Question

I am trying to update a compound page model which as one of its properties has a list of objects.

My Model looks like this:

public class PageViewModel 
{
    public ProgramListVM ProgramsDDL { get; set; }

    public PageViewModel()
    {
        this.ProgramsDDL = new ProgramListVM();
    }
}

The ProgramListVM class is:

public class ProgramListVM
{
    public List<ProgramVM> Program_List { get; set; }
    public int SelectedValue { get; set; }

    public ProgramListVM()
    {
        this.Program_List = new List<ProgramVM>();
        this.SelectedValue = 0;
    }
}

and ProgramVM is:

public class ProgramVM
{
    public int ProgramID { get; set; }
    public string ProgramDesc { get; set; }

    public ProgramVM(int id, string code)
    {
        this.ProgramID = id;
        this.ProgramDesc = code;
    }
}

I try to render this dropdownlist by the following two:

1-

  <%: Html.DropDownList("ProgramsDDL", new SelectList(Model.Page6VM.ProgramsDDL.Program_List, "ProgramID", "ProgramDesc", Model.Page6VM.ProgramsDDL.SelectedValue))%>

2-

 <%: Html.DropDownListFor(m => m.Page6VM.ProgramsDDL.Program_List, new SelectList(Model.Page6VM.ProgramsDDL.Program_List, "ProgramID", "ProgramDesc"), Model.Page6VM.ProgramsDDL.SelectedValue)%>

But when I try to update my model through a controller action

[HttpPost]
    public ActionResult UpdateUser(PageViewModel model)  
    {
    }

model.ProgramsDDL.count is zero.

What is the best way to render this dropdownlist and be able to set the selected index, and also be able to send the selected index back to the controller?

Answer 1

You mixed up the parameters for Html.DropDownListFor(). Code sample below should work.

<%: Html.DropDownListFor(m => m.SelectedValue, 
                              new SelectList(Model.Page6VM.ProgramsDDL.Program_List, "ProgramID", "ProgramDesc"), 
                              null) %>

You also should have a SelectedValue in your model that’s posted back.

public class PageViewModel 
{
    public ProgramListVM ProgramsDDL { get; set; }
    public int SelectedValue { get; set; }

    public PageViewModel()
    {
        this.ProgramsDDL = new ProgramListVM();
    }
}

Also default model binder can’t map complex collections to your model. You probably don’t need them in your post action anyway.