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Hello,

cannot implicitly convert type 'bool?' to 'bool'. An explicit conversion exists (are you missing a cast?) in MVC.

I am trying checkbox in my mvc application but its getting error.

@Html.CheckBoxFor(x => x.IsSelected) error in "IsSelected".

Please help me.

Thanks in Advance.

Ankit Agarwal
Software Engineer

What I have tried:

C#
[HttpPost]
        public string Index(IEnumerable<City> cities)
        {
            if (cities.Count(x => x.IsSelected) == 0)
            {
                return "You didn't select any city";
            }
            else
            {
                StringBuilder sb = new StringBuilder();
                sb.Append("You selected -");
                foreach (City city in cities)
                {
                    if (city.IsSelected)
                    {
                        sb.Append(city.Name + ",");
                    }
                }
                sb.Remove(sb.ToString().LastIndexOf(","), 1);
                return sb.ToString();
            }
        }



@Html.CheckBoxFor(x => x.IsSelected)
Posted
Updated 15-Dec-16 17:02pm
Comments
F-ES Sitecore 15-Dec-16 4:19am
   
If IsSelected is a model designed to be mapped to a checkbox then it should be defined as "bool" and not "bool?" as a checkbox only has two states, not three. If possible change the definition of IsSelected.

Do this:

C#
if (cities.Count(x => x.IsSelected == true) == 0)
   
Comments
Richard Deeming 15-Dec-16 12:43pm
   
You're getting too far ahead - you've answered his next question! :D

And the one after that will probably be about the if (city.IsSelected) line.
#realJSOP 15-Dec-16 13:01pm
   
I try to answer as many questions as possible with one answer.
Try with this

C#
@Html.CheckBoxFor(x => x.IsSelected.GetValueOrDefault())
   
v2
Comments
Richard Deeming 15-Dec-16 13:05pm
   
This will result in an InvalidOperationException with the message "Templates can be used only with field access, property access, single-dimension array index, or single-parameter custom indexer expressions".
If you can't change the model property from bool? to bool, then you're going to have to use the CheckBox and LabelFor methods, rather than the CheckBoxFor method:
@Html.CheckBox(nameof(Model.IsSelected), Model.IsSelected ?? false)
@Html.LabelFor(m => m.IsSelected)

Alternatively, you could use EditorFor with a custom editor, as described in this StackOverflow answer[^].

Or, you could add a non-nullable wrapper property to your viewmodel, and use that with the CheckBoxFor method:
C#
public bool IsSelectedNotNull
{
    get { return IsSelected ?? false; }
    set { IsSelected = value; }
}
@Html.CheckBoxFor(m => m.IsSelectedNotNull)
   
Usually, I would modify the view model and if the view model only purpose is to be a model for that view, you can always modify it.

Alternatively, if I would have many cases where I prefer to have a bool ? for a property and still have a check box, I would probably write an extension method that would handle that case.

Doing that however require to have a good understanding of C# as expression trees are somewhat unusual...
   

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