MediatorLiveData.addSource should check for null [123085232]

Fixed

Bug

androidx-ui-starter-projects

Status Update

No update yet.

Description

ke...@google.com

created issue #1

Jan 18, 2019 08:07PM

Component used: MediatorLiveData
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)

MediatorLateCheck.zip

274 KB

Download

Comments

il...@google.com <il...@google.com> Nov 18, 2021 10:12PM

Status: New

cl...@google.com <cl...@google.com> Apr 14, 2022 11:08PM

Assigned to cl...@google.com.

ap...@google.com <ap...@google.com> #2Apr 19, 2022 05:51PM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-master-dev

commit fb1c82582399043b149eb2630f524c75de9c88dc
Author: Jelle Fresen <jellefresen@google.com>
Date: Thu Aug 15 11:34:36 2019

Disallow intercept, touch slop and canScroll in nestedPreScroll

* Disallow intercept (requestDisallowInterceptTouchEvent(true))
When scroll delta is consumed by dispatchNestedPreScroll, the parent
should be requested not to intercept subsequent touch events, just as
when scroll is consumed by the widget itself or dispatchNestedScroll.

* Touch slop
NestedScrollingChild implementations should only call
dispatchNestedPreScroll after the delta x/y has exceeded the touch slop.

* canScroll (canScrollHorizontally/canScrollVertically)
The dx/dy values passed to dispatchNestedPreScroll should be zero if the
child can't scroll in that direction.

Fixed in:
- RecyclerView
- NestedScrollView

Bug: 138668210
Bug: 139530818
Test: ./gradlew connectedCheck
Change-Id: I85b327ad096fbbd204adb92f630770ec7fad5990

M core/core/src/androidTest/java/androidx/core/widget/NestedScrollViewNestedScrollingChildTest.java
M core/core/src/main/java/androidx/core/widget/NestedScrollView.java
M recyclerview/recyclerview/src/androidTest/java/androidx/recyclerview/widget/RecyclerViewNestedScrolling3RequestDisallowInterceptTouchTest.java
M recyclerview/recyclerview/src/androidTest/java/androidx/recyclerview/widget/RecyclerViewNestedScrollingChildTest.java
M recyclerview/recyclerview/src/main/java/androidx/recyclerview/widget/RecyclerView.java

https://android-review.googlesource.com/1105373

https://goto.google.com/android-sha1/fb1c82582399043b149eb2630f524c75de9c88dc

IssueTracker