Unable to initialize NavBackStackEntry - IllegalStateException: Method addObserver must be called on the main thread [171125856]

Fixed

Bug

Status Update

No update yet.

Description

[Deleted User]

created issue #1

Oct 19, 2020 08:57AM

Component used: Navigation

Version used: 2.2.0, 2.3.0, 2.3.1

Devices/Android versions reproduced on: 10.0, 9.0 - probably not related

Description:

I've updated two dependencies in my project:

androidx.fragment:fragment 1.3.0-alpha06 -> 1.3.0-beta01
androidx.activity.activity 1.1.0 -> 1.2.0-beta01

and now I see that NavController::navigate needs to be called from the main thread. Otherwise NavBackStackEntry throws IllegalStateException when trying to register lifecycle observer.

Stacktrace:

Caused by: java.lang.IllegalStateException: Method addObserver must be called on the main thread
    at androidx.lifecycle.LifecycleRegistry.enforceMainThreadIfNeeded(LifecycleRegistry.java:317)
    at androidx.lifecycle.LifecycleRegistry.addObserver(LifecycleRegistry.java:172)
    at androidx.savedstate.SavedStateRegistryController.performRestore(SavedStateRegistryController.java:61)
    at androidx.navigation.NavBackStackEntry.<init>(NavBackStackEntry.java:84)
    at androidx.navigation.NavBackStackEntry.<init>(NavBackStackEntry.java:69)
    at androidx.navigation.NavController.navigate(NavController.java:970)
    at androidx.navigation.NavController.navigate(NavController.java:867)

There were no changes in documentation so I assume that this behavior is unintended.

Comments

il...@google.com <il...@google.com> #2Oct 19, 2020 08:10PM

This requirement for addObserver to be called on the main thread is part of the Lifecycle 2.3.0-alpha06 release notes, which Fragment/Activity depend on:

LifecycleRegistry now verifies that its methods are called on main thread. It was always a requirement for lifecycles of activities, fragments etc. An addition of observers from non-main threads resulted in hard to catch crashes in runtime.

It affects all APIs that use Lifecycle, including Navigation.

[Deleted User] <[Deleted User]> #3Oct 20, 2020 07:19AM

Thanks! Somehow I've missed that.

ap...@google.com <ap...@google.com> #4Apr 6, 2021 10:13PM

Project: platform/frameworks/support
Branch: androidx-main

commit 76230d4cbcf193ad3c01e2fb317a1bb3c571b1de
Author: Ian Lake <ilake@google.com>
Date: Tue Apr 06 12:53:25 2021

Mark navigate/setGraph as @MainThread

With the upgrade to Lifecycle 2.3.1,
Lifecycle now enforces that all creation and
changes to the Lifecycle state (including adding
and removing observers) should be done on the
main thread.

By marking navigate() and setGraph() as
`@MainThread`, we can give developeres better
visibility that these operations should only
be done on the main thread.

Relnote: "Navigation now depends on
[Lifecycle `2.3.1`](/jetpack/androidx/releases/lifecycle#2.3.1)
and now marks `setGraph()` and `navigate()`, the
methods that update the `NavBackStackEntry` `Lifecycle`,
as `@MainThread`, aligning Navigation with the main thread
enforcement introduced in Lifecycle `2.3.0`."
Test: existing and updated tests pass
BUG: 171125856

Change-Id: Ifcbe407d9cb186b50f05cbbd8bc5e11e19115a82

M navigation/navigation-dynamic-features-fragment/src/androidTest/java/androidx/navigation/dynamicfeatures/fragment/DynamicNavHostFragmentTest.kt
M navigation/navigation-runtime/api/current.txt
M navigation/navigation-runtime/api/public_plus_experimental_current.txt
M navigation/navigation-runtime/api/restricted_current.txt
M navigation/navigation-runtime/build.gradle
M navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt

https://android-review.googlesource.com/1665821

il...@google.com <il...@google.com> #5Apr 6, 2021 10:17PM

Marked as fixed, reassigned to il...@google.com.

For the upcoming Navigation 2.4.0-alpha01 release, we've made it explicit that setGraph() and navigate() should only be called on the main thread (by adding @MainThread annotations to the methods), thus aligning with the main thread enforcement of Lifecycle 2.3.

ap...@google.com <ap...@google.com> #6Apr 12, 2021 11:58PM

Project: platform/frameworks/support
Branch: androidx-main

commit 00c608a86c44b066198bd8c1dc7e2aef6088d4e1
Author: Ian Lake <ilake@google.com>
Date: Mon Apr 12 14:04:54 2021

Mark popBackStack and navigateUp as @MainThread

In addition to the navigate() and setGraph()
methods updated in

https://android-review.googlesource.com/1665821
the methods for popping the back stack
should also be marked as @MainThread.

Relnote: "Navigation now depends on
[Lifecycle `2.3.1`](/jetpack/androidx/releases/lifecycle#2.3.1)
and now marks all of the methods that update the
`NavBackStackEntry` `Lifecycle`, including `setGraph()`,
`navigate()`, `popBackStack()`, and `navigateUp()`,
as `@MainThread`, aligning Navigation with the main thread
enforcement introduced in Lifecycle `2.3.0`."
Test: existing and updated tests pass
BUG: 171125856

Change-Id: Ib8bedbb3fe384b28c7441cbd57a0751eba307a2b

M navigation/navigation-runtime/api/current.txt
M navigation/navigation-runtime/api/public_plus_experimental_current.txt
M navigation/navigation-runtime/api/restricted_current.txt
M navigation/navigation-runtime/src/main/java/androidx/navigation/NavController.kt

https://android-review.googlesource.com/1673448

Issue 171125856