It was necessary to implement password box with "show password" check box which shows the original password.

This article WPF PasswordBox Control is a good place to start. I've used the PasswordHelper class from the article.

The PasswordHelper is attached to the password box by calling the PasswordHelper.Attach property. The attached property PasswordHelper.Password provides a bindable copy of the original password property of the PasswordBox control.

Here is the code for the class:

public static class PasswordHelper
{
    public static readonly DependencyProperty PasswordProperty =
        DependencyProperty.RegisterAttached("Password",
        typeof(string), typeof(PasswordHelper),
        new FrameworkPropertyMetadata(string.Empty, OnPasswordPropertyChanged));

    public static readonly DependencyProperty AttachProperty =
        DependencyProperty.RegisterAttached("Attach",
        typeof(bool), typeof(PasswordHelper), new PropertyMetadata(false, Attach));

    private static readonly DependencyProperty IsUpdatingProperty =
       DependencyProperty.RegisterAttached("IsUpdating", typeof(bool), 
       typeof(PasswordHelper));


    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);
    }
}

Here is the main window XAML. Don't forget to reference the namespace of PasswordHelper class (in my case: xmlns:w="clr-namespace:TestWpfApp").

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="Auto" />
        <ColumnDefinition Width="*" />
        <ColumnDefinition Width="Auto" />
    </Grid.ColumnDefinitions>

    <TextBlock Text="Password:" />

    <PasswordBox x:Name="passwordBox"
             Grid.Column="1"
                 w:PasswordHelper.Attach="True"
                 w:PasswordHelper.Password="{Binding Text, ElementName=textBox, Mode=TwoWay}">
        <PasswordBox.Style>
            <Style TargetType="{x:Type PasswordBox}">
                <Setter Property="Visibility" Value="Visible" />
                <Style.Triggers>
                    <DataTrigger Binding="{Binding IsChecked, ElementName=showPassCheckBox}" Value="True">
                        <Setter Property="Visibility" Value="Collapsed" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </PasswordBox.Style>
    </PasswordBox>

    <TextBox x:Name="textBox"
         Grid.Column="1">
        <TextBox.Style>
            <Style TargetType="{x:Type TextBox}">
                <Setter Property="Visibility" Value="Visible" />
                <Style.Triggers>
                    <DataTrigger Binding="{Binding IsChecked, ElementName=showPassCheckBox}" Value="False">
                        <Setter Property="Visibility" Value="Collapsed" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </TextBox.Style>
    </TextBox>

    <CheckBox x:Name="showPassCheckBox" Grid.Column="2" Content="Show password" />
</Grid>

Result:

Tags: Attached Behavior PasswordBox TextBox wpf