【转】WPF中PasswordBox控件的Password属性的数据绑定

英文原文：http://www.wpftutorial.net/PasswordBox.html

中文原文：http://blog.csdn.net/oyi319/article/details/6551532

WPF的PasswordBox控件的Password属性不是依赖属性，无法直接进行数据绑定，为使其在MVVM模式中正常使用，可以为PasswordBox增加一个助手类，代码如下：

注：代码摘自：http://www.wpftutorial.net/PasswordBox.html

 using System.Windows;
 using System.Windows.Controls;
 namespace Oyi319.Helper
 {
     /// <summary>
     /// 为PasswordBox控件的Password增加绑定功能
     /// </summary>
     public static class PasswordBoxHelper
     {
         public static readonly DependencyProperty PasswordProperty =
             DependencyProperty.RegisterAttached("Password",
             typeof(string), typeof(PasswordBoxHelper),
             new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));
         public static readonly DependencyProperty AttachProperty =
             DependencyProperty.RegisterAttached("Attach",
             typeof(bool), typeof(PasswordBoxHelper), new PropertyMetadata(false, Attach));
         private static readonly DependencyProperty IsUpdatingProperty =
            DependencyProperty.RegisterAttached("IsUpdating", typeof(bool),
            typeof(PasswordBoxHelper));

         public static void SetAttach(DependencyObject dp, bool value)
         {
             dp.SetValue(AttachProperty, value);
         }
         public static bool GetAttach(DependencyObject dp)
         {
             return (bool)dp.GetValue(AttachProperty);
         }
         public static string GetPassword(DependencyObject dp)
         {
             return (string)dp.GetValue(PasswordProperty);
         }
         public static void SetPassword(DependencyObject dp, string value)
         {
             dp.SetValue(PasswordProperty, value);
         }
         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 OnPasswordPropertyChanged(DependencyObject sender,
             DependencyPropertyChangedEventArgs e)
         {
             PasswordBox passwordBox = sender as PasswordBox;
             passwordBox.PasswordChanged -= PasswordChanged;
             if (!(bool)GetIsUpdating(passwordBox))
             {
                 passwordBox.Password = (string)e.NewValue;
             }
             passwordBox.PasswordChanged += PasswordChanged;
         }
         private static void Attach(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;
             }
         }
         private static void PasswordChanged(object sender, RoutedEventArgs e)
         {
             PasswordBox passwordBox = sender as PasswordBox;
             SetIsUpdating(passwordBox, true);
             SetPassword(passwordBox, passwordBox.Password);
             SetIsUpdating(passwordBox, false);
         }
     }
 }

那么XAML绑定代码如下：

 <PasswordBox Helper:PasswordBoxHelper.Attach="True" Helper:PasswordBoxHelper.Password="{Binding Path=Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" />

MVVM模式XAML窗口声明代码如下：

 <Window
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:Helper="clr-namespace:Oyi319.Helper"
     xmlns:ViewModels="clr-namespace:Oyi319.ViewModels"
     x:Class="Oyi319.Views.Login"
     x:Name="Window"
     Title="Login"
     FocusManager.FocusedElement="{Binding ElementName=txt_UserName}" >
     <Window.DataContext>
         <ViewModels:LoginViewModel />
     </Window.DataContext>
 </Window>