How to show checked radio button in Razor edit view Asp net core mvc

Question

Despite of Asp net core code in Razor view:

@model List<SelectListItem>
<form asp-controller="Manage" asp-action="Change" method="post">
    @foreach (SelectListItem item in Model) {
        <br />
        <input asp-for="@item.Value" type="radio" value="@item.Value" /> @(item.Value + " - " + item.Text)
   }
   <br />
   <input type="submit" value="OK" />
</form>

all radio buttons are checked in browser -> view source

<input type="radio" value="1001" checked="checked" id="item_Value" name="item.Value" /> 1001 - Vilnius<br />
<input type="radio" value="1002" checked="checked" id="item_Value" name="item.Value" /> 1002 - Palanga<br />

How it can be all radio buttons checked?

Added:

var lst = new List<SelectListItem>() {
           new SelectListItem {
                Value = "1001",
                Text = "Vilnius",
                Selected = true
            },
            new SelectListItem {
                Value = "1002",
                Text = "Trakai",
                Selected = false
            }
        };

Solution

As far as I know, the checked="checked" attribute is set because the current value of those radio buttons are equal to model value (the property you're assigned in asp-for attribute inside tag helper). Hence, your current setup with asp-for="@item.Value" is wrong here:

<input asp-for="@item.Value" type="radio" value="@item.Value" />

If you want to set their values based on Selected property inside SelectListItem instance, you need to use a property from your viewmodel class into asp-for attribute (the property must defined as value type or string).

Below is a proper example setup:

Model

// Viewmodel class
public class ViewModel
{
    // used to store selected value in select tag helper
    public string SelectedValue { get; set; }

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

Controller action

// Populate select list
[HttpGet]
public IActionResult Change()
{
    var model = new ViewModel();
    model.OptionList = new List<SelectListItem>();

    // populate list values here
    model.OptionList.Add(new SelectListItem { Text = "1001", Value = "Vilnius", Selected = true });
    model.OptionList.Add(new SelectListItem { Text = "1002", Value = "Trakai", Selected = false });

    return View(model);
}

View

@* Set viewmodel property into tag helper *@
@model ViewModel

<form asp-controller="Manage" asp-action="Change" method="post">
    @foreach (var item in Model.OptionList) 
    {
        <br />
        <input asp-for="SelectedValue" type="radio" value="@item.Value" /> @(item.Value + " - " + item.Text)
    }
    <br />
    <input type="submit" value="OK" />
</form>

Related issue:

Radio Button Tag Helper sets every radio button to checked

Comments

[Tetsuya Yamamoto]

Can you provide what kind of List<SelectListItem> passed to view? I think it's not a good idea to have List<SelectListItem> for @model directive.

[Sayed Mahmoud]

All radio button has checked!