How to clear the contents of a PasswordBox when login fails without databinding?

Question

I have a wpf application and I am following the mvvm pattern carefully for reasons beyond my control. I do not want to databind to my PasswordBox for security reasons beyond

Answer 1

You can create your attached DependencyProperty and use it as a XAML or in code. Example:

Listing of PasswordBehaviors:

public static class PasswordBehaviors
{
    public static void SetIsClear(DependencyObject target, bool value)
    {
        target.SetValue(IsClearProperty, value);
    }

    public static readonly DependencyProperty IsClearProperty =
                                              DependencyProperty.RegisterAttached("IsClear",
                                              typeof(bool),
                                              typeof(PasswordBehaviors),
                                              new UIPropertyMetadata(false, OnIsClear));

    private static void OnIsClear(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue is bool && ((bool)e.NewValue) == true)
        {
            PasswordBox MyPasswordBox = sender as PasswordBox;

            if (MyPasswordBox != null)
            {
                MyPasswordBox.Clear();
            }
        }
    }
}

Using with EventTrigger:

    
        
            
                
                    
                        True
                    
                
            
        
    

Using with DataTrigger (in Style/DataTemplate/etc):

Using with Trigger (in Style):

Using behind code:

private void Clear_Click(object sender, RoutedEventArgs e)
{
    PasswordBehaviors.SetIsClear(MyPasswordBox, true);
}

Copmlete example:

XAML

    
        
            
                
                    
                        
                            
                                True
                            
                        
                    
                
            
        

        
            
                
                    
                        
                            
                                False
                            
                        
                    
                
            
        
    

    

    

    

Code behind

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    //private void Clear_Click(object sender, RoutedEventArgs e)
    //{
    //    PasswordBehaviors.SetIsClear(MyPasswordBox, true);
    //}

    //private void ResetClear_Click(object sender, RoutedEventArgs e)
    //{
    //    PasswordBehaviors.SetIsClear(MyPasswordBox, false);
    //}
}

public static class PasswordBehaviors
{
    public static void SetIsClear(DependencyObject target, bool value)
    {
        target.SetValue(IsClearProperty, value);
    }

    public static readonly DependencyProperty IsClearProperty =
                                              DependencyProperty.RegisterAttached("IsClear",
                                              typeof(bool),
                                              typeof(PasswordBehaviors),
                                              new UIPropertyMetadata(false, OnIsClear));

    private static void OnIsClear(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue is bool && ((bool)e.NewValue) == true)
        {
            PasswordBox MyPasswordBox = sender as PasswordBox;

            if (MyPasswordBox != null)
            {
                MyPasswordBox.Clear();
            }
        }
    }
}