Using DropDownListFor with model

Question

On my view I am using a list as my model and each list item is of type model, so it looks like this:

@model IEnumerable<UserManager.Models.vw_UserManager_Model>

and I am trying to loop through this list and add a specific property to a DropDownListFor:

@for (int i = 0; i < Model.Count(); i++)
{
    Html.DropDownListFor(model => model.ElementAt(i).module, new SelectList(Model, Model.ElementAt(i).module));
}

But when I do this it doesn't render a dropdownmenu on my page.

Image of my list in locals

Can someone help?

Levi Botelho · Accepted Answer · 2012-11-30 12:53:38Z

2

You can't render a dropdown list for a model because there is no way of representing the model in its entirety in a dropdown. What is ASP.NET supposed to render?

What you can do if you would like to select a model from a list is to run a LINQ Select query on the list, whereby you create an IEnumerable<SelectListItem> like this:

var selectList = Model
    .Select(x => new SelectListItem
    {
        Name = x.module_name,
        Value = x.module
    });

I have tried to take the values from the screenshot that you posted. Apologies if I made an error. You get the idea...

What this code does is loop through the collection of your object type (Model.Select) and returns a collection of SelectListItem. If you are unfamiliar with LINQ you need to think of Select as a transformative function. It takes a collection, and for each element transforms it into something else and returns the result. Here, it takes each element of the Model collection and creates a SelectListItem. It then returns an IEnumerable<SelectListItem>.

To render the list on the page you do the following:

@Html.DropDownListFor(Model.MyValue, selectList)

...where Model.MyValue is the variable which receives the selected value (assuming that the value, model is a string, which it appears to be).

edited Nov 30, 2012 at 12:53

answered Nov 30, 2012 at 11:57

Levi Botelho

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5 Comments

nick gowdy Over a year ago

I can't get your code to work. selectList does not exist in current context. Am I missing something?

Levi Botelho Over a year ago

selectList is the IEnumerable<SelectListItem> that I defined in the first code block! You need to do that bit first.

nick gowdy Over a year ago

I feel confused because I am new to using LINQ. If on my view my model is a list collection with each item in that collection an object and each object has module property with a value. How do I loop through this collection and take the module value?

Levi Botelho Over a year ago

A Select expression does the looping for you (which is what I did). To loop through a collection and take the module value you do collection.Select(x => x.module) which will return an IEnumerable<type of the module property>. This is exactly what I am doing in my answer, except that I am merging a couple steps and doing what you want to do more concisely.

nick gowdy Over a year ago

Thanks I now understand how it works. I ended up using this code: @Html.DropDownListFor(model => model.FirstOrDefault().module, Model.Select(x => new SelectListItem{Text = x.module, Value = x.module}))

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