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MVC – Set selected value of SelectList

Posted by: admin December 10, 2017 Leave a comment

Questions:

How can I set the selectedvalue property of a SelectList after it was instantiated without a selectedvalue;

SelectList selectList = new SelectList(items, "ID", "Name");

I need to set the selected value after this stage

Answers:

If you have your SelectList object, just iterate through the items in it and set the “Selected” property of the item you wish.

foreach (var item in selectList.Items)
{
  if (item.Value == selectedValue)
  {
    item.Selected = true;
    break;
  }
}

Or with Linq:

var selected = list.Where(x => x.Value == "selectedValue").First();
selected.Selected = true;

Questions:
Answers:

A bit late to the party here but here’s how simple this is:

ViewBag.Countries = new SelectList(countries.GetCountries(), "id", "countryName", "82");

this uses my method getcountries to populate a model called countries, obviousley you would replace this with whatever your datasource is, a model etc, then sets the id as the value in the selectlist. then just add the last param, in this case “82” to select the default selected item.

[edit] Here’s how to use this in Razor:

@Html.DropDownListFor(model => model.CountryId, (IEnumerable<SelectListItem>)ViewBag.Countries, new { @class = "form-control" })

Hope this saves someone some time.

Questions:
Answers:

Why are you trying to set the value after you create the list? My guess is you are creating the list in your model instead of in your view. I recommend creating the underlying enumerable in your model and then using this to build the actual SelectList:

<%= Html.DropDownListFor(m => m.SomeValue, new SelectList(Model.ListOfValues, "Value", "Text", Model.SomeValue)) %>

That way your selected value is always set just as the view is rendered and not before. Also, you don’t have to put any unnecessary UI classes (i.e. SelectList) in your model and it can remain unaware of the UI.

Questions:
Answers:

Simply use the third parameter for selected value in mvc4

@Html.DropDownList("CountryList", new SelectList(ViewBag.Countries, "Value", "Text","974"))

Here “974” is selected Value Specified

In my result selected country is now qatar.in C# as below`

    foreach (CountryModel item in CountryModel.GetCountryList())
        {
            if (item.CountryPhoneCode.Trim() != "974")
            {
                countries.Add(new SelectListItem { Text = item.CountryName + " +(" + item.CountryPhoneCode + ")", Value = item.CountryPhoneCode });

            }
            else {


                countries.Add(new SelectListItem { Text = item.CountryName + " +(" + item.CountryPhoneCode + ")", Value = item.CountryPhoneCode,Selected=true });

            }
        }

Questions:
Answers:

Further to @Womp answer, it’s worth noting that the “Where” Can be dropped, and the predicate can be put into the “First” call directly, like this:

list.First(x => x.Value == "selectedValue").Selected = true;

Questions:
Answers:

I needed a dropdown in a editable grid myself with preselected dropdown values. Afaik, the selectlist data is provided by the controller to the view, so it is created before the view consumes it. Once the view consumes the SelectList, I hand it over to a custom helper that uses the standard DropDownList helper. So, a fairly light solution imo. Guess it fits in the ASP.Net MVC spirit at the time of writing; when not happy roll your own…

public static string DropDownListEx(this HtmlHelper helper, string name, SelectList selectList, object selectedValue)
{
    return helper.DropDownList(name, new SelectList(selectList.Items, selectList.DataValueField, selectList.DataTextField, selectedValue));
}

Questions:
Answers:

Doug answered my question… But I’ll explain what my problem was exactly, and how Doug helped me solve my problem which you could be encountering.

I call jquery $.post and am replacing my div with my partial view, like so.

function AddNewAddress (paramvalue) {
    $.post(url, { param: paramvalue}, function(d) {
        $('#myDiv').replaceWith(d);
    });
}

When doing so, for some reason when stepping into my model my selected value affiliated property was never set, only until I stepped into the view it came into scope.

