Unable to cast object of type 'System.Collections.Generic.List`1[System.Object]' to type 'System.Collections.Generic.List`1[customType]

Question

I have ArrayList which contains 4 items. each item is of type List<object> . I am trying to get first item from ArrayList using below code. but it throws error

Unable to cast object of type 'System.Collections.Generic.List 1[System.Object]' to type 'System.Collections.Generic.List 1[CustomType]

calling code -

ArrayList arrayList = BusinessLayer.GetData();
List<CustomType> tempList = (List<CustomType>)arrayList[0];

called code logic -

if (connection.State == System.Data.ConnectionState.Closed)
                    connection.Open();

                var command = connection.CreateCommand();
                command.CommandText = "EXEC SP_GET_DATA @id";
                command.Parameters.Add(new SqlParameter("@id", id));
                using (var reader = command.ExecuteReader())
                {
                    var customTypeList = ((IObjectContextAdapter)context)
                            .ObjectContext
                            .Translate<object>(reader)
                            .ToList();

                    arrayList.Add(customTypeList);
        
                   reader.NextResult();

                   var customType2List = ((IObjectContextAdapter)context)
                            .ObjectContext
                            .Translate<object>(reader)
                            .ToList();

                    arrayList.Add(customType2List);
              }

I am returning arraylist and want to get data back at calling code. I don't want to use model in called code. I understand that, we can use model at called code but I have to verify whether using ArrayList, can we get data back? I hope I explained clearly.

here I am trying to cast List<object> from ArrayList to List<CustomType>

Answer 1

You have to explicitly cast back to List of Object first. Then use Cast to the custom type.

ArrayList arrayList = new();

arrayList.Add(new List<object>() { new Person() { FirstName = "Bob", LastName = "NewHart"} });

var tempList = ((List<object>)arrayList[0]).Cast<Person>().ToList();

Console.WriteLine(tempList[0].FirstName);
Console.ReadLine();

public class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}