Set multiple SelectList values on PostBack

Question

I have a form that contains a multiple selectlist and I also use bootstrap selectpicker with this.

code:

model:

    [Display(Name = "SystemTyp")]
    [Required(ErrorMessage = "Vänligen välj typ")]
    public List<SelectListItem> SystemTypes { get; set; }

view:

    <div class="form-group">
        @Html.Label("SystemTyp", new { @class = "col-md-2 control-label" })
        <div class="col-md-10">
            @Html.DropDownList("SystemTypes",
           RegistrationHandlers.GetSystemtypes()
           ,
           new { @class = "form-control", @multiple = "multiple", @title = "---  Välj Systemtyp  ---" })
            @Html.ValidationMessageFor(model => model.SystemTypes, "", new { @class = "text-danger" })
        </div>
    </div>

When posting:

Every time I post the list is empty. The list name matches the model property name.

What am I missing?

I have another list that is a single select so the selected value is a simple string and this works fine but the above is giving me a headache.

You `SelectList` property is named `SystemTypes` and the view code you have shown does not use that anywhere. All you have shown is a `DropDownList()` method that binds to a property named `UserRole` — , Sep 01 '16 at 11:41
`SystemTypes` is your `SelectList`. You cannot bind to a `SelectList`. Your property needs to be (say) `IEnumerable SystemTypes` (a ` — , Sep 01 '16 at 11:47
And do not use `DropDownList()` - use `ListBoxFor(m => m.SystemTypes, RegistrationHandlers.GetSystemtypes(), new { ... })` which is the correct way to generate a ` — , Sep 01 '16 at 11:48
@Stephen Muecke as of late you are like a guardian angel. thanks m8 — ThunD3eR, Sep 01 '16 at 11:53
hahahhahaha I like the (no-homo) edit. Developer skill level = precise — ThunD3eR, Sep 01 '16 at 12:02

teo van kot · Accepted Answer · 2016-09-01T11:57:19.723

2

You should inderstand that DropDownList helper creates select tag with name="SystemTypes" attribute in html markup.

On POST in passes selected value with UserRole name.

And you don't need whoule list on POST you need only selected value so create SystemTypeId property in your ViewModel and change your helper to this:

 @Html.DropDownList("SystemTypeId", <-- note this
           RegistrationHandlers.GetSystemtypes()
           ,
           new { @class = "form-control", @multiple = "multiple", @title = "---  Välj Systemtyp  ---" })

Then you will get selected value in your binded model.

Don't try to get whoulde list back - you don't need it.

If you need to select multiple you should use ListBox helper:

@Html.ListBox("SystemTypeIds", <-- note this
               RegistrationHandlers.GetSystemtypes()
               ,
               new { @class = "form-control", @title = "---  Välj Systemtyp  ---" })

SystemTypeIds property should be Array or IEnumerable<int> or IList<int> to bind correctry. (ofcource it could be not only int but string, bool etc..)

If you searching for best way to achive that i suggest you to use Strongly typed helper - ListBoxFor:

@Html.ListBoxFor(x => x.SystemTypeIds
               ,RegistrationHandlers.GetSystemtypes()
               ,new { @class = "form-control", @title = "---  Välj Systemtyp  ---" })

edited Sep 01 '16 at 11:57

answered Sep 01 '16 at 11:43

teo van kot

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Sorry, in my hase and frustration i copied the wrong code. Check edits. I want only the selected values – ThunD3eR Sep 01 '16 at 11:44
The thing you are describing is if i select only one item in the list. But when i select multiple? – ThunD3eR Sep 01 '16 at 11:46
1

I would suggest using the `ListBoxFor()` method, and passing the Model Property to it - saves headaches when refactoring :) – Geoff James Sep 01 '16 at 11:50
@teovankot Then suggest that, too. Yes we're here to help try and solve the OP's problem - but if we can suggest better practices to solve deeper issues, then bonus points all round! – Geoff James Sep 01 '16 at 11:53
Worked when i changed to IEnumerable and I tried using the listbox aswell and it works. Thanks! – ThunD3eR Sep 01 '16 at 11:55
@GeoffJames added, ok – teo van kot Sep 01 '16 at 11:55
1

`ListBox()` and `ListBoxFor()` add the `multlple` attribute :) – Sep 01 '16 at 11:56
@StephenMuecke ooops. my bad, didn't see that – teo van kot Sep 01 '16 at 11:57
@StephenMuecke fix – teo van kot Sep 01 '16 at 11:57

Set multiple SelectList values on PostBack

1 Answers1