基于WPF系统框架设计(8)-PasswordBox传值到ViewMode

应用场景

我要做一个系统登录功能，需要传用户名和密码到ViewModel中，可是PasswordBox传值到ViewModel中好像跟TextBox等控件不一样。这里需要用到附加属性。

附加属性：一个属性本来不属于某个对象，但是由于某种需求而被后来附加上，即把对象放入一个特定的环境后才具有的属性。 作用就是将属性与数据类型（宿主）解耦，让数据类型设计更加灵活。

本质还是依赖属性，二者仅在包装器和注册上有点区别。

实现步骤

现在我写了个附加属性类，如下：

（1）针对PasswordBox写一个帮助类(PasswordBoxHelper)，如下：

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Windows;

using System.Windows.Controls;



namespace TLAgent.SecurityManager.WPF

{

    /// <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);

        }

    }  

}

（2）给这个PasswordBox添加附加属性,如下绑定：

<PasswordBox x:Name="txtPassword" Height="23" Helper:PasswordBoxHelper.Attach="True" Helper:PasswordBoxHelper.Password="{Binding Path=AuthUser.Password,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="101,92,0,0"  VerticalAlignment="Top" Width="178" TabIndex="2">

            <i:Interaction.Triggers>

                <i:EventTrigger EventName="KeyDown">

                    <Helper:InteractiveCommand Command="{Binding EnterLoginCommand}" CommandName="EnterLoginCommand" CommandParameter="{Binding ElementName=txtUserName}"/>

                </i:EventTrigger>

            </i:Interaction.Triggers>

        </PasswordBox>

如此简单，这样就解决了。