DataBinding on properties with no setter

Question

How can I bind data to a property with only a getter and no setter to access it from view model in wpf? I am working with PasswordBox and want to bind its SecureString property to a ViewModel property. How can I do that?

Answer 1

I use this class and the System.Windows.Interactivity library to get access for properties with no setter:

public sealed class PropertyManager : TriggerAction<FrameworkElement>
{
    #region Fields

    private bool _bindingUpdating;
    private PropertyInfo _currentProperty;
    private bool _propertyUpdating;

    #endregion

    #region Dependency properties

    /// <summary>
    ///     Identifies the <see cref="Binding" /> dependency property.
    /// </summary>
    public static readonly DependencyProperty BindingProperty =
        DependencyProperty.Register("Binding", typeof(object), typeof(PropertyManager),
            new PropertyMetadata((o, args) =>
            {
                var propertyManager = o as PropertyManager;
                if (propertyManager == null ||
                    args.OldValue == args.NewValue) return;
                propertyManager.TrySetProperty(args.NewValue);
            }));

    /// <summary>
    ///     Identifies the <see cref="SourceProperty" /> dependency property.
    /// </summary>
    public static readonly DependencyProperty SourcePropertyProperty =
        DependencyProperty.Register("SourceProperty", typeof(string), typeof(PropertyManager),
            new PropertyMetadata(default(string)));

    /// <summary>
    ///     Binding for property <see cref="SourceProperty" />.
    /// </summary>
    public object Binding
    {
        get { return GetValue(BindingProperty); }
        set { SetValue(BindingProperty, value); }
    }

    /// <summary>
    ///     Name property to bind.
    /// </summary>
    public string SourceProperty
    {
        get { return (string)GetValue(SourcePropertyProperty); }
        set { SetValue(SourcePropertyProperty, value); }
    }

    #endregion

    #region Methods

    /// <summary>
    ///     Invokes the action.
    /// </summary>
    /// <param name="parameter">
    ///     The parameter to the action. If the action does not require a parameter, the parameter may be
    ///     set to a null reference.
    /// </param>
    protected override void Invoke(object parameter)
    {
        TrySetBinding();
    }

    /// <summary>
    ///     Tries to set binding value.
    /// </summary>
    private void TrySetBinding()
    {
        if (_propertyUpdating) return;
        PropertyInfo propertyInfo = GetPropertyInfo();
        if (propertyInfo == null) return;
        if (!propertyInfo.CanRead)
            return;
        _bindingUpdating = true;
        try
        {
            Binding = propertyInfo.GetValue(AssociatedObject, null);
        }
        finally
        {
            _bindingUpdating = false;
        }
    }

    /// <summary>
    ///     Tries to set property value.
    /// </summary>
    private void TrySetProperty(object value)
    {
        if (_bindingUpdating) return;
        PropertyInfo propertyInfo = GetPropertyInfo();
        if (propertyInfo == null) return;
        if (!propertyInfo.CanWrite)
            return;
        _propertyUpdating = true;
        try
        {
            propertyInfo.SetValue(AssociatedObject, value, null);
        }
        finally
        {
            _propertyUpdating = false;
        }
    }

    private PropertyInfo GetPropertyInfo()
    {
        if (_currentProperty != null && _currentProperty.Name == SourceProperty)
            return _currentProperty;
        if (AssociatedObject == null)
            throw new NullReferenceException("AssociatedObject is null.");
        if (string.IsNullOrEmpty(SourceProperty))
            throw new NullReferenceException("SourceProperty is null.");
        _currentProperty = AssociatedObject
            .GetType()
            .GetProperty(SourceProperty);
        if (_currentProperty == null)
            throw new NullReferenceException("Property not found in associated object, property name: " +
                                                SourceProperty);
        return _currentProperty;
    }

    #endregion
}

To use this class in XAML you need to add a reference to System.Windows.Interactivity library and add this namespaces:

xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:behaviors="clr-namespace:YOUR NAMESPACE WHERE YOU PUT THE PropertyManager CLASS"

You also need to specify the event that will be updated value, in this case PasswordChanged and specify a property that you want to bind, in this case Password:

<PasswordBox>
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="PasswordChanged">
            <behaviors:PropertyManager
                Binding="{Binding Path=MyPasswordProperty, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
                SourceProperty="Password" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</PasswordBox>

This class is versatile and can work with any of the properties also supports two-way binding.