Dictionary Constructor: System.ArgumentException : An item with the same key has already been added

Asked Mar 19 '15 at 09:53

Active May 01 '15 at 12:50

Viewed 397 times

A cache is initialized from another using the regular Dictionary constructor. for the first time, I get a

System.ArgumentException : An item with the same key has already been added.

private Dictionary<uint, Dictionary<ClassA, ClassB>> cache;
private void updateCache(Dictionary<uint, Dictionary<ClassA, ClassB>> otherCache) 
{
  cache = new Dictionary<uint, Dictionary<ClassA, ClassB>>(otherCache); // Raises the exception
}

I verified that cache and othercache really have the same type.

How is this even possible ?!

edited May 01 '15 at 12:50

keenthinker

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asked Mar 19 '15 at 09:53

Mikaël Mayer

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Its not, unless the other cache ha inherited from dictionary which allows for duplciates. Can you do a GroupBy key and Count, and see which key is causing it to throw? – Michal Ciechan Mar 19 '15 at 09:55
Linq does not work in the Immediate window. I'll try modifying the code (which is not mine) – Mikaël Mayer Mar 19 '15 at 09:56
yes, you need to figure out how a duplicate got into `otherCache` – Michal Ciechan Mar 19 '15 at 09:57
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http://stackoverflow.com/a/139626/442444 – Carbine Mar 19 '15 at 10:02
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Have you checked that "otherCache" has the default comparer? – Yoh Deadfall Mar 19 '15 at 10:18
@YohDeadfall Another `uint` comparer can't possibly be *less* restrictive than the default comparer, can it? – Rawling May 01 '15 at 13:21
@YohDeadfall Interesting! I didn't even known you could [initialize a dictionary with a custom `IEqualityComparer`](https://msdn.microsoft.com/en-us/library/ms132072(v=vs.110).aspx). – Jeff B May 01 '15 at 13:22
@Rawling Another `uint` comparer may contain a bug which allows to have two equal keys, I think. – Yoh Deadfall May 07 '15 at 07:37

Dictionary Constructor: System.ArgumentException : An item with the same key has already been added

0 Answers0