WPF PasswordBox的数据绑定功能处理

当我们输入的敏感信息时，用到最多的就是使用PasswordBox。但是由于某些原因或考虑，wpf的标准并不支持Binding方法。PasswordBox的属性只是一个普通的CLR属性，并不是Dependency 属性。

幸运的是，wpf具有附加属性的概念，允许我们更加容易的进行控件的扩展。下面就使用附加属性进行处理PasswordBox的绑定功能

使用方法如下

设定BindPassword属性为True，这样代码就会在PasswordBox上侦听PasswordChanged事件，只要当PasswordBox的内容有更改，代码就会把更改的新的值推送到附加属性：BoundPassword中，然后把要绑定的值绑定到BoundPassword中。唯一复杂的就是要确保整个事件不会递归和UpdatingPassword私有属性

using System.Windows;
using System.Windows.Controls;
 
namespace FunctionalFun.UI
{
  public static class PasswordBoxAssistant
  {
      public static readonly DependencyProperty BoundPassword =
          DependencyProperty.RegisterAttached("BoundPassword", typeof(string), typeof(PasswordBoxAssistant), new PropertyMetadata(string.Empty, OnBoundPasswordChanged));
 
      public static readonly DependencyProperty BindPassword = DependencyProperty.RegisterAttached(
          "BindPassword", typeof (bool), typeof (PasswordBoxAssistant), new PropertyMetadata(false, OnBindPasswordChanged));
 
      private static readonly DependencyProperty UpdatingPassword =
          DependencyProperty.RegisterAttached("UpdatingPassword", typeof(bool), typeof(PasswordBoxAssistant), new PropertyMetadata(false));
 
      private static void OnBoundPasswordChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
      {
          PasswordBox box = d as PasswordBox;
 
          // only handle this event when the property is attached to a PasswordBox
          // and when the BindPassword attached property has been set to true
          if (d == null || !GetBindPassword(d))
          {
              return;
          }
 
          // avoid recursive updating by ignoring the box's changed event
          box.PasswordChanged -= HandlePasswordChanged;
 
          string newPassword = (string)e.NewValue;
 
          if (!GetUpdatingPassword(box))
          {
              box.Password = newPassword;
          }
 
          box.PasswordChanged += HandlePasswordChanged;
      }
 
      private static void OnBindPasswordChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
      {
          // when the BindPassword attached property is set on a PasswordBox,
          // start listening to its PasswordChanged event
 
          PasswordBox box = dp as PasswordBox;
 
          if (box == null)
          {
              return;
          }
 
          bool wasBound = (bool)(e.OldValue);
          bool needToBind = (bool)(e.NewValue);
 
          if (wasBound)
          {
              box.PasswordChanged -= HandlePasswordChanged;
          }
 
          if (needToBind)
          {
              box.PasswordChanged += HandlePasswordChanged;
          }
      }
 
      private static void HandlePasswordChanged(object sender, RoutedEventArgs e)
      {
          PasswordBox box = sender as PasswordBox;
 
          // set a flag to indicate that we're updating the password
          SetUpdatingPassword(box, true);
          // push the new password into the BoundPassword property
          SetBoundPassword(box, box.Password);
          SetUpdatingPassword(box, false);
      }
 
      public static void SetBindPassword(DependencyObject dp, bool value)
      {
          dp.SetValue(BindPassword, value);
      }
 
      public static bool GetBindPassword(DependencyObject dp)
      {
          return (bool)dp.GetValue(BindPassword);
      }
 
      public static string GetBoundPassword(DependencyObject dp)
      {
          return (string)dp.GetValue(BoundPassword);
      }
 
      public static void SetBoundPassword(DependencyObject dp, string value)
      {
          dp.SetValue(BoundPassword, value);
      }
 
      private static bool GetUpdatingPassword(DependencyObject dp)
      {
          return (bool)dp.GetValue(UpdatingPassword);
      }
 
      private static void SetUpdatingPassword(DependencyObject dp, bool value)
      {
          dp.SetValue(UpdatingPassword, value);
      }
  }
}

原文 

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