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

Use cases: Some phone(like OnePlus) will change the density when rotating the screen or enter PIP mode, I use slider to make a controller for a video player app, at this point the video is playing and the progress bar is changing, then App will be crashed

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

Not sure I understand the use case.

Slider cannot measure 0.dp it has to measure at least 2 thumbs so that the thumb can move from 0f to 1f. Do you mean to use Modifier.weight instead so that it takes the available space?

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

yes, i am using Modifier.weight for Slider, i don't know why it crash on OnePlus phone

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

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

Here is a example code of my slider controller

Row(Modifier.fillMaxWidth()) {
// Some icon buttons here

Slider(
    modifier = Modifier.weight(1f)
   //...
}

// Other icon buttons here
}

When exiting the horizontal screen state or entering the picture-in-picture mode, the above exception will be caused, and it only happens on OnePlus phone

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

Thanks I'll add a fix for parents with width 0.dp maybe it something that only happens briefly and then it measures something reasonable. Can you share the exact model/OS?

Issue 171125856