wpf关于PasswordBox的绑定Password的问题（MVVM框架）

当尝试数据绑定一个PasswordBox的密码属性，你会认识到，你不能做数据就可以了绑定。 这样做的原因是，该密码属性不是由DependencyProperty支持。

原因是数据绑定密码是不是一个好的设计，出于安全考虑，应该避免。 但有时这种安全是没有必要的，那么它不但麻烦，你不能绑定到Password属性。 在这种特殊情况下，你可以利用以下PasswordBoxBindingHelper的。

 <PasswordBox Name="pwdBoxPWD" 
                     tools:PasswordBoxBindingHelper.IsPasswordBindingEnabled="True" 
                     tools:PasswordBoxBindingHelper.BindedPassword= "{Binding Path=Password, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"  
                     HorizontalAlignment="Left"
                     Height="38" Margin="167,170,0,0"  PasswordChar="*" VerticalAlignment="Top" Width="258" FontSize="24" VerticalContentAlignment="Center" MaxLength="18" />

PasswordBoxBindingHelper通过调用PasswordBoxBindingHelper.BindedPasswordProperty附着到passwordbox。附加属性PasswordBoxBindingHelper.Password提供了PasswordBox控制的原始密码属性的拷贝PassWord用于绑定。

 public static class PasswordBoxBindingHelper
    {
        //BindedPassword
        public static readonly DependencyProperty BindedPasswordProperty =
            DependencyProperty.RegisterAttached("BindedPassword",
            typeof(string), typeof(PasswordBoxBindingHelper),
            new FrameworkPropertyMetadata(string.Empty, OnBindedPasswordChanged));

        public static string GetBindedPassword(DependencyObject dp)
        {
            return (string)dp.GetValue(BindedPasswordProperty);
        }
        public static void SetBindedPassword(DependencyObject dp, string value)
        {
            dp.SetValue(BindedPasswordProperty, value);
        }

        private static void OnBindedPasswordChanged(DependencyObject sender,
          DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            if (passwordBox == null)
            {
                return;
            }
            passwordBox.PasswordChanged -= PasswordChanged;

            if (!(bool)GetIsUpdating(passwordBox))
            {
                passwordBox.Password = (string)e.NewValue;
            }
            passwordBox.PasswordChanged += PasswordChanged;
        }


        //IsPasswordBindingEnabled
        public static readonly DependencyProperty IsPasswordBindingEnabledProperty =
            DependencyProperty.RegisterAttached("IsPasswordBindingEnabled",
            typeof(bool), typeof(PasswordBoxBindingHelper), new PropertyMetadata(false, IsPasswordBindingEnabled));
        public static void SetIsPasswordBindingEnabled(DependencyObject dp, bool value)
        {
            dp.SetValue(IsPasswordBindingEnabledProperty, value);
        }

        public static bool GetIsPasswordBindingEnabled(DependencyObject dp)
        {
            return (bool)dp.GetValue(IsPasswordBindingEnabledProperty);
        }
        private static void IsPasswordBindingEnabled(DependencyObject sender,
           DependencyPropertyChangedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;

            if (passwordBox == null)
                return;

            if ((bool)e.OldValue)
            {
                passwordBox.PasswordChanged -= PasswordChanged;
            }

            if ((bool)e.NewValue)
            {
                passwordBox.PasswordChanged += PasswordChanged;
            }
        }

        //IsUpdating
        private static readonly DependencyProperty IsUpdatingProperty =
           DependencyProperty.RegisterAttached("IsUpdating", typeof(bool),
           typeof(PasswordBoxBindingHelper));

        private static bool GetIsUpdating(DependencyObject dp)
        {
            return (bool)dp.GetValue(IsUpdatingProperty);
        }

        private static void SetIsUpdating(DependencyObject dp, bool value)
        {
            dp.SetValue(IsUpdatingProperty, value);
        }

        private static void PasswordChanged(object sender, RoutedEventArgs e)
        {
            PasswordBox passwordBox = sender as PasswordBox;
            SetIsUpdating(passwordBox, true);
            SetBindedPassword(passwordBox, passwordBox.Password);
            SetIsUpdating(passwordBox, false);
        }
    }
}