Fixed
Status Update
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Comments
il...@google.com
cl...@google.com
ap...@google.com
If you need to add a custom Navigator but don't want to subclass NavHost (which we expect will be needed in most cases), the correct approach is to add it before you set your graph:
1) Don't use app:navGraph in your XML
2) Get a reference to your NavController
3) Add your Navigator to the NavController
4) Call setGraph on the NavController
This relies on the fact that NavController waits until the graph is set before restoring state / doing anything at all.
Technically, the createFragmentNavigator() call in NavHostFragment is already called at the same time as your proposed onNavControllerCreated() method so as a workaround, you could override that method, add your Navigator, then return super.createFragmentNavigator().
1) Don't use app:navGraph in your XML
2) Get a reference to your NavController
3) Add your Navigator to the NavController
4) Call setGraph on the NavController
This relies on the fact that NavController waits until the graph is set before restoring state / doing anything at all.
Technically, the createFragmentNavigator() call in NavHostFragment is already called at the same time as your proposed onNavControllerCreated() method so as a workaround, you could override that method, add your Navigator, then return super.createFragmentNavigator().
fa...@hotmail.com
The first solution does not work, because after screen rotation, the graph (probably a restored graph) is set when Activity.setContentView() is called.
The workaround with createFragmentNavigator() works, though it's not very elegant. Maybe the method could be renamed to createNavigators() and return a list or an array of Navigators?
Anyway, it is a good enough solution for now, so it is not very urgent.
In conclusion:
* I think that a better support for custom destinations should be provided before final release.
* I would suggest describing the "Add support for new destination types" section in the documentation in more details.
Thank you
The workaround with createFragmentNavigator() works, though it's not very elegant. Maybe the method could be renamed to createNavigators() and return a list or an array of Navigators?
Anyway, it is a good enough solution for now, so it is not very urgent.
In conclusion:
* I think that a better support for custom destinations should be provided before final release.
* I would suggest describing the "Add support for new destination types" section in the documentation in more details.
Thank you
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)