A specific routine is getting called twice when i run my application

i implement this code from this url https://msdn.microsoft.com/en-us/library/windows/hardware/ms171625%28v=vs.90%29.aspx

i saw when i run my code first time then a function called SupplyPageOfData() is calling twice. i like to understand the reason.

here is the code for the routine SupplyPageOfData()

public DataTable SupplyPageOfData(int lowerPageBoundary, int rowsPerPage)
        {
            // Store the name of the ID column. This column must contain unique
            // values so the SQL below will work properly.
            if (columnToSortBy == null)
            {
                columnToSortBy = this.Columns[0].ColumnName;
            }

            if (!this.Columns[columnToSortBy].Unique)
            {
                throw new InvalidOperationException(String.Format(
                    "Column {0} must contain unique values.", columnToSortBy));
            }

            // Retrieve the specified number of rows from the database, starting
            // with the row specified by the lowerPageBoundary parameter.
            command.CommandText = "Select Top " + rowsPerPage + " " +
                CommaSeparatedListOfColumnNames + " From " + tableName +" WHERE " + columnToSortBy + " NOT IN (SELECT TOP " +
                lowerPageBoundary + " " + columnToSortBy + " From " +
                tableName + " Order By " + columnToSortBy +") Order By " + columnToSortBy;
            adapter.SelectCommand = command;

            DataTable table = new DataTable();
            table.Locale = System.Globalization.CultureInfo.InvariantCulture;
            adapter.Fill(table);
            return table;
        }