I want to achieve that in a DataGrid a column displays TimeSpan values as hh:mm and users are only able to input values in such a format. I did this with a TextBox some time ago by implementing a user control encapsulating the TextBox and a IValueConverter which takes care of value conversion.

However recently I read that user controls should be the last resort and there are easier ways like using attached properties. I found this approach for TextBoxes (/a/34085735/5772806) but I am unable to adapt it to DataGridColumns as the BindingExpression is not part of DataGridTextColumn but of its nested TextBox.

This is what I do have at the moment:

public static class DataGridTimeColumnBehavior
{
    public static readonly DependencyProperty IsTimeColumnProperty =
    DependencyProperty.RegisterAttached(
        "IsTimeColumn",
        typeof(bool),
        typeof(DataGridTimeColumnBehavior),
        new PropertyMetadata(false, OnIsTimeColumnChanged));

    public static bool GetIsTimeColumn(DependencyObject obj)
    {
        return (bool)obj.GetValue(IsTimeColumnProperty);
    }

    public static void SetIsTimeColumn(DependencyObject obj, bool value)
    {
        obj.SetValue(IsTimeColumnProperty, value);
    }

    private static readonly DependencyProperty OriginalBindingExpressionProperty = DependencyProperty
        .RegisterAttached(
            "OriginalBindingExpression", typeof(BindingExpression), typeof(TextBoxExtensions),
            new PropertyMetadata(default(BindingExpression)));

    private static void SetOriginalBindingExpression(DependencyObject element, BindingExpression value)
    {
        element.SetValue(OriginalBindingExpressionProperty, value);
    }

    private static BindingExpression GetOriginalBindingExpression(DependencyObject element)
    {
        return (BindingExpression)element.GetValue(OriginalBindingExpressionProperty);
    }

    private static void OnIsTimeColumnChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (d is DataGridTextColumn column)
        {
            if (GetOriginalBindingExpression(column) == null)
            {
                // DataGridTextColumn does not contain a definition for GetBindingExpression
                SetOriginalBindingExpression(column, column.GetBindingExpression(TextBox.TextProperty));
            }
            BindingExpression bindingExpression = GetOriginalBindingExpression(column);

            Binding parentBinding = bindingExpression.ParentBinding;
            Binding newBinding = new Binding(parentBinding.Path.Path)
            {
                ElementName = parentBinding.ElementName,
                Path = parentBinding.Path,
                Mode = parentBinding.Mode,
                Converter = new TimeSpanStringConverter(),
                UpdateSourceTrigger = parentBinding.UpdateSourceTrigger,
            };
            foreach (ValidationRule validationRule in parentBinding.ValidationRules)
            {
                newBinding.ValidationRules.Add(validationRule);
            }
            // DataGridTextColumn does not contain a definition for SetBinding
            column.SetBinding(TextBox.TextProperty, newBinding);
        }
    }
}