Umbraco-CMS/src/Umbraco.Web/Mvc/ViewDataContainerExtensions.cs

using System.Web.Mvc;

namespace Umbraco.Web.Mvc
{
    internal static class ViewDataContainerExtensions
    {
        private class ViewDataContainer : IViewDataContainer
        {
            public ViewDataContainer()
            {
                ViewData = new ViewDataDictionary();
            }
            public ViewDataDictionary ViewData { get; set; }
        }

        /// <summary>
        /// Creates a new IViewDataContainer but with a filtered ModelState
        /// </summary>
        /// <param name="container"></param>
        /// <param name="prefix"></param>
        /// <returns></returns>
        public static IViewDataContainer FilterContainer(this IViewDataContainer container, string prefix)
        {
            var newContainer = new ViewDataContainer();
            newContainer.ViewData.ModelState.Merge(container.ViewData.ModelState, prefix);
            //change the HTML field name too
            newContainer.ViewData.TemplateInfo.HtmlFieldPrefix = prefix;
            return newContainer;
        }

        /// <summary>
        /// Returns a new IViewContainer based on the current one but supplies a different model to the ViewData
        /// </summary>
        /// <param name="container"></param>
        /// <param name="model"></param>
        /// <returns></returns>
        public static IViewDataContainer CopyWithModel(this IViewDataContainer container, object model)
        {
            return new ViewDataContainer
                {
                    ViewData = new ViewDataDictionary(container.ViewData)
                        {
                            Model = model
                        }
                };
        }

    }
}