c# - Error System.Collections.Generic.List`1[System.String] when itry String.Join on a list of result

Question

I am getting the error System.Collections.Generic.List`1[System.String] when i try to use String.Join in a list of result.

For instance i have two list like this:

var list1= new List<string>{"string1","string2"};
var list2= new List<string>{"string1"};

Then i want to get a message with the string that doesn't appear on list2

var resultList1 = list1.Except(list2).ToList(); // this line get a list with "string2"

when i use String.Join i get the error System.Collections.Generic.List`1[System.String]. Also i tried resultList1.Cast<List>() instead resultList1 with same outcome.

var message = "List strings not found:

"
                + String.Join(",", $"

{resultList1}

");

question from:https://stackoverflow.com/questions/65853173/error-system-collections-generic-list1system-string-when-itry-string-join-on

Answer 1

You need to use the string join like ths,

var message = "List strings not found:

" + String.Join(",", resultList1);

You are using the system join on an enumerable array but when you use $" {result1} " string interpolation, you are basically joining a single string which doesn't work.

String.Join takes in a string (comma, newline or any string) that combines all elements from an array but when you give string instead of array or collection, it will give the error.

Lastly, Documentation should help explain more about the usage in depth.