So, What I had before

@Html.DropDownListUnobtrusiveFor(model => model.CustomerAddresses[i].YearsAtAddress, Model.CustomerAddresses[i].YearsAtAddressSelectList, new {onchange = "return Address.AddNewAddress(this,'" + @Url.Action("AddNewAddress", "Address") + "'," + i + ")"})

however even though Model.CustomerAddresses[i].YearsAtAddressSelectList, was set… it didn’t set the selected value.

So after….

 @Html.DropDownListUnobtrusiveFor(model => model.CustomerAddresses[i].YearsAtAddress, new SelectList(Model.CustomerAddresses[i].YearsAtAddressSelectList, "Value", "Text", Model.CustomerAddresses[i].YearsAtAddress), new { onchange = "return Address.AddNewAddress(this,'" + @Url.Action("AddNewAddress", "Address") + "'," + i + ")" })

and it worked!

I decided not to use DropDownListFor as it has problem when using unobtrusive validation, which is why i reference the following if your curious in a class classed

HtmlExtensions.cs




[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList)
{
    return DropDownListUnobtrusiveFor(htmlHelper, expression, selectList, null /* optionLabel */, null /* htmlAttributes */);

}


[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, object htmlAttributes)
{
    return DropDownListUnobtrusiveFor(htmlHelper, expression, selectList, null /* optionLabel */, new RouteValueDictionary(htmlAttributes));

}


[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, IDictionary<string, object> htmlAttributes)
{
    return DropDownListUnobtrusiveFor(htmlHelper, expression, selectList, null /* optionLabel */, htmlAttributes);

}


[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, string optionLabel)
{
    return DropDownListUnobtrusiveFor(htmlHelper, expression, selectList, optionLabel, null /* htmlAttributes */);

}


[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, string optionLabel, object htmlAttributes)
{
    return DropDownListUnobtrusiveFor(htmlHelper, expression, selectList, optionLabel, new RouteValueDictionary(htmlAttributes));

}


[SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters", Justification = "Users cannot use anonymous methods with the LambdaExpression type")]

[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]

public static MvcHtmlString DropDownListUnobtrusiveFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IEnumerable<SelectListItem> selectList, string optionLabel, IDictionary<string, object> htmlAttributes)
{
    if (expression == null)
    {
        throw new ArgumentNullException("expression");
    }


    ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);



    IDictionary<string, object> validationAttributes = htmlHelper
        .GetUnobtrusiveValidationAttributes(ExpressionHelper.GetExpressionText(expression), metadata);



    if (htmlAttributes == null)
        htmlAttributes = validationAttributes;
    else
        htmlAttributes = htmlAttributes.Concat(validationAttributes).ToDictionary(k => k.Key, v => v.Value);



    return SelectExtensions.DropDownListFor(htmlHelper, expression, selectList, optionLabel, htmlAttributes);

}

Questions:
Answers:

You can use below method, which is quite simple.

new SelectList(items, "ID", "Name",items.Select(x=> x.Id).FirstOrDefault());

This will auto-select the first item in your list. You can modify the above query by adding a where clause.

Questions:
Answers:

I usually use this method

        public static SelectList SetSelectedValue(SelectList list, string value)
    {
        if (value != null)
        {
            var selected = list.Where(x => x.Value == value).First();
            selected.Selected = true;
            return list;
        }
        return list;
    }

Questions:
Answers:

I wanted the dropdown to select the matching value of the id in the action method. The trick is to set the Selected property when creating the SelectListItem Collection. It would not work any other way, perhaps I missed something but in end, it is more elegant in my option.

You can write any method that returns a boolean to set the Selected value based on your requirements, in my case I used the existing Equal Method

public ActionResult History(long id)
        {
            var app = new AppLogic();
            var historyVM = new ActivityHistoryViewModel();

            historyVM.ProcessHistory = app.GetActivity(id);
            historyVM.Process = app.GetProcess(id);
            var processlist = app.GetProcessList();

            historyVM.ProcessList = from process in processlist
                                    select new SelectListItem
                                    {
                                        Text = process.ProcessName,
                                        Value = process.ID.ToString(),
                                        Selected = long.Equals(process.ID, id)                                    

                                    };

            var listitems = new List<SelectListItem>();

            return View(historyVM);
        }

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