Error on calling 'OnMarketData' method on bar -1: Collection was modified

[NinjaCustomer]

> Error on calling 'OnMarketData' method on bar -1: Collection was modified; enumeration operation may not execute.




What would this signify? my IsDataSeriesRequired = false, Calculate is OnEachTick no other defaults have been changed except description and name.

At first I was thinking to add a CurrentBar < 1 check in OnMarketData but re-reading the message, I don't think that would help, right?

How can I avoid this error?

[NinjaTrader_JoshG]

Hello NinjaCustomer,
Thanks for your post.

In general, this error is caused when you are iterating over a collection and modifying it at the same time. For example, if you were using a foreach loop on a list, and removing an item or adding an item to that list in the loop.

Can you show use the specific snippet that is causing this error?

[NinjaCustomer]

ah I see the part before the colon is just saying what bar it occurred on, I'm not entirely sure what code it is as I use OnMarketData in several indicators and columns

I suspect I know what MarketAnalyzer column is causing it but it loops through several HashSets, Dictionaries and Lists so it will take some time to figure out. Would it be ok just to have the MarketAnyalyzerColumn lock these things while it processes them?

... I think the problem might be that I'm using IEnumerable (when I'm using .Where() ) on some lists and such and passing that around, I guess if I change that to ToList() this should solve my problems.

[NinjaTrader_JoshG]

NinjaCustomer,

Since this is a C# error message you can likely find any information by searching google for the message itself.

Perhaps "collection was modified enumeration operation may not execute c#" would be a good start point

[NinjaCustomer]

yes thanks, I realized after doing some searches that the text right of the colon was an actual C# error. I'll keep that in mind in the future when I see similar messages with events and colons.

note to self:

c# - Collection was modified; enumeration operation may not execute - Stack Overflow

c# - IEnumerable Where() and ToList() - What do they really do? - Stack Overflow