I'm developing an ASP.NET MVC 5 application, with C# and .NET Framework 4.6.1.
I have this View:
@model MyProject.Web.API.Models.AggregationLevelConfViewModel
[...]
@Html.DropDownListFor(m => m.Configurations[0].HelperCodeType, (SelectList)Model.HelperCodeTypeItems, new { id = "Configurations[0].HelperCodeType" })
The ViewModel is:
public class AggregationLevelConfViewModel
{
private readonly List<GenericIdNameType> codeTypes;
private readonly List<GenericIdNameType> helperCodeTypes;
public IEnumerable<SelectListItem> CodeTypeItems
{
get { return new SelectList(codeTypes, "Id", "Name"); }
}
public IEnumerable<SelectListItem> HelperCodeTypeItems
{
get { return new SelectList(helperCodeTypes, "Id", "Name"); }
}
public int ProductionOrderId { get; set; }
public string ProductionOrderName { get; set; }
public IList<Models.AggregationLevelConfiguration> Configurations { get; set; }
public AggregationLevelConfViewModel()
{
// Load CodeTypes to show it as a DropDownList
byte[] values = (byte[])Enum.GetValues(typeof(CodeTypes));
codeTypes = new List<GenericIdNameType>();
helperCodeTypes = new List<GenericIdNameType>();
for (int i = 0; i < values.Length; i++)
{
GenericIdNameType cType = new GenericIdNameType()
{
Id = values[i].ToString(),
Name = EnumHelper.GetDescription((CodeTypes)values[i])
};
if (((CodeTypes)values[i]) != CodeTypes.NotUsed)
codeTypes.Add(cType);
helperCodeTypes.Add(cType);
}
}
}
And Models.AggregationLevelConfiguration is:
public class AggregationLevelConfiguration
{
public byte AggregationLevelConfigurationId { get; set; }
public int ProductionOrderId { get; set; }
public string Name { get; set; }
public byte CodeType { get; set; }
public byte HelperCodeType { get; set; }
public int PkgRatio { get; set; }
public int RemainingCodes { get; set; }
}
I need to set selected value in these properties:
public IEnumerable<SelectListItem> CodeTypeItems
{
get { return new SelectList(codeTypes, "Id", "Name"); }
}
public IEnumerable<SelectListItem> HelperCodeTypeItems
{
get { return new SelectList(helperCodeTypes, "Id", "Name"); }
}
But I can't set it in new SelectList(codeTypes, "Id", "Name"); or new SelectList(helperCodeTypes, "Id", "Name"); because the selected value are in Configurations array: fields AggregationLevelConfiguration.CodeType and AggregationLevelConfiguration.HelperCodeType.
I think I have to set selected value in the View, but I don't know how to do it.
How can I set the selected values?
Unfortunately @Html.DropDownListFor() behaves a little differently than other helpers when rendering controls in a loop. This has been previously reported as an issue on CodePlex (not sure if its a bug or just a limitation)
The are 2 option to solve this to ensure the correct option is selected based on the model property
Option 1 (using an EditorTemplate)
Create a custom EditorTemplate for the type in the collection. Create a partial in /Views/Shared/EditorTemplates/AggregationLevelConfiguration.cshtml (note the name must match the name of the type
@model yourAssembly.AggregationLevelConfiguration
@Html.DropDownListFor(m => m.HelperCodeType, (SelectList)ViewData["CodeTypeItems"])
.... // other properties of AggregationLevelConfiguration
and then in the main view, pass the SelectList to the EditorTemplate as additionalViewData
@using (Html.BeginForm())
{
...
@Html.EditorFor(m => m.Configurations , new { CodeTypeItems = Model.CodeTypeItems })
...
Option 2 (generate a new SelectList in each iteration and set the selectedValue)
In this option your property CodeTypeItems should to be IEnumerable<GenericIdNameType>, not a SelectList (or just make codeTypes a public property). Then in the main view
@Html.DropDownListFor(m => m.Configurations[0].HelperCodeType, new SelectList(Model.CodeTypeItems, "Id", "Name", Model.Configurations[0].HelperCodeType)
Side note: there is no need to use new { id = "Configurations[0].HelperCodeType" - the DropDownListFor() method already generated that id attribute
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