[BaseTransientBottomBar] 1.1.0-rc01 causes View.invalidate(boolean) NullPointerException

[Naitbit]

Description:
After updating from Material 1.0.0 to 1.1.0-rc01 I saw multiple reports of crashes with BaseTransientBottomBar (and no app specific code in stacktrace).
Stacktraces look like:
Huawei Android 7

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.invalidate(boolean)' on a null object reference
       at android.view.View.setFlags + 11550(View.java:11550)
       at android.view.View.setVisibility + 8046(View.java:8046)
       at com.google.android.material.snackbar.BaseTransientBottomBar$9.run + 849(BaseTransientBottomBar.java:849)
       at android.os.Handler.handleCallback + 761(Handler.java:761)
       at android.os.Handler.dispatchMessage + 98(Handler.java:98)
       at android.os.Looper.loop + 156(Looper.java:156)
       at android.app.ActivityThread.main + 6617(ActivityThread.java:6617)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run + 942(ZygoteInit.java:942)
       at com.android.internal.os.ZygoteInit.main + 832(ZygoteInit.java:832)

Samsung Android 9

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.invalidate(boolean)' on a null object reference
       at android.view.View.setFlags + 15721(View.java:15721)
       at android.view.View.setVisibility + 10789(View.java:10789)
       at com.google.android.material.snackbar.BaseTransientBottomBar$9.run + 849(BaseTransientBottomBar.java:849)
       at android.os.Handler.handleCallback + 873(Handler.java:873)
       at android.os.Handler.dispatchMessage + 99(Handler.java:99)
       at android.os.Looper.loop + 214(Looper.java:214)
       at android.app.ActivityThread.main + 7094(ActivityThread.java:7094)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run + 494(RuntimeInit.java:494)
       at com.android.internal.os.ZygoteInit.main + 975(ZygoteInit.java:975)

Xiaomi Android 9

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.invalidate(boolean)' on a null object reference
       at android.view.View.setFlags + 14186(View.java:14186)
       at android.view.View.setVisibility + 10007(View.java:10007)
       at com.google.android.material.snackbar.BaseTransientBottomBar$9.run + 849(BaseTransientBottomBar.java:849)
       at android.os.Handler.handleCallback + 873(Handler.java:873)
       at android.os.Handler.dispatchMessage + 99(Handler.java:99)
       at android.os.Looper.loop + 201(Looper.java:201)
       at android.app.ActivityThread.main + 6823(ActivityThread.java:6823)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run + 547(RuntimeInit.java:547)
       at com.android.internal.os.ZygoteInit.main + 873(ZygoteInit.java:873)

LGE Android 9

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.invalidate(boolean)' on a null object reference
       at android.view.View.setFlags + 14222(View.java:14222)
       at android.view.View.setVisibility + 10027(View.java:10027)
       at com.google.android.material.snackbar.BaseTransientBottomBar$9.run + 849(BaseTransientBottomBar.java:849)
       at android.os.Handler.handleCallback + 873(Handler.java:873)
       at android.os.Handler.dispatchMessage + 99(Handler.java:99)
       at android.os.Looper.loop + 193(Looper.java:193)
       at android.app.ActivityThread.main + 6854(ActivityThread.java:6854)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run + 493(RuntimeInit.java:493)
       at com.android.internal.os.ZygoteInit.main + 860(ZygoteInit.java:860)

(if needed I can find few more stacktrace, but they seem to differ just by line numbers)

Expected behavior: BaseTransientBottomBar should not cause crashes/NPE

Steps to reproduce are unfortunately unknown, it seems to be relatively rare.
The issue did not happen in 1.0.0

Material Library version: 1.1.0-rc01

Device: Multiple Devices/Android OS versions affected.

