Hi, What may be the problem is that Android is destroying you singleton class. Android does not ensure that static classes/members will keep their values. On lower end devices, the garbage collector is obviously working hard to keep memory usage at a minimum.
If you wish to do something like this, you can create an instance of whatever class, and assign it to a member on a derived Application. I also had this problem with my application, so I changed the class to be an instance class. I then created a class that derived from Android.App.Application (remember the [Application] attribute). And in the application's OnCreate, I created an instance of my no-longer-static class. This did help. You can then access you Application by using (MyApplication)Context.ApplicationContext. Hope this is useful (and if inaccurate, please don't hesitate to inform me) Regards, Matthew L. On Mon, Jun 25, 2012 at 12:49 PM, keith <ke...@buzzinteractive.co.uk> wrote: > Hi > I have been getting random null reference exceptions in my app when running > on lower end devices (galaxy ace in this case), but not on a desire s or > emulators. They mostly seem to be in and around my data access to sqlite > (using sqlite-net) although I haven't been able to pin point them to any > one > bit of code. Generally it will crash with the only stacktrace being that > there was a null reference exception and nothing to indicate where and so I > have been using logging to try to get an idea of the source of the issues > but it seems to shift around. Then today the debugger actually caught one > of these occurences but when checking out the variables in scope 'this' was > null (I have a screen shot if you would like it as in theory this isn't > possible). 'this' being a singleton instance of a class which was running > some data updates on a background thread (started from my activity using > ThreadPool.QueueUserWorkItem(state => _dp.CheckCacheAge()); ). At this > point there is not a lot going on in the current activity which is simply > waiting on the updates and has some event handlers attached to update the > ui > with progress. This particular crash happened at a point where there is > not > a great deal loaded into memory. > > stacktrace: > > System.NullReferenceException: Object reference not set to an instance of > an > object > at (wrapper stelemref) object:virt_stelemref_class (intptr,object) > at MyDevon.DataProvider.PopulateConfiguration () [0x0001b] in > /Projects/NVG/Around Me Android/branches/My Devon/Around > Me/DataAccess/DataProvider.cs:225 > > The log from another occurence (included last reference to garbage > collection): > > 06-25 11:22:09.119: D/Mono ( 3076): GC_MINOR: pause 37.06ms, bridge > 0.00ms promoted 912K major 5008K los 7416K > ..... > 06-25 11:22:09.659: D/SQLite(3076): ExecuteNonQuery > 06-25 11:22:09.659: D/SQLite(3076): ExecuteNonQuery > 06-25 11:22:09.659: D/SQLite(3076): ExecuteNonQuery > 06-25 11:22:09.669: D/MD-DataProvider(3076): started insert > 06-25 11:22:09.669: D/SQLite(3076): ExecuteNonQuery > 06-25 11:22:09.669: I/mono(3076): Stacktrace: > 06-25 11:22:09.679: E/mono(3076): [0x7f5420:] EXCEPTION handling: > System.NullReferenceException: Object reference not set to an instance of > an > object > > These crashes are intermitent as in they do not occur in the same place > each > time and only occur roughly 1 in every 3 runs of the full update routine. > There doesn't seem to be any correlation with timings of the GC either, but > it does feel like something external is killing off my static instance of > this class. > > Any advice of where to look on this one would be very helpful as I'm > completely at a loss. > > thanks > > Keith > > > -- > View this message in context: > http://mono-for-android.1047100.n5.nabble.com/this-is-null-null-reference-exception-tp5710505.html > Sent from the Mono for Android mailing list archive at Nabble.com. > _______________________________________________ > Monodroid mailing list > Monodroid@lists.ximian.com > > UNSUBSCRIBE INFORMATION: > http://lists.ximian.com/mailman/listinfo/monodroid >
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