Realm Transaction in Xamarin

[dharamhbtik]

I am using Realm .Net SDK 11.0.0 with latest Xamarin forms framework

We are saving data to realm db and it is working fine but for few cases when call is coming from different threads or schedulers then it is throwing exception "can not modify ...... outside write transaction:
We have written extension method for adding the record . Something like below

1 public static T AddItem<T>(this Realm realm, T item)
2 {
3   if(realm.IsInTransaction){
4       realm.Add(item);
5 } else{
6 realm.Write(()=>{
7   realm.Add(item);
8 });
9 }
10 }

In the above code, it always go to line 4 as it finds IsIntransaction true and then throws exception
Cannot modify managed objects outside of a write transaction.

Here is stack trace

Thread started:  #49
[0:] Realms.Exceptions.RealmInvalidTransactionException: Cannot modify managed objects outside of a write transaction.
  at Realms.NativeException.ThrowIfNecessary () [0x00009] in D:\a\realm-dotnet\realm-dotnet\Realm\Realm\Native\NativeException.cs:77 
  at Realms.ObjectHandle.SetValue (System.String propertyName, Realms.Metadata metadata, Realms.RealmValue& value, Realms.Realm realm) [0x00148] in D:\a\realm-dotnet\realm-dotnet\Realm\Realm\Handles\ObjectHandle.cs:216 
  at Realms.ManagedAccessor.SetValue (System.String propertyName, Realms.RealmValue val) [0x00000] in D:\a\realm-dotnet\realm-dotnet\Realm\Realm\DatabaseTypes\Accessors\ManagedAccessor.cs:114 

[nirinchev]

Hm, I can see that we're not checking the thread in IsInTransaction, which may explain the issue that you're seeing. Essentially, what I believe is happening is:

1. You start a write transaction in thread A.
2. You call AddItem on thread B.
3. realm.IsInTransaction returns true.
4. On thread A, you commit/rollback the transaction.
5. On thread B, you're now trying to add an object outside of transaction.

While the error message is misleading, this wouldn't have worked in any case since you cannot access a Realm instance from multiple threads. So you should review your architecture and make sure to reopen the Realm instance on each thread/scheduler.

[dharamhbtik]

Make sense. Thank You