Cannot implicitly convert type 'string' to 'System.Collections.Generic.List<string>'

Question

This question has probably been answered hundreds of times, but here goes.

I have this chunck of code:

private void PopulateStringDropdownList(List<ObjectInfo> listObject,
                                        object selectedType = null)
{
    List<string> listString = listObject.OrderBy(x => x.m_Type).ToString();
    for (int i = 0; i < listString .Count; i++)
    {
        for (int j = i + 1; j < listString .Count; j++)
        { 
            if (String.Equals(listString [i], listString [j]))
            {
                listString.RemoveAt(j);
            }
        }
    }
    ViewBag.property1 = new SelectList(listString );
}

So basically I'm trying to populate a dropdown List with strings coming from a property of each objects contained in the list I pass in parameter.

But the code doesn't compile because of the error you're seeing up there, and I've yet to understand why exactly. Any help anyone?

Answer 1

This is the problematic line:

List<string> listString = listObject.OrderBy(x => x.m_Type).ToString();

ToString returns a string, and you're trying to assign to a List<string> variable.

You need to do something like this:

List<string> listString = listObject.OrderBy(x => x.m_Type)
                                    .Select(x => x.ToString())
                                    .ToList();

This statement will order your listObject enumerable to the order that your want, then convert the values to strings, and finally convert the enumerable to a List<string>.

Answer 2

Look at this code:

List<string> listString = listObject.OrderBy(x => x.m_Type).ToString();

The right hand side expression is calling ToString() on the result of OrderBy - which isn't useful itself, and will result in a string.

You're then trying to assign that string expression to a new variable of type List<string>. That's not going to work.

I suspect you just want ToList instead of ToString:

List<string> listString = listObject.OrderBy(x => x.m_Type).ToList();

Answer 3

I think you want ToList instead of ToString.

Also, if all you're trying to do is remove duplicates, you can simply use LINQ and do this:

List<string> listString = listObject.OrderBy(x => x.m_Type).
    Select(x => x.ToString()).Distinct().ToList();