[Naitbit]

Thanks for quick release.
I got report of

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.invalidate(boolean)' on a null object reference
       at android.view.View.setFlags + 13449(View.java:13449)
       at android.view.View.setVisibility + 9417(View.java:9417)
       at com.google.android.material.snackbar.BaseTransientBottomBar$9.run + 849(BaseTransientBottomBar.java:849)
       at android.os.Handler.handleCallback + 808(Handler.java:808)
       at android.os.Handler.dispatchMessage + 101(Handler.java:101)
       at android.os.Looper.loop + 166(Looper.java:166)
       at android.app.ActivityThread.main + 7425(ActivityThread.java:7425)
       at java.lang.reflect.Method.invoke(Method.java)
       at com.android.internal.os.Zygote$MethodAndArgsCaller.run + 245(Zygote.java:245)
       at com.android.internal.os.ZygoteInit.main + 921(ZygoteInit.java:921)

occurring with 1.1.0-rc02 so it seems like the issue was not resolved fully yet.
I'll follow up later whether the rate of occurrences was impacted a lot (not enough data yet to tell).

[Naitbit]

For now it impacted 20 users out of ~9000 . So the issue in 1.1.0-rc02 was not just one off case (occurrence rate seems to be lower then in 1.1.0-rc01 though due to low user count it may not be statistically significant).

[dsn5ft]

@Naitbit do you have any information about the scenario that causes the crash? Do you know if any activities are being created or destroyed while the Snackbar is being shown?

It looks like the NPE is internal to View.

[Naitbit]

@dsn5ft Sorry, I still don't have steps to reproduce, but with more reports it seems that what happens is:
Screen(fragment) is opened
Snackbar is called (likely twice, v.shortly after the screen is opened, probably via Snackbar.make(view, message, Snackbar.LENGTH_SHORT).show())
There was no device rotation in the meantime. Snackbar was called from main thread and activity was likely resumed , as it is was called from LiveData.observe.

That said I still did fail to reproduce it on any of my devices.

[Naitbit]

Further information:
I managed to artificially reproduce it.

Not sure if the view hierarchy is important for this bug, but I'm writing it down just in case:

The hierarchy was Activity>CoordinatorLayout as content>Fragment1
that after navigation tap switched to
Activity>CoordinatorLayout as content>Fragment2 with ViewPager that displayed > Fragment3 with viewPager > that displayed Fragment4
In my artificial way Fragment4 did call Snackbar immediately in onResume, then 2 frames later it did call Snackbar again which caused a crash. Snackbar used CoordinatorLayout from Activity as an container.

After throttling the calls to Snackbar I was no longer able to reproduce the issue. (worth noting that even with this convoluted setup it was reproducible on Huawei, but not reproducible on emulator nor Pixel - it is known to happen also at least on Samsung, LG, Xiamoi, Motorola Rockhip so maybe it requires different timing).

There seem to be no good reason to call Snackbar twice in such a short period though, so I'll change this in our app (and let you know if that was sufficient). (There is probably also no good enough reason for such a deep fragment hierarchy :D )

[Naitbit]

I can confirm that stopping app from displaying snackbar twice on consecutive frames did stop crashes.
(calling snackbar twice in a row on the same frame AFAIK did not crash).
We did fix the hierarchy later too, but that not displaying snackbar twice was sufficient to fix the issue.

[Naitbit]

(so I'm not sure if this needs fixing after all, but maybe there should be note somewhere in documentation to not spam Snackbar)

[wcshi]

The snackbarManager is supposed to handle multiple show() calls on the same snackbar.

material-components-android/lib/java/com/google/android/material/snackbar/SnackbarManager.java

Lines 76 to 84 in 7ef37a0

	if (isCurrentSnackbarLocked(callback)) {
	// Means that the callback is already in the queue. We'll just update the duration
	currentSnackbar.duration = duration;
	// If this is the Snackbar currently being shown, call re-schedule it's
	// timeout
	handler.removeCallbacksAndMessages(currentSnackbar);
	scheduleTimeoutLocked(currentSnackbar);
	return;