Question

I’m trying to create this helper method and not sure how to handle the indexing on this. I keep getting index out of bounds when it hits the new class initializer in my helper:

public static void AddColumn(this ColumnElementType[] columnListToAddTo,
                             string name, string value)
{
    // Add a new column to the column list
    columnListToAddTo[columnListToAddTo.Length] = new ColumnElementType
            {
                 NAME = name,
                 VALUE = value
            };
}

Example setting up and using the helper:

        ColumnElementType[] columns =  new ColumnElementType[3];
        columns.AddColumn(Constants.EmailColumnName, email);
        columns.AddColumn(Constants.FirstNameColumnName, firstName);
        columns.AddColumn(Constants.LastNameColumnName, lastName);

Answer 1

This doesn’t work, since columnListToAddTo[columnListToAddTo.Length] will always return 3 (the length of the array you declared). Therefore:

• you are trying to add each element at an invalid index (3; valid would be 0..2)
• even if you use Length-1, you would always put the new element at the same array location (overwriting the reference to the previously added element)

Also, since an array cannot be extended (you’d have to copy the contents to a new, larger array), I would also suggest to use a List<ColumnElementType> or alternatively an ArrayList (if you can’t use generics).

If you still want to use an array, then you should extend your helper method to take an index parameter, where to add the new element, e.g:

ColumnElementType[] columns =  new ColumnElementType[3];
int index = 0;
columns.AddColumn(Constants.EmailColumnName, email, index++);
columns.AddColumn(Constants.FirstNameColumnName, firstName, index++);
columns.AddColumn(Constants.LastNameColumnName, lastName, index++);

//...

public static void AddColumn(..., int index)
{
  // Add a new column to the column list
  columnListToAddTo[index] = new ColumnElementType { ... };
}