Foreach System.NullReferenceException: Object reference not set to an instance of an object

Question

I get System.NullReferenceException: Object reference not set to an instance of an object in this:

var offeredItems = new List<ulong>(Trade.steamMyOfferedItems);
foreach (var item in offeredItems) {
    Trade.RemoveItem(item);
}

What is different than in all such questions is that the exception is in line 3 from this code block. Does it mean that Trade is null? That would be strange because I make this check a few operations earlier:

if (Trade != null && Trade.OtherSID == OtherSID) {
    OnTradeMessage(message);
    return;
}

The only reason for this would be if Trade was nulled in another thread (and that would be very unecxpected behaviour) in time of 5-10 simple operations, this would be really very strange.

EDIT:

The problem is I can't reproduce this doing the exact same steps. I guess Trade has to be null and it has to be nulled in other thread, there is no other option. Sorry for stupid question.

EDIT2:

If Trade.RemoveItem is executed, then offeredItems is not empty, hence Trade cannot be null. In both cases offeredItems should contain 1-2 elements. So as far as I know (and understand):

Trade is not null, Trade is an object of class Trade, which has method RemoveItem (the exception is thrown exactly at this line: Trade.RemoveItem(item);, not in RemoveItem, RemoveItem is not null delegate (this code works most of the time)

Do you have other threads executing that could be setting that to null? At any rate, see the related questions list to the right. There are a million of these questions and the solution is the same. Find out what's null and fix it or validate against it. — Anthony Pegram
– Anthony Pegram, Commented May 31, 2013 at 23:56
Do you think item exist in Trade? It might not be found - My guess — codingbiz
– codingbiz, Commented Jun 1, 2013 at 0:05
Almost all cases of NullReferenceException are the same. Please see "What is a NullReferenceException in .NET?" for some hints. — John Saunders
– John Saunders, Commented Jun 1, 2013 at 0:16
Are you able to run the code in a debugger so it pauses execution when the exception is thrown? If so, once it pauses, check the value of Trade and other relevant information. This should help you determine what's gone wrong. — Sam
– Sam, Commented Jun 1, 2013 at 4:19

Community · Accepted Answer · 2020-06-20 09:12:55Z

3

the exception is in line 3 from this code block

Does it mean that Trade is null?

It could mean that. It sounds like one of the following possibilities:

Trade is null.
Trade is a property whose getter throws a NullReferenceException.
RemoveItem is a null delegate.
RemoveItem throws a NullReferenceException.

Why don't you step through the code in a debugger and find out? Also, please see the comments to your question.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jun 1, 2013 at 0:18

Sam

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