Validating required selection in DropDownList

Question

My view model defines property which has to be displayed as combo box. Property definition is:

[Required]
public int Processor { get; set; }

I'm using DropDownListFor to render combo box:

<%=Html.DropDownListFor(r => r.Processor, Model.Processors, Model.Processor)%>

Model.Processors contains IEnumerable<SelectListItem> with one special item defined as:

var noSelection = new SelectListItem
  {
    Text = String.Empty,
    Value = "0"
  };

Now I need to add validation to my combo box so that user must select different value then 'noSelection'. I hoped for some configuration of RequiredAttribute but it doesn't have default value setting.

If the user is not supposed to select the "noSelection" why have you added it to the list of options? — Clicktricity, Jan 12 '11 at 18:31
If you ony want a blank as the initial option, use the overload of Html.DropDownListFor that takes a string as the prompt value: Html.DropDownListFor(r => r.Processor, Model.Processors, Model.Processor, String.Empty) then the required validation should work — Clicktricity, Jan 12 '11 at 19:05

score 26 · Accepted Answer · answered Jan 12 '11 at 18:43

26

How about this:

[Required]
public int? Processor { get; set; }

And then:

<%= Html.DropDownListFor(
    x => x.Processor, Model.Processors, "-- select processor --"
) %>

And in your POST action

[HttpPost]
public ActionResult Index(MyViewModel model)
{
    if (ModelState.IsValid)
    {
        // the model is valid => you can safely use model.Processor.Value here:
        int processor = model.Processor.Value;
        // TODO: do something with this value
    }
    ...
}

And now you no longer need to manually add the noSelection item. Just use the proper DropDownListFor overload.

answered Jan 12 '11 at 18:43

Darin Dimitrov

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1

Nice, I completely misunderstood that overload. Thanks. – Ladislav Mrnka Jan 12 '11 at 21:48
5

This does not validate on client side :( – Akira Yamamoto Apr 30 '14 at 14:47
This works for me ... perfect. So, instead of adding the default value directly to the model, you add it directly via the overload. – Legends Oct 28 '16 at 18:35
This worked for me too, but trying to figure out why? Any reason why this works and the other doesn't? – Ratan Oct 31 '16 at 15:09

score 0 · Answer 2 · edited May 23 '17 at 12:19

0

One possible issue is that jQuery Validate does run any rules if the value of an element is empty.

You can get around this by retriggering the validation when the user loses focus:

// select statements not firing null validation automatically
$("select").blur(function () { $(this).valid() });

edited May 23 '17 at 12:19

Community

1
1

answered Sep 28 '16 at 05:15

KyleMit

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Validating required selection in DropDownList

2 Answers2

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