Bug 15889 - System.Collections.Generic.Dictionary.ContainsKey(), Array index is out of range.
Summary: System.Collections.Generic.Dictionary.ContainsKey(), Array index is out of ra...
Alias: None
Product: Android
Classification: Xamarin
Component: Mono runtime / AOT Compiler ()
Version: 4.8.x
Hardware: PC Windows
: --- normal
Target Milestone: ---
Assignee: Jonathan Pryor
Depends on:
Reported: 2013-11-02 06:39 UTC by Justin Caldicott
Modified: 2017-08-07 20:38 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Justin Caldicott 2013-11-02 06:39:51 UTC

We updated to 4.8.x recently, and have done our first release to Beta testers since this.

One of these testers (running a Samsung GT-I9300 (Android 4.1.2 Phone)) is consistently seeing exceptions, which AFAIK shouldn't happen.  Nothing changed in our code that is likely to have affected it.

The MS documentation on Dictionary.ContainsKey() indicates that the only exception you should expect from this is ArgumentNullException: http://msdn.microsoft.com/en-us/library/kw5aaea4(v=vs.110).aspx

It hasn't happened for any of our other (9) testers, even though one of them has the same device and OS version.

Any help would be greatly appreciated.  I don't want to deploy this build beyond our testers until I've fixed this.

Best wishes,

Comment 1 Jonathan Pryor 2013-11-02 16:43:16 UTC
Can you provide the complete stack trace?

Is the Dictionary being accessed in a multi-threaded fashion?
Comment 2 Justin Caldicott 2013-11-02 17:45:26 UTC
No, there's only the one thread using the Dictionary AFAIK.  Multiple dictionary instances have shown the problem for the same user.  Both stack traces are below.  They're both during application startup.

Let me know if you need any more detail.  This started after upgrading to 4.8.x, though I don't recall what version we were using before that.

Many thanks for the prompt response.

Best wishes,


Message: Array index is out of range.

Stack trace:
at System.Collections.Generic.Dictionary`2<BirdJournal.Data.Taxon, bool>.ContainsKey (BirdJournal.Data.Taxon) <0x00094> 
at LfFramework.Collections.UniqueList`1<BirdJournal.Data.Taxon>.Add (BirdJournal.Data.Taxon) <0x0003b> 
at BirdJournal.Data.TaxonomicSequence..ctor (System.Collections.Generic.IEnumerable`1<BirdJournal.Data.Taxonomy>) <0x004df> 
at BirdJournal.Data.TaxonomicConfig..ctor (BirdJournal.Data.Taxonomy,BirdJournal.Data.Taxonomy,System.Collections.Generic.IEnumerable`1<BirdJournal.Data.Taxonomy>) <0x003a7> 
at BirdJournal.Mobile.Application.InitialiseDatabase () <0x000ef> 
at BirdJournal.Droid.AndroidApplication.OnCreate () <0x0023b> 
at Android.App.Application.n_OnCreate (intptr,intptr) <0x00037> 
at (wrapper dynamic-method) object.b1c03069-7310-40ce-8482-ec950fd0a7d7 (intptr,intptr) <0x0003b>

Message: Array index is out of range.

Stack trace:
at System.Collections.Generic.Dictionary`2<BirdJournal.Data.Concept, bool>.ContainsKey (BirdJournal.Data.Concept) <0x00094> 
at LfFramework.Collections.UniqueList`1<BirdJournal.Data.Concept>.Add (BirdJournal.Data.Concept) <0x0003b> 
at LfFramework.Collections.UniqueList`1<BirdJournal.Data.Concept>.AddRange (System.Collections.Generic.IEnumerable`1<BirdJournal.Data.Concept>) <0x0009b> 
at BirdJournal.Data.Location.get_Concepts () <0x000af> 
at BirdJournal.Data.Location.get_Concepts () <0x0009f> 
at BirdJournal.Data.Location.get_Concepts () <0x0009f> 
at BirdJournal.Data.Location.get_Concepts () <0x0009f> 
at BirdJournal.Data.Database.updateAllConceptsIndex () <0x00037> 
at BirdJournal.Data.Database.updateConcepts () <0x00dbb> 
at BirdJournal.Data.Database.Init (string,bool,BirdJournal.Data.Platform,BirdJournal.Data.DatabasePathInfo,BirdJournal.Data.Database/TaxonMigrationEventHandler,bool) <0x00533> 
at BirdJournal.Mobile.Application.InitialiseDatabase () <0x00063> 
at BirdJournal.Droid.AndroidApplication.OnCreate () <0x0023b> 
at Android.App.Application.n_OnCreate (intptr,intptr) <0x00037> 
at (wrapper dynamic-method) object.6eea678b-b2aa-4c46-b7a9-f86bcdfaaf8e (intptr,intptr) <0x0003b>
Comment 3 Jonathan Pryor 2013-11-04 13:54:08 UTC
Alas, I can't imagine why this would be happening. :-(

Would it be possible for you to create a small testcase that reproduces the exception?

 - Jon
Comment 4 Justin Caldicott 2013-11-04 16:10:50 UTC
Hi Jon,

I'm not able to reproduce it locally, it's only happening on this one user's device.

Not sure how to progress this.. is there more logging that I can enable for him somehow?


Comment 5 Jonathan Pryor 2013-11-04 16:48:20 UTC
@Justin: Which device is this?

As for what else to do, you could do this:


Add a plain text-file to your .csproj, set the Build action to AndroidEnvironment, and add:


IFF this is a Debug build (i.e. debug symbols are on the target device...), then the exception will contain line numbers, which will narrow down where within ContainsKey() things are going bad:


EIther it's Dictionary.table (line 481) or it's Dictionary.linkSlots or keySlots (line 487) which is generating the exception; it would be handy to know which.

Though it doesn't look possible for line 481 to throw (due to the % operator use), suggesting it's the linkSlots/keySlots access which is failing, which in turn suggests that the "linked list" behavior of the hashtable is at fault...

...which means it would be _really_ handy to have an actual test case. :-(
Comment 6 Justin Caldicott 2013-11-04 17:40:59 UTC

It's a UK Samsung GT-I9300 (Android 4.1.2) phone.

I'm just waiting for those changes to run through our build system and I'll get them to the tester and hopefully get more detail.

I'll post back when I have more data.


Comment 7 Jon Douglas [MSFT] 2017-08-07 20:38:59 UTC
Thank you for taking the time to submit this report. After reviewing the description of this bug, we believe it no longer affects the current version of Xamarin.Android. If you are still experiencing the issue after updating your packages, please reopen this report with an attached reproduction.