[WPF]实现密码框的密码绑定

[WPF]实现密码框的密码绑定                                                 [WPF]实现密码框的密码绑定
                                                           周银辉

正如绑定TextBox控件的Text属性一样, 我们希望能够将PasswordBox空间的Password属性进行绑定, 比如在MVVM模式中,这似乎是必须的, 但可惜的是, Password属性是不支持绑定的(不是依赖属性, 也没有实现INotifyPropertyChanged).
这可能是出于安全性的考虑. 但在我们的系统为了实现View层密码框中的密码与后台其它层之间的密码属性之间的绑定, 可以采取如下思路: 将密码框的密码和某一个缓冲区进行同步, 缓冲区在和后台进行绑定. 其中密码框与缓冲区之间的同步可采用事件进行通知, 并将缓冲区打造成依赖属性, 然后缓冲区就支持绑定了, 并给后台提供正确的密码.
缓冲区可以是哈希表或其他字典结构, 以便将密码框和缓冲区中的密码一 一对应起来, 也可以使AttachProperty(附加属性), 其实附加属性的机制也就是对缓存了的一个大字典进行操作



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    public static class PasswordBoxBindingHelper
    {
        
public static bool GetIsPasswordBindingEnabled(DependencyObject obj)
        {
            
return (bool)obj.GetValue(IsPasswordBindingEnabledProperty);
        }

        
public static void SetIsPasswordBindingEnabled(DependencyObject obj, bool value)
        {
            obj.SetValue(IsPasswordBindingEnabledProperty, value);
        }

        
public static readonly DependencyProperty IsPasswordBindingEnabledProperty =
            DependencyProperty.RegisterAttached(
"IsPasswordBindingEnabled"typeof(bool), 
            
typeof(PasswordBoxBindingHelper), 
            
new UIPropertyMetadata(false, OnIsPasswordBindingEnabledChanged));

        
private static void OnIsPasswordBindingEnabledChanged(DependencyObject obj, 
                                                              DependencyPropertyChangedEventArgs e)
        {
            var passwordBox 
= obj as PasswordBox;

            
if(passwordBox != null)
            {
                passwordBox.PasswordChanged 
-= PasswordBoxPasswordChanged;

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

        
//when the passwordBox's password changed, update the buffer
        static void PasswordBoxPasswordChanged(object sender, RoutedEventArgs e)
        {
            var passwordBox 
= (PasswordBox) sender;

            
if (!String.Equals(GetBindedPassword(passwordBox),passwordBox.Password))
            {
                SetBindedPassword(passwordBox, passwordBox.Password);
            }
        }


        
public static string GetBindedPassword(DependencyObject obj)
        {
            
return (string)obj.GetValue(BindedPasswordProperty);
        }


        
public static void SetBindedPassword(DependencyObject obj, string value)
        {
            obj.SetValue(BindedPasswordProperty, value);
        }

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

        
//when the buffer changed, upate the passwordBox's password
        private static void OnBindedPasswordChanged(DependencyObject obj, 
                                                    DependencyPropertyChangedEventArgs e)
        {
            var passwordBox 
= obj as PasswordBox;
            
if (passwordBox != null)
            {

                passwordBox.Password 
= e.NewValue == null ? string.Empty : e.NewValue.ToString();
            }
        }       

    }


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<PasswordBox  Helpers:PasswordBoxBindingHelper.IsPasswordBindingEnabled="True" 
                     Helpers:PasswordBoxBindingHelper.BindedPassword
=
                     "
{Binding Path=Password, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />


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        private static void SetPasswordBoxSelection(PasswordBox passwordBox, int start, int length)
        {
            var select 
= passwordBox.GetType().GetMethod("Select"
                            BindingFlags.Instance 
| BindingFlags.NonPublic);

            select.Invoke(passwordBox, 
new object[] { start, length });
        }

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