what I am doing wrong here with List

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List<int> processedList = new List<int>();
            processedList = (List<int>) Session["processedUsers"];

I am getting argument null reference exception here????

XML

if(processedList.Count != 0)
{
  Boolean exists =  processedList.Contains(i);
    if (!exists)
    {
    }

I am getting Null reference exception even

Boolean exists = processedList.Exists(element => element ==i)

The session state list can be empty. Still I have run this test.
Please advise.

Posted 19-Oct-10 22:58pm

Jayadheer Reddy

Updated 19-Oct-10 23:27pm

LittleYellowBird

v4

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voloda2 · Answer 1 · 2010-10-19T23:28:00

Solution 1

You overwrite your processedList instance with a value from Session. So if there is no list instance in the session, you will get this exception.

So you probably don't have correctly initialized Session["processedUsers"] and thus you have exception.

Posted 19-Oct-10 23:28pm

voloda2

OriginalGriff · Answer 2 · 2010-10-19T23:36:00

Put simply,

C#

List<int> processedList = new List<int>();

Creates processedList and assignes a new, empty list to it.

processedList = (List<int>) Session["processedUsers"];

Replaces the empty list with whatever the cast returns.

if(processedList.Count != 0)

Uses the list contained in processedList to check the number of entries.

So if Session["processedUSers"] does not return a list then:
if it returns a non-list item it will throw a "cannot convert" exception.
if it returns a null, processedUsers will become null, and the empty list you assigned will be discarded.

If processedUsers is null, then attempting to access any element, even the items count, will give a null reference exception.

So: Check what Session["processedUSers"] is returning, and make sure that processedItems is a valid list before you try and use3 it.