight要为密码保留一个DP，那么就需要框架在内存中保持密码本身不加密。这被认为是一个相当麻烦的安全攻击载体。 PasswordBox使用加密内存(某种程度上)，访问密码的唯一方法是通过CLR属性。

我建议访问密码框时。密码CLR属性，您将避免将它放在任何变量或作为任何属性的值。 在客户端机器RAM中以明文形式保存密码是一个安全禁忌。 所以去掉公共字符串Password {get;设置;你已经站在那里了。

访问PasswordBox时。密码，把它拿出来，尽快发到服务器上。 不要保留密码的值，也不要像对待任何其他客户端机器文本一样对待它。不要在记忆中保存清晰的文本密码。

我知道这打破了MVVM模式，但您不应该绑定到PasswordBox。密码附加DP，存储您的密码在ViewModel或任何其他类似的诡计。

如果你正在寻找一个过度架构的解决方案，这里有一个: 1. 使用一个方法创建IHavePassword接口，该方法返回密码明文。 2. 让你的UserControl实现一个IHavePassword接口。 3.注册UserControl实例到你的IoC实现IHavePassword接口。 4. 当服务器请求您的密码发生时，调用IoC实现IHavePassword，只会得到梦寐以求的密码。

这只是我的看法。

——贾斯汀