【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>