[Android] NullReferenceException on pause/resume before init

We are seeing a handful amount of exceptions in cloud diagnostic on android after update to core package version 2.2.1 and plugin version 2.2.5 and still present at versions 2.2.2 core and 2.2.7 plugin. Exception occurs if user minimizes and restores app before UnityPurchasing.Initialize call was made. Due to delayed initialization it's easy to reproduce in our app

Spoiler: Stacktrace

NullReferenceException: Object reference not set to an instance of an object.

Managed Stack Trace:

UnityEngine.Purchasing.ReflectionUtils.HasMethodInInterface (System.Object objectToCheck, System.String methodName) (at <00000000000000000000000000000000>:0)
UnityEngine.Purchasing.GoogleFetchPurchases.OnFetchedPurchaseSuccessful (System.Collections.Generic.List`1[T] purchases, System.Boolean shouldReturnNonAcknowledgedPurchases) (at <00000000000000000000000000000000>:0)
UnityEngine.Purchasing.GoogleFetchPurchases+<>c__DisplayClass6_0.<FetchPurchases>b__0 (System.Collections.Generic.List`1[T] purchases) (at <00000000000000000000000000000000>:0)
System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
UnityEngine.Purchasing.Extension.UnityUtil.OnApplicationPause (System.Boolean paused) (at <00000000000000000000000000000000>:0)

 

We can reproduce this too. Use switch the app to background before UnityPurchasing.Initialize has been made. It looks like Unity wants to call an interface method which is not yet set (as the app was paused before unity was completely initialised). Unity 2019.4.19f1, newest inapp package (store and service)

 

1. Start the app and wait until the launch screen appears
2. Swipe up from the bottom to put the app in background (keep it in background for 10 seconds or so)
3. Bring it to foreground again
4. The exception is logged
5. We start initializing Unity IAP

I think that the OnApplicationPause handler from Unity IAP tries to call an interface method of the class object set when initializing unity with the builder. But this didn't happen yet at the time yet.

We experience a lot of this logs in unity analytics and are pretty sure this happens while facebook initializes and shows the login window and thus switches the app to background. (which happens before unity IAP is initialized)

Code (CSharp):

1. UnityEngine.Purchasing.ReflectionUtils.HasMethodInInterface (System.Object objectToCheck, System.String methodName) (at <00000000000000000000000000000000>:0)
2. UnityEngine.Purchasing.GoogleFetchPurchases.OnFetchedPurchase (System.Collections.Generic.List`1[T] purchases) (at <00000000000000000000000000000000>:0)
3. System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
4. System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
5. System.Action`1[T].Invoke (T obj) (at <00000000000000000000000000000000>:0)
6. UnityEngine.Purchasing.GooglePlayStoreService.DequeueFetchPurchases () (at <00000000000000000000000000000000>:0)
7. System.Action.Invoke () (at <00000000000000000000000000000000>:0)
8. System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <00000000000000000000000000000000>:0)
9. UnityEngine.AndroidJavaProxy.Invoke (System.String methodName, System.Object[] args) (at <00000000000000000000000000000000>:0)
10. UnityEngine._AndroidJNIHelper.InvokeJavaProxyMethod (UnityEngine.AndroidJavaProxy proxy, System.IntPtr jmethodName, System.IntPtr jargs) (at <00000000000000000000000000000000>:0)
11. Rethrow as TargetInvocationException: UnityEngine.Purchasing.BillingClientStateListener.onBillingSetupFinished(UnityEngine.AndroidJavaObject)
12. UnityEngine.AndroidJavaProxy.Invoke (System.String methodName, System.Object[] args) (at <00000000000000000000000000000000>:0)
13. UnityEngine._AndroidJNIHelper.InvokeJavaProxyMethod (UnityEngine.AndroidJavaProxy proxy, System.IntPtr jmethodName, System.IntPtr jargs) (at <00000000000000000000000000000000>:0)

Happens on various Android version from 5.0 up to 10.x

 

No, its not codeless, everything is done manually (like we do for years already).

But basically, I think it's rather simple to reproduce and not dependent on any Unity IAP usage code. The exception happens before we even call a single Unity IAP function.

As said, it looks like that when Unity resumes, Unity IAP calls a IStoreListener function on the class provided by UnityPurchasing.Initialize(). But this has not been called yet. (We don't call it in awake but later when the user logged in)

If your sample code initialises Unity IAP in Awake() already I'm pretty sure you cannot reproduce this. Just don't initialise it and make sure Unity IAP calls UnityEngine.Purchasing.GoogleFetchPurchases.OnFetchedPurchase internally when the app is paused/resume. (not sure when this is called, maybe when purchases have been made already earlier)

We made a 1% staged rollout to 10.000 new users and receive this exception on approx. 7.000 new users (the unique situation with new users is that the app switches to Facebook for the login process, thus pausing the app. When resuming, BEFORE Unity IAP is initialised from us, Unity IAP tries to call a IStoreListener interface function on a null object (because it has not been set yet)

If you take a look into the code of UnityEngine.Purchasing.ReflectionUtils.HasMethodInInterface I'm pretty sure it tries to call a method on the class which will be set LATER with UnityPurchasing.Initialize() and doesn't check if it is null

 

No problem at all, but as said, even without any single Unity IAP code in our app (only the package and library added, no custom code), this happens. Just see this as a heads up, as its no crash we can simply ignore this for the time being

 

I'm pretty sure others will report this too in near future, so I will just wait for a fix

 

Just a last appendix which might help hunting this down, this didn't happen with any Unity InApp version up to including core 2.2.1 and in-app 2.2.5

 

No, its fine, we just simply hoped to take a quick look into the code and see, yeah, there is the possibility that we call an interface method on the not yet store IStoreListener. (there is no need to work with the sample project as it happens with zero code too). Just thought Unity is interested in getting valuable detailed reports...

 

But, we made it even simpler.

Fresh Unity 2019.4.19f1 project, add in-app package, enable in-app in service window. Build, Download,Pause, Resume -> Exception logged (not a single line of Unity IAP code from our side). So, this is the reason I'm not sure what the Sample IAP Project should change, and even if it works, a plain empty project with 2.2.7 does not...

If we ever have a bit of spare time I will download the sample IAP project and send the log, but this could take a while...

Our post here was really just meant to make you aware of an issue (we are not the only ones having this), not to get it fixed for us quickly...

 

Affected versions and devices: https://pasteboard.co/JQb0pAE.png

 

Sorry for being silent in this thread, issue seems to be unharmful for our users therefore has low priority. Anyway described case was indeed happening in our app - StandarPurchasingModule was created almost at startup and UnityPurchasing.Initialize call was made like 5-8 seconds later. Issue is resolved after some code rearragement, atleast on my device. We will deploy this fix soon and i will post an update. Thanks everyone for helping with this issue

 

In our new release this error is completely gone, thanks everyone once again