Displaying specific Enum Values in a Dropdown in Asp.Net Mvc

Question

I have an Enum Class with 4 statuses which are Created, Dispatched, Delivered and Delayed in that respective order.

Currently, all 4 of these appear in the dropdown on my Edit Delivery page.

What I want is, if my status is Created then I should ONLY be able to change it to Dispatched, if my status is Dispatched I should ONLY be able to change it to Delivered or Delayed, and if my status is Delayed I should ONLY be able to change it to Dispatched or Delivered.

This should all happen on my Edit Delivery page. You'll also notice that I don't want Created in either of the lists above as I only require it in Create Delivery.

So, essentially I want to achieve is when my delivery status is set to Created, I should only see Dispatched in my Enum Dropdown when I wish to Edit that Delivery. Similarly for Dispatched, if my status is set to dispatched then I only want to see Delivered or Delayed. Same for Delayed, I only want to see Dispatched and Delivered.

I'm fairly new to MVC and if anyone can suggest a solution for this, I'll greatly appreciate it!

Please let me know if any additional code is required and I will add it to the question.

Enum Class:

public enum Status
{
    Created, Dispatched, Delivered, Delayed
}

Delivery View Model:

public class DeliveryVM
{
    public int? ID { get; set; }
    public Status Status { get; set; }
}

Delivery Edit View:

        <div class="form-group">
            @Html.LabelFor(model => model.Status, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EnumDropDownListFor(model => model.Status, htmlAttributes: new { @class = "form-control", @id="dropdown" })
                @Html.ValidationMessageFor(model => model.Status, "", new { @class = "text-danger" })
            </div>
        </div>

vendettamit · Accepted Answer · 2015-09-30 13:25:11Z

You have to use a custom select list instead of using EnumDropDownListFor() helper method.

First define a strategy to get the next respective list of collection. See this class StrategicStatesExtension below that can give you respective list of states as you defined. Class is defining extension methods so that you can use the method in fluent style. Note: Keeping the current status in the next possible statuses to show in the form as default selected item.

public static class StrategicStatesExtension
{
    public static Status[] Created
    {
        get
        {
            return new [] { Status.Created, Status.Dispatched };
        }
    }

    public static Status[] Dispatched
    {
        get
        {
            return new [] { Status.Delayed, Status.Delivered, Status.Dispatched };
        }
    }

    public static Status[] Delayed
    {
        get
        {
            return new [] { Status.Delivered, Status.Dispatched, Status.Delayed };
        }
    }

    public static Status[] GetAssociatedValidStatus(this Status currentStatus)
    {
        switch (currentStatus)
        {
            case Status.Created:
                return Created;
            case Status.Dispatched:
                return Dispatched;
            case Status.Delayed:
                return Delayed;
            case Status.Delivered:
                return Status.Delivered;
            default:
                throw new ArgumentOutOfRangeException("Invalid current state received.");
        }
    }

    public static List<SelectListItem> ToDropDownList(this Status[] sourceStates)
    {
        List<SelectListItem> items = new List<SelectListItem>();

        foreach (var item in sourceStates)
        {
            items.Add(
                new SelectListItem { 
                        Value = item.ToString("d"), // Value of enum (short)
                        Text = item.ToString() // Name of enum
                });
        }

        return items;
    }

The usage of this strategy extension method would be like:

public class DeliveryVM
{
    public int? ID { get; set; }
    public Status Status { get; set; }

    public List<SelectListItem> States { get; set; }

    public DeliveryVM()
    {
        // Sample usage: only for demo you need to call this in other method
        // e.g. where your model is being filled with data.
        this.States = Status.GetAssociatedValidStatus().ToDropDownList();    
    }

}

Atlast instead of using @Html.EnumDropDownListFor you need to build the List with new property States from either ViewData or from ModelProperty

From ViewData:

@Html.DropDownListFor("Statuses",
(List<SelectListItem>)ViewData["Statuses"],"value", "text", htmlAttributes: new { @class = "form-control", @id="dropdown" })

From Model property:

@Html.DropDownListFor("Statuses",
(model.Statuses,"value", "text", htmlAttributes: new { @class = "form-control", @id="dropdown" })

Tried this method out as well, and it works, but I decided to go with Stephen's answer above instead. It was based on code he's helped me with before. Thank you though!
No problem. Glad the problem is solved. :) I'm not a big fan of If..Else ladders so I avoid them as much as possible to increase the readability of code.

score 2 · Accepted Answer · 2015-09-30 09:24:41Z

2

The EnumDropDownListFor() method will generate options for each item in the enum. Instead you need to use the `DropDownListFor() method.

Add an additional property to you view model for the SelectList

public class DeliveryVM
{
  public int? ID { get; set; }
  [Required(ErrorMessage = "Please select the status")]
  public Status Status { get; set; }
  public SelectList StatusList { get; set; } // add this      
}

Then in you GET method, build the options you need based on the existing Status. Note you only need to build a list of string representing the enum values because the DefautModelBinder will convert the posted stringvalue to the corresponding enum value when you post.

Delivery delivery = // get your data model
DeliveryVM model = new DeliveryVM
{ 
  ID = ... // set other properties based on data model
};
// Build list of options basd on current status
List<string> options = new List<string>();
if (delivery.Status == HealthHabitat.Models.Status.Created)
{
  model.Status = HealthHabitat.ViewModels.Status.Dispatched; // its the only choice so set as the default selection
  options.Add(HealthHabitat.ViewModels.Status.Dispatched.ToString());
}
else if (delivery.Status == HealthHabitat.Models.Status.Dispatched)
{
  options.Add(HealthHabitat.ViewModels.Status.Delivered.ToString());
  options.Add(HealthHabitat.ViewModels.Status.Delayed.ToString());
}
else if (delivery.Status == HealthHabitat.Models.Status.Delayed)
{
  options.Add(HealthHabitat.ViewModels.Status.Dispatched.ToString());
  options.Add(HealthHabitat.ViewModels.Status.Delivered.ToString());
}
model.StatusList = new SelectList(options);
return View(model);

And in the view

@Html.LabelFor(m => m.Status, new { @class = "control-label col-md-2" })
@Html.DropDownListFor(m => m.Status, Model.StatusList, "Please select",  new { @class = "form-control" }) // unclear why you are changing the id attribute?
@Html.ValidationMessageFor(m => m.Status, new { @class = "text-danger" })

In the POST method, the selected value will be correctly bound to the Status property of your view model

Side note: Not clear what you what to do when the current status is Delivered (perhaps not render any control?) and if the current status is Created you only allow one choice (Dispatched) so it seems unnecessary to render a control in that case also.

edited Sep 30, 2015 at 9:24

answered Sep 30, 2015 at 1:50

user3559349

3 Comments

mustang00 Over a year ago

Hmm, I think the Status in the ViewModel is conflicting with Status in the Model. I applied this to status HealthHabitat.ViewModels.Status.Dispatched and I tried this HealthHabitat.Models.Status.Dispatched but neither work. Any ideas?

user3559349 Over a year ago

Do you have 2 different enums (one for the data model and one for the view model)?

user3559349 Over a year ago

Ah, Now I remember you previous question. I have updated the answer with what I think you need based on your use of 2 separate enums.

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