how to add a null list to list of list ?

Question

Hi all I have a list its name is TP that may be a null or has data and have a list of list vairable its name is history. I want to add the TP list to history with help of a counter winc. int winc = 1; List TP ; List > history = new List >() ; When I run the code below gives exception invalid index or arument An ArgumentOutOfRangeException  history[winc-1].AddRange (TP.ToList ()); winc++; I slould say in first time my TP list is null and TP.count() is 0. Please help Thanks

Vulpes · Answer

If history has no elements already you can simply do: history.Add(TP); and the elements will automatically be given the correct index. However if history already has elements and you want to replace the one at index winc -1 you can do: history[winc - 1] = TP; Finally if history already has elements but you want to insert one at index winc -1 you can do: history.Insert(winc - 1 TP); Notice that if TP is not null it should refer to a different List each time you add replace or insert an element if you don't want elements to be duplicated.

Vulpes · Answer

history[winc - 1] = TP; will give an exception if there are no elements in history. Just use history.Add(TP). TP will then be added at index history.Count which of course will be 0 to start with.

diamond diamond · Answer

Thanks TP takes its data from this db and sc. List TP = db.Intersect(sc).ToList (); Vulpes I changed my code to history[winc - 1] = TP; but still gives an exception My history does not already any data. winc is counter for time window I want TP in every time windows dropped to history and I specified contains of history with time window. It means which tp list realated to which time window in history. I tested this was ok history.Insert(winc - 1 TP); Thanksssss Vulpes

Arpit Jain · Answer

You need to initialize the TP first. Right now it's just a reference of type List. Try List tp=new List (); And also i guess you need to do this only AddRange(TP); Because TP is already a list.