Creating a joined string from an object that refers to an array of structs or classes

Question

How to correctly get String.Join to handle an array when it is referred by object likely with some casting to IEnumerable?

object myArray = new int[]{1,2,3};
Console.WriteLine(String.Join(",", myArray)); // prints System.Int32[]

Particular context:

I have a view in which I receive a list of properties via reflection. These can be single items as well as collections. I wish to print them (the single value or a joined string).

How can I convert a collection to a joined string? I tried (among other things) the following, but this does not work:

@foreach (PropertyInfo cell in Model.GetData().ToList())
{
    <td>
    @{ object value = cell.GetValue(row, null);}
    @(cell.IsCollection() ?
        String.Join(", ", (value as IEnumerable<object>)
            .Select(o => o.ToString()).Select(o => o.ToString())) : value)
    </td>
 }

Info:

• Cells' type is PropertyInfo.
• Value is either an object or an object[]. The object or items in the object array can be a string, a boolean or a integer
• IsCollection is a self written (and tested) extension method which returns true when the PropertyInfo Cell contains a Collection as value

UPDATE: The following does not work either:

if (cell.IsCollection())
{
     values = String.Join(", ", (IEnumerable<object>)value);                              
}

This gives the following error:

Can't convert type System.Collections.Generic.List'1[System.Int32] to type System.Collections.Generic.IEnumerable'1[System.Object].'

Note that:

IEnumerable<object>)value

This works.

String.Join(", ", (IEnumerable<object>)value)

Throws an error of type System.EntryPointNotFoundException

Does anyone know how I can do this correctly?

Answer 1

Just simply:

var joinedString = String.Join(", ", value as IEnumerable<object>);

And this:

.Select(o => o.ToString()).Select(o => o.ToString())

is wrong. Because:

// cast to `IEnumerable` of type `object`
(value as IEnumerable<object>)  

// convert to IEnumerable<string>
.Select(o => o.ToString())

// join everything to one string
String.Join(", ", ...)

// and then you again call select on `string`
// which operates on IEnumerable<char>
.Select(o => o.ToString())) 

So as you see, you need to remove these two Select calls.

UPDATE:

Oh, I see. You cannot cast IEnumerable<struct> to IEnumerable<object> due to language restrictions.

LINK

Try this:

// you need to cast to non-generic `IEnumerable`
// then use `Cast` extension method to convert to generic enumerable
IEnumerable<object> valueAsEnumerable = ((IEnumerable)value).Cast<object>();

// then use it in `string.join`
var joinedString = String.Join(", ", valueAsEnumerable);