ModelState Import/Export

ModelStateTempDataAttribute.cs

/// <summary>
/// Base class for Import/Export ModelState From/To TempData action filters
/// </summary>
public abstract class ModelStateTempDataAttribute : ActionFilterAttribute
{
    protected static readonly string Key = typeof(ModelStateTempDataAttribute).FullName;
}

/// <summary>
/// Import ModelState from previous ActionMethod from TempData
/// </summary>
/// <remarks>This allows the ModelState from one action result to be used in another ActionResult</remarks>
public class ImportModelStateAttribute : ModelStateTempDataAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        ModelStateDictionary modelState = filterContext.Controller.TempData[Key] as ModelStateDictionary;

        if (modelState != null)
        {
            // Only import if we are viewing
            if (filterContext.Result is ViewResult)
            {
                filterContext.Controller.ViewData.ModelState.Merge(modelState);
            }
            else
            {
                filterContext.Controller.TempData.Remove(Key);
            }
        }

        base.OnActionExecuted(filterContext);
    }
}

/// <summary>
/// Export ModelState from ActionMethod to TempData
/// </summary>
/// <remarks>This allows the ModelState from one action result to be used in another ActionResult</remarks>
public class ExportModelAttribute : ModelStateTempDataAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        if (!filterContext.Controller.ViewData.ModelState.IsValid)
        {
            // Export if we are redirecting
            if ((filterContext.Result is RedirectResult) || (filterContext.Result is RedirectToRouteResult))
            {
                filterContext.Controller.TempData[Key] = filterContext.Controller.ViewData.ModelState;
            }
        }

        base.OnActionExecuted(filterContext);
      }
  }