WPF中无法绑定PasswordBox的Password问题

由于PasswordBox的Password不是依赖属性，所以无法对其进行绑定。

这是需要通过添加附加属性，在附加属性中通过PasswordBox中可以用的依赖属性关联，实现Password绑定。

依赖属性：

-----MonitorPassword：关联PasswordBox中的PasswordChange事件。当PasswordChange事件发生时，修改AttachPassword属性。

-----AttachPassword：被绑定的附加属性

-----HasText：是否显示水印附加属性

附加属性类：

public class PasswordProperties
{
    #region 绑定PasswordBox.PasswordChange事件，一旦发生passwordChange事件，设置其余两个附件属性；
    public static bool GetMonitorPassword(DependencyObject obj)
    {
        return (bool)obj.GetValue(MonitorPasswordProperty);
    }
 
    public static void SetMonitorPassword(DependencyObject obj, bool value)
    {
        obj.SetValue(MonitorPasswordProperty, value);
    }
 
    // Using a DependencyProperty as the backing store for MonitorPassword.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty MonitorPasswordProperty =
        DependencyProperty.RegisterAttached("MonitorPassword", typeof(bool), typeof(PasswordProperties), new PropertyMetadata(false, OnMonitorPasswordChanged));
 
    private static void OnMonitorPasswordChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        PasswordBox? p = d as PasswordBox;
 
        if (p == null) return;
 
        p.PasswordChanged -= P_PasswordChanged;
 
        if ((bool)e.NewValue)
        {
            SetHasText(p);
            p.PasswordChanged += P_PasswordChanged;
        }
    }
    private static void P_PasswordChanged(object sender, RoutedEventArgs e)
    {
        PasswordBox? p = sender as PasswordBox;
        if(p == null) return;
 
        SetHasText(p);
        SetAttachPassword(p);
    }
    #endregion
 
    #region password的附件属性
    public static string GetAttachPassword(PasswordBox obj)
    {
        return (string)obj.GetValue(AttachPasswordProperty);
    }
 
    public static void SetAttachPassword(PasswordBox obj)
    {
        obj.SetValue(AttachPasswordProperty, obj.Password);
    }
 
    // Using a DependencyProperty as the backing store for AttachPassword.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty AttachPasswordProperty =
        DependencyProperty.RegisterAttached("AttachPassword", typeof(string), typeof(PasswordProperties), new PropertyMetadata(0));
    #endregion
 
    #region password是否为空的附件属性，用于判断是否显示水印
    public static bool GetHasText(PasswordBox obj)
    {
        return (bool)obj.GetValue(HasTextProperty);
    }
 
    public static void SetHasText(PasswordBox obj)
    {
        obj.SetValue(HasTextProperty, obj.Password.Length > 0);
    }
 
    // Using a DependencyProperty as the backing store for HasText.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty HasTextProperty =
        DependencyProperty.RegisterAttached("HasText", typeof(bool), typeof(PasswordProperties), new PropertyMetadata(false));
    #endregion
}