NullPointerException in PortalFragment; potential problems with Fragment-recreations

[fkirc]

Dear ionic-team,

After using Portals successfully in production for multiple weeks, I noticed hundreds of NullPointerExceptions in my sentry.io crash-reports. Specifically, a NullPointerException happened in the following line:
https://github.com/ionic-team/ionic-portals/blob/main/android/IonicPortals/src/main/kotlin/io/ionic/portals/PortalFragment.kt#L99

Here is the stacktrace that was reported by sentry.io:

java.lang.NullPointerException: null
at io.ionic.portals.PortalFragment.load(PortalFragment.kt:99)
at io.ionic.portals.PortalFragment.onViewCreated(PortalFragment.kt:44)
at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2987)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:502)
at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1435)
at android.app.Activity.performStart(Activity.java:8231)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3853)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:221)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:201)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:173)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:97)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2317)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8625)
at java.lang.reflect.Method.invoke(Method.java)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)

I suspect that this happens when a PortalFragment gets instantiated without an instance of the Portal-class.
For example, such erroneous instantiations might happen when the following empty default-constructor of a PortalFragment gets invoked:
https://github.com/ionic-team/ionic-portals/blob/main/android/IonicPortals/src/main/kotlin/io/ionic/portals/PortalFragment.kt#L27

This makes me question whether there is a potential problem with Fragment-recreations.
The Android-OS might destroy and recreate Fragments at any time, and this might trigger the NullPointerException.

Perhaps I could "fix" the bug by adding more null-checks to the problematic code, but my goal would be to find a root-cause instead of only adding null-checks.

[carlpoole]

Thanks for reporting, what version of Portals are you seeing the errors from?

[fkirc]

Previously, I was seeing those errors with 0.2.1.
However, today I deployed a production-update to 0.3.1, so I will monitor during the upcoming days whether the error still persists with 0.3.1.
From what I have seen, the relevant code-snippets in PortalFragment seem to be unchanged since 0.2.1.

[carlpoole]

Someone else reported NPE crashes that were similar that we made a fix for in #95 so I was curious if that might resolve it for you. That fix is in 0.3.1.

[fkirc]

Someone else reported NPE crashes that were similar that we made a fix for in #95 so I was curious if that might resolve it for you. That fix is in 0.3.1.

Yeah this seems like a related fix. I will let you know if something happens with 0.3.1, if nothing happens then I will close this issue within a week.

[fkirc]

Unfortunately I received the same stacktrace again with my new app-version, which means that the error is not fixed with 0.3.1.
I am thinking about forking to add some more null-checks, but perhaps it is necessary to rethink the PortalFragment-instantiation.

[fkirc]

Small sidenote: I embedded a PortalView into a larger RelativeLayout like this:

    <io.ionic.portals.PortalView
        app:portalId="MyPortalID"
        android:layout_below="@id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

So I instantiate Portals via XML-layouts, but not directly via Kotlin-code.
I still guess that the following empty-constructor leads to the crash:
https://github.com/ionic-team/ionic-portals/blob/main/android/IonicPortals/src/main/kotlin/io/ionic/portals/PortalFragment.kt#L27

[carlpoole]

Thanks for the feedback, I will take a look and see if I can pinpoint the cause.

[carlpoole]

I think I found the cause and pushed a fix. We will release this asap

[carlpoole]

Look out for Portals 0.4.1 - the fix is published! Thanks for reporting. Please let us know if you still encounter an issue

[fkirc]

Thank you for publishing a fix!
I will release an update of my app in the upcoming days, then I would notify you if there are still any issues.