A two-dimensional ArrayList returns System.String[]

Question

I have trouble with the value that arraylist returns.

I created a two-dimensional Arraylist that includes string arrays, when I try to get actual value of string arrays, I get System.String[] as output instead of actual value of the arrays.

Why do I get System.String() as outuput?

Here is my code :

static void Main(string[] args)
{
    string[] employee_1 = { "Employee1" };
    string[] employee_2 = { "Employee2" };

    ArrayList main_array = new ArrayList();

    main_array.Add(employee_1);
    main_array.Add(employee_2);

    for (int i= 0; i < 2; i++) 
    {
        Console.WriteLine(main_array[i]);                
    }
    Console.ReadKey();
}

Answer 1

That is because when retrieving the items from an ArrayList what you are getting is a reference to an object instead of the actual type. Thus when printing it is calls the ToString of object (which prints the type's name) and not the string you want. In addition when printing a collection (like you are doing in your WriteLine command) you need to specify how to so do because it's default implementation is also as object's. You can use string.Join to print all items in the nested array.

To correct this first cast to string[] ( as string[]) and then print, or better still is to work with the list object instead: List<string[]>. To read more see:

• ArrayList vs List<> in C#
• What is the difference between an Array, ArrayList and a List?

So:

var mainCollection = new List<string[]> { new string[] { "Employee1" },
                                          new string[] { "Employee2" }};
for (int i = 0; i < mainCollection.Count; i++) 
{
    Console.WriteLine(string.Join(", ", mainCollection[i]));
}
Console.ReadKey();

---

As a side note do not loop to 2 but instead by the number of items in the collection. See: What is a magic number, and why is it bad?

Answer 2

This is the default behaviour of ToString() function for an array.

To print the employees names, you need to iterate the array:

for (int i= 0; i < 2; i++) 
{
    foreach(string employee in main_array[i]) {
        Console.WriteLine(employee);
    }
}

Answer 3

The problem is here, ArrayList always take input as an object. So, when you add string array at an ArrayList, it take an object instead of string array.

So, you should convert this object to string array and print it. like below:

        for (int i = 0; i < 2; i++)
        {
            Console.WriteLine(string.Join(", ", main_array[i] as string[]));
        }

or may use below(both are same):

        for (int i = 0; i < 2; i++)
        {
            foreach (string employee in main_array[i] as string[])
            {
                Console.WriteLine(employee);
            }
        }

Answer 4

Because you have string[] type elements in outer ArrayList. The best examples to enumerate are in answers above. If you realy need string content of string to be wtitten you should use

Console.WriteLine(((string[])main_array[i])[0]);

Answer 5

main_array is a two position ArrayList, each position contains a string[] this is, a string array.

If you use main_array[0], this is a reference to employee_1 which is a string array.

You should be able to reference the array strings by using main_array[0][0]

Try this:

foreach(var strArray in main_array)
{
    // strArray is a string array
    foreach(var stir in strArray)
    {
        // star is a string
        Console.WriteLine(str);
    }
}