how can i convert arraylist to string[]? [duplicate]

Are you still using .NET 1.1. or why don't you use typed List<T> instead of an ArrayList?

First, you cannot cast a DataRow to String. You can cast every field of a DataRow to a string.

If you can use Linq you can use following code to get a String[] of all row fields where each field is separated by comma:

String[] rowFields = DtSet.Tables[0]
                    .AsEnumerable()
                    .Select(r => string.Join(",", r.ItemArray));
                    .ToArray();

You cannot take a DataRow (type) and add it to an ArrayList expecting it to be a string. A DataRow is an object that has a myriad of information about the object as well as the objects data.

foreach(DataRow dtRow in dtSet.Tables[0].Rows)
{
    myArrayList.Add(dtRow["UserName"].ToString());
}

string[] myArray = myArrayList.ToArray(typeof(string));

You are placing a number of DataRow objects into an ArrayList. DataRows are not strings. So: that can't work. At best, you can perhaps get the .ToString(), but frankly, that isn't going to be all that helpful - because every row will just say System.Data.DataRow (since it doesn't override ToString(). I think you need to re-evaluate what you are trying to do.

Example based on comment discussion:

DataTable table = ...
string[] strings = new string[table.Rows.Count];
int idx = 0;
foreach(DataRow row in table.Rows)
{
    StringBuilder sb = new StringBuilder();
    object[] cells = row.ItemArray;
    for(int i = 0 ; i < cells.Length ; i++)
    {
        if (i != 0) sb.Append(',');
        sb.Append('"').Append(cells[i]).Append('"');
    }
    strings[idx++] = sb.ToString();
}

You have an ArrayList whose elements are of type DataRow. You are trying to convert it into an array of strings. A DataRow is not a string (nor does it become one on downcasting), so you can't do that.

If the array of strings is what you ultimately want, you should probably call ToString (or whatever conversion you need) on each element while filling the ArrayList.

(Also, as Tim Schmelter said in comments, you should really be using a List<T> for some T -- probably either string or DataRow, depending on exactly how your code ends up looking -- rather than an ArrayList.)

Each item the arrayList is of type DataRow, you can't cast it to a string.

Instead, you should construct a string that represents the contents of the row, and add that string to the list, e.g.

myArrayList.Add(dtRow["CustomerName"]);

Have you tried this:

string[] array = myArrayList.ToArray(typeof(string)) as string[];

ArrayList myArrayList = new ArrayList();

myArrayList.Add("as");
myArrayList.Add("as");
myArrayList.Add("as");
myArrayList.Add("as");
myArrayList.Add("as");            
myArrayList.Add("as");

string[] array = myArrayList.ToArray(typeof(string)) as string[];
foreach (var item in array)
{
    Console.WriteLine(item.ToString());                
}

Output:

as
as
as
as
as
as