Fixed
Status Update
Comments
il...@google.com <il...@google.com>
cl...@google.com <cl...@google.com>
ap...@google.com <ap...@google.com> #2
A couple of questions:
1. Have you saw crash in real device or only in simulators?
2. Do you use dynamic feature for language ID?
1. Have you saw crash in real device or only in simulators?
2. Do you use dynamic feature for language ID?
fa...@hotmail.com <fa...@hotmail.com> #3
Tested on Android 12 Emulator with custom executor, but cannot repro this issue.
Description
Version used: 2.1.0-alpha01
Devices/Android versions reproduced on: API 28 emulator, Chrome OS
MediatorLiveData.addSource doesn't manually check for null source argument (annotation is there, which is good)
It's possible to accidentally add a null (or not yet initialized) source.
The issue is buried until the MediatorLiveData is observed, making it hard to find the original issue.
Best solution would be a quick check of the variables and fast fail before processing. e.g. assertNotNull(source)
- Sample project attached
relevant code:
private val mediatorLiveData = MediatorLiveData<Int>().apply {
// Here is the mistake, (allowed at compile time).
addSource(dataSource) { value = (it ?: 0) + 1 }
}
private val dataSource = MutableLiveData<Int>()
// This triggers the exception
mediatorLiveData.observe(this, Observer { // process })
Error output without check: (unhelpful unless you know the internals of MediatorLiveData)
2019-01-18 10:58:39.891 6385-6385/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.google.example.mediatorlatecheck, PID: 6385
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.lifecycle.LiveData.observeForever(androidx.lifecycle.Observer)' on a null object reference
at androidx.lifecycle.MediatorLiveData$Source.plug(MediatorLiveData.java:141)
at androidx.lifecycle.MediatorLiveData.onActive(MediatorLiveData.java:118)
at androidx.lifecycle.LiveData$ObserverWrapper.activeStateChanged(LiveData.java:436)
at androidx.lifecycle.LiveData$LifecycleBoundObserver.onStateChanged(LiveData.java:394)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:355)
at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:293)
at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:333)
at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:138)
at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:124)
at androidx.lifecycle.ReportFragment.dispatch(ReportFragment.java:123)
at androidx.lifecycle.ReportFragment.onStart(ReportFragment.java:83)
at android.app.Fragment.performStart(Fragment.java:2548)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1334)
at android.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1576)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1637)
at android.app.FragmentManagerImpl.dispatchMoveToState(FragmentManager.java:3046)
at android.app.FragmentManagerImpl.dispatchStart(FragmentManager.java:3003)
at android.app.FragmentController.dispatchStart(FragmentController.java:193)
at android.app.Activity.performStart(Activity.java:7165)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)