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We now have made sure that in all implementation of getTemplate(),  XXXTemplateBuilder.build() is returned; it will never explicitly returning a null. However,  this crash is still happening to our alpha/beta users.

We don't have reproduce steps.

getTemplate is annotated as @NonNull but unfortunately, this is not currently reflected in the reference documentation. We are working to fix that.

Rafa, can you please look at the log and see if there's anything else that we may be missing. We should not be crashing in this case, instead the error template should be displayed. If that's already happening, I don't believe there's anything to fix in the library beyond the documentation.

Hi, thank you very much for your response, but, please investigate this issue a bit further.
It is entirely my speculation that the cause of this crash is that getTemplate() could be returning null sometimes.

I would like to repeat what I said in the previous comment, we have now made sure that getTemplate() will never return null from our code, it is always "return XXXTemplateBuilder.build();", however, this is crash still happening a lot to our beta users. I'll provide with more logs on Monday.

Hi,
I have attached new logs for your reference.

Thank you for the new log, we'll look at it soon and get back to you.

Hi, yes, we are still seeing this crash happening to users using the new version where we have removed all the explicate return of "null" while using getTemplate().

All our use case of getTemplate() is now returning XXXBuilder.build().

We are not doing a null check on XXXBuilder.build(),  assuming it will never be null. Could that be null sometimes? Maybe we will add a null check before returning XXXBuilder.build() and returning an placeholderTemplate with error message when that happens.

Some more logs from yesterday if there is any help.

Hi,

Can you repro this bug locally?
> We don't have reproduce steps locally for this. We will let you know if we can manage to reproduce it consistently locally.

Does this happen on a specific Screen of yours, or on some, many, all?
> We don't know which screen this happens. We do see this crash happen very frequently among our beta users.

We use builder.build() in all the getTemplate() methods, can builder.build() ever return null? Do we need to do null check there and return a special screen?

In our code, we have  "getLifecycle().addObserver(this)" in all the screen constructors, like it is used in the sample apps, but, not doing removeObserver(this) anywhere. Could this be a problem? What is the best practice here? Is it necessary to do removeObserver? Perhaps in finalize()?

Are there any best practice on how the screen should be used that we perhaps missed?

Hope you have received the code Snippet I sent to N, if not, I can send to you directly.

Cheers!

Maybe a bit naive here, but, is it possibly to just do a null pointer check in your code?

Template template = XXX.getTemplate();

if (template !=null) {
 template.getClass()
} else {
 Log.E(TAG, "template should not be null")
}

Hi,  these following steps might help reproduce the issue:

Cheers!

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

commit 076857f2f01e8e30f8186cad44ce22192438073a
Author: Rafael Lima <therafael@google.com>
Date:   Thu Feb 25 23:28:48 2021

    Improvements to shutdown scenarios
   
    1. Do not send calls to app level callbacks if the app is not at least
    in created state
    2. Do not crash the app if the host is dead while trying to send an IPC
   
    Follow up review will stop dispatching calls from template related
    callbacks (i.e. onClick, etc)
   
    Relnote: "Improvements to not dispatch calls to app if its lifecycle is
    not at least in a created state"
    Test: Unit tests
    Bug:180530156
    Bug:179800224
    Bug:177921120
    Bug:178516889
   
    Change-Id: I8696503d1a9859411c4a52fa73d2852c8b3383d9

M       car/app/app-testing/src/main/java/androidx/car/app/testing/TestAppManager.java
M       car/app/app-testing/src/main/java/androidx/car/app/testing/TestCarContext.java
M       car/app/app-testing/src/main/java/androidx/car/app/testing/navigation/TestNavigationManager.java
M       car/app/app/src/main/java/androidx/car/app/AppManager.java
M       car/app/app/src/main/java/androidx/car/app/CarAppService.java
M       car/app/app/src/main/java/androidx/car/app/CarContext.java
M       car/app/app/src/main/java/androidx/car/app/HostDispatcher.java
M       car/app/app/src/main/java/androidx/car/app/ScreenManager.java
M       car/app/app/src/main/java/androidx/car/app/model/OnCheckedChangeDelegateImpl.java
M       car/app/app/src/main/java/androidx/car/app/model/OnClickDelegateImpl.java
M       car/app/app/src/main/java/androidx/car/app/model/OnItemVisibilityChangedDelegateImpl.java
M       car/app/app/src/main/java/androidx/car/app/model/OnSelectedDelegateImpl.java
M       car/app/app/src/main/java/androidx/car/app/model/SearchCallbackDelegateImpl.java
M       car/app/app/src/main/java/androidx/car/app/navigation/NavigationManager.java
M       car/app/app/src/main/java/androidx/car/app/utils/LogTags.java
M       car/app/app/src/main/java/androidx/car/app/utils/RemoteUtils.java
M       car/app/app/src/test/java/androidx/car/app/AppManagerTest.java
M       car/app/app/src/test/java/androidx/car/app/CarAppServiceTest.java
M       car/app/app/src/test/java/androidx/car/app/CarContextTest.java
M       car/app/app/src/test/java/androidx/car/app/HostDispatcherTest.java
M       car/app/app/src/test/java/androidx/car/app/navigation/NavigationManagerTest.java

https://android-review.googlesource.com/1607842