c# - Object reference not set to an instance of an object with class -

i have situation have defined class within class, resembling following:

    public partial class proddata      {     private string prodid;     private string description;      ...and on until      private proddatachildren[] childitemsfield;      } 

proddatachildren it's own class, using identify sub-products may belong parent product, hence array.

in main part of program have loop reads in records, sort of like:

        while (myreader.read())         {             proddata productdatain = new proddata();             productdatain.id = "values assigned here"; 

until point there want assign child, getting error "object reference not set instance of object", using following statement

         productdatain.childitems[i].prodid = "string variable here";         } 

i beleive cause of error current childitems being set null, how supposed assign value it? need instantiate , instance of child item somehow , how this?

any appreciated, realize might no brainer some.

first of all, have initialize field before assigning collection. suggest using list instead of array:

public partial class proddata  {  ...and on until  private list<proddatachildren> childitemsfield = new list<proddatachildren>();  } 

with list you'll able following:

productdatain.childitems.add(new proddatachildren() { prodid = "string variable here" });