MVC setting up Html.DropdownList on ModelState.IsValid = false

Question

This is something that has always puzzled me as to the best way round, while keeping maintainable code. The below code sets up a list of months and years for a payment gateway f

Answer 1

Add a private method to your controller (the following code assumes your ExpiryMonth and ExpiryYear properties are IEnumerable which is all that the DropDownListFor() method requires)

private void ConfigureViewModel(PayNowViewModel model)
{
  model.ExpiryMonth = Enumerable.Range(1, 12).Select(m => new SelectListItem
  {
    Value = m.ToString(),
    Text = m.ToString("00")
  });
  model.ExpiryYear = Enumerable.Range(DateTime.Today.Year, 10).Select(y => new SelectListItem
  {
    Value = y.ToString(),
    Text = y.ToString("00")
  });
}

and then in the GET method

public ActionResult ConfirmPayment()
{
  PayNowViewModel model = new PayNowViewModel();
  ConfigureViewModel(model);
  return View(model);
}

and in the POST method

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult ConfirmPayment(PayNowViewModel model)
{
  if (!ModelState.IsValid)
  {
    ConfigureViewModel(model);
    return View(model);
  }
  .... // save and redirect (should not be returning the view here)
}