Bind TextBox on Enter-key press

Question

The default databinding on TextBox is TwoWay and it commits the text to the property only when TextBox lost its focus.

Is there any easy XAML way to make the databinding happen when I press the Enter key on the TextBox?. I know it is pretty easy to do in the code behind, but imagine if this TextBox is inside some complex DataTemplate.

Answer 1

You can make yourself a pure XAML approach by creating an attached behaviour.

Something like this:

public static class InputBindingsManager
{

    public static readonly DependencyProperty UpdatePropertySourceWhenEnterPressedProperty = DependencyProperty.RegisterAttached(
            "UpdatePropertySourceWhenEnterPressed", typeof(DependencyProperty), typeof(InputBindingsManager), new PropertyMetadata(null, OnUpdatePropertySourceWhenEnterPressedPropertyChanged));

    static InputBindingsManager()
    {

    }

    public static void SetUpdatePropertySourceWhenEnterPressed(DependencyObject dp, DependencyProperty value)
    {
        dp.SetValue(UpdatePropertySourceWhenEnterPressedProperty, value);
    }

    public static DependencyProperty GetUpdatePropertySourceWhenEnterPressed(DependencyObject dp)
    {
        return (DependencyProperty)dp.GetValue(UpdatePropertySourceWhenEnterPressedProperty);
    }

    private static void OnUpdatePropertySourceWhenEnterPressedPropertyChanged(DependencyObject dp, DependencyPropertyChangedEventArgs e)
    {
        UIElement element = dp as UIElement;

        if (element == null)
        {
            return;
        }

        if (e.OldValue != null)
        {
            element.PreviewKeyDown -= HandlePreviewKeyDown;
        }

        if (e.NewValue != null)
        {
            element.PreviewKeyDown += new KeyEventHandler(HandlePreviewKeyDown);
        }
    }

    static void HandlePreviewKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Enter)
        {
            DoUpdateSource(e.Source);
        }
    }

    static void DoUpdateSource(object source)
    {
        DependencyProperty property =
            GetUpdatePropertySourceWhenEnterPressed(source as DependencyObject);

        if (property == null)
        {
            return;
        }

        UIElement elt = source as UIElement;

        if (elt == null)
        {
            return;
        }

        BindingExpression binding = BindingOperations.GetBindingExpression(elt, property);

        if (binding != null)
        {
            binding.UpdateSource();
        }
    }
}

Then in your XAML you set the InputBindingsManager.UpdatePropertySourceWhenEnterPressedProperty property to the one you want updating when the Enter key is pressed. Like this

<TextBox Name="itemNameTextBox"
         Text="{Binding Path=ItemName, UpdateSourceTrigger=PropertyChanged}"
         b:InputBindingsManager.UpdatePropertySourceWhenEnterPressed="TextBox.Text"/>

(You just need to make sure to include an xmlns clr-namespace reference for "b" in the root element of your XAML file pointing to which ever namespace you put the InputBindingsManager in).