How to iterate through items in a list box

function SelectItemFromListBox(listControl:OleVariant, listValue:string): boolean;
var 
i, itemIndex: integer;
begin
result := false;

itemIndex := -1;

for i := 0 to listControl.wItemCount - 1 do
begin
 if listControl.wItem[i] = Value then
 begin
  itemIndex := i;
  break;
 end; 
end;

if itemIndex < 0 then
begin
Log.Error('Item value ''' + VarToStr(listValue) + ''' not found in list control ' + VarToStr(listControl.FullName), nil, nil, nil, listControl.Picture);
exit;
end;

listControl.Keys('[Home]');

for i := 0 to itemIndex - 1 do
listControl.Keys('[Down]');
result := true;
end;

wItemCount - to get the list count.

wClickItem - to click the item based on the index or value.

More information, You can refer the NisHera post.

Hope these links would help you 

https://support.smartbear.com/testcomplete/docs/app-objects/specific-tasks/standard/combobox/drop-down-lists.html?q=dropdown+list#_ga=1.113965838.809719160.1405381514

https://support.smartbear.com/testcomplete/docs/app-objects/specific-tasks/standard/combobox/determining-number-of-items.html