Selecting Values in Html.ListBox Creation

Question

I've been having trouble with this and haven't been able to find a way to solve my problem...

I have a select list that I want to allow users to select multiple of, and I'm using ASP.NET. After initially selecting them, I'd like them to be able to be able to edit their selection later. I'm having trouble with filling in the selected values when using ListBoxFor. I'm guessing the problem lies with the MultiSelectList.

I've tried using arrays, lists, and dictionaries to contain the selected values, but nothing is ever selected on the page it generates. By using a breakpoint and splitting the code so I can see the MultiSelectList, it seems that the SelectedValues property is always identical to what's passed into the constructor.

Model:

public class UniversityStrategicGoalsModel
{
    public Dictionary<string, string> goals { get; set; }

    public UniversityStrategicGoalsModel()
    {
        goals = new Dictionary<string, string>()
        {
            {"NA", "Not Applicable"},
            {"1.1","1.1 blah blah blah"},
            {"1.2","1.2 and many more strategic goals"}
        };
    }
}

Controller:

ProjectViewModel viewModel = new ProjectViewModel();
viewModel.Project = db.Projects.Find(id); // Gets unique project
viewModel.allGoals = new UniversityStrategicGoalsModel();
return View(viewModel);

View:

@Html.ListBoxFor(model => model.Project.UniversityGoals, new MultiSelectList(Model.allGoals.goals, "Key", "Value", Model.Project.UniversityGoals.Split(','))
// An example of model.Project.UniversityGoals could be "1.1,1.2"

Following this (using Lists of objects instead of Dictionaries) didn't help: http://ittecture.wordpress.com/2009/04/30/tip-of-the-day-198-asp-net-mvc-listbox-controls/

I also tried making a clone of the Dictionary, but with only the items I wanted and passing in an array of values (instead of keys) when my selected objects were in an Array (and again in a List).

I have edited your title. Please see, "Should questions include “tags” in their titles?", where the consensus is "no, they should not". — John Saunders
– John Saunders, Commented May 20, 2013 at 23:51
Sorry about that, I don't use Stack Overflow too much. It just seemed like my title was so general that a tag was necessary in order to properly name it. I thought about that beforehand, and I probably shouldn't have second-guessed myself. Alas, now I know about this naming convention :D — Pluto
– Pluto, Commented May 21, 2013 at 0:17
Surely you can still improve the title. What about "Selected Values in ListBox"? — John Saunders
– John Saunders, Commented May 21, 2013 at 0:20
Yeah I changed it slightly (even though I've found an answer already), but it seems you suggested that I change my title to what it already was lol :P — Pluto
– Pluto, Commented May 21, 2013 at 0:29

Ufuk Hacıoğulları · Accepted Answer · 2013-05-20 23:23:45Z

2

You need two properties for basic model binding. One is for filling the listbox, other is for keeping selected ones.

public class UniversityStrategicGoalsModel
{
    public Dictionary<string, string> Goals { get; set; }
    public IEnumerable<string> SelectedGoals { get; set; }


    public UniversityStrategicGoalsModel()
    {
        Goals = new Dictionary<string, string>()
        {
            {"NA", "Not Applicable"},
            {"1.1","1.1 blah blah blah"},
            {"1.2","1.2 and many more strategic goals"}
        };
    }
}

Then you create the listbox:

Html.ListBoxFor(model => model.SelectedGoals , 
                new MultiSelectList(Model.Goals, "Key", "Value"))

I simplified the model here, you get the idea.

answered May 20, 2013 at 23:23

Ufuk Hacıoğulları

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3 Comments

Pluto Over a year ago

The problem is that Model.SelectedGoals is a string (and it's strongly typed based on a database's contents), which is why I use the String.Split function to get the selected values.

Ufuk Hacıoğulları Over a year ago

@Pluto You can split it before creating the model and assign the values to SelectedGoals property. That would also keep this logic out of the view.

Pluto Over a year ago

Eh this means it'll have a new name and semantically change the source of the data in the ListBox, but at least it gets me to something that works. And in that case I'm just using a SelectList instead of a MultiSelect list.

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