Question

You can create a dropdownlist using

@Html.DropDownListFor(model => model.SelectedId, model.DropDownItems);

but where does DropDownListFor get the value to pass into the model => model.SelectedId lambda from?

Answer 1

SelectedId is just the integer of the field in the model.

the model is passed in from the controller using

return View(myModel);

And the model can be defined in the view at the top

@model mymodelnamespace.RoomBookingInsert

So the dropdownbox’s value is set as the SelectedId field in your model.

A proper field name for example would be RoomNo if that clarifies it better.

@Html.DropDownListFor(model => model.RoomNo, model.Rooms);

As long as model.DropDownItems (or model.Rooms in my example) Contains a item with the value of that attribute, it will set it as the selected item in the list as default.

Edit:

If you are using viewbag, rather than the model, instead use DropDownList. (each input has a for extension for use with models)

@Html.DropDownList("RoomNo", 
       new SelectList(ViewBag.Rooms as System.Collections.IEnumerable ?? Enumerable.Empty<SelectListItem>(), "RoomNo", "RoomName"),
       new { @value = @ViewBag.RoomNo})

This above, creates an input form with id RoomNo,

and uses a SelectList that will default to empty if null. The fields that defined the values and text shown are set at the end of the select list parameters.

The last bit sets the default value to the contents of @ViewBag.RoomNo.

You can also create the select list in the controller, and then simply set the dropdown options to the viewbag.myselectList entity.