用户从 Google Play 下载时应用崩溃

Question

I have an app on Google Play with more than 45k download. The app has a bug with 3% users but cannot reproduce in debug or release mode. Very hard to reproduce. Anyone has experience with this bug please help me.

Crash log

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.sendAccessibilityEvent(int)' on a null object reference at android.view.ViewRootImpl$AccessibilityInteractionConnectionManager.onAccessibilityStateChanged(ViewRootImpl.java:7712) at android.view.accessibility.AccessibilityManager.lambda$-android_view_accessibility_AccessibilityManager_36305(AccessibilityManager.java:1007) at android.view.accessibility.-$Lambda$T3m_l9_RA18vCOcakSWp1lZCy5g$1.$m$0(Unknown Source:6) at android.view.accessibility.-$Lambda$T3m_l9_RA18vCOcakSWp1lZCy5g$1.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:789) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:172) at android.app.ActivityThread.main(ActivityThread.java:6637) at java.lang.reflect.Method.invoke(Method.java) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) at com.android.internal.os.ZygoteInit.main(ZygoteIni t.java:767)

Answer 1

One great thing about Android is that it is open source so you can work these things out for yourself.

First look at the the error message:

Attempt to invoke virtual method 'void android.view.View.sendAccessibilityEvent(int)' on a null object reference

This means there is some code somewhere doing foo.sendAccessibilityEvent(anInt) but foo is null (ie AKA a null object reference). It even tells you where this code is:

android.view.ViewRootImpl$AccessibilityInteractionConnectionManager.onAccessibilityStateChanged(ViewRootImpl.java:7712)

The next thing you need to do is look for the source code. You could do this in Android Studio or the web. I'll Google for "AccessibilityInteractionConnectionManager android source code"

The top link takes me to the code . I search in my web browser for the method name "onAccessibilityStateChanged()" in case the user has an old phone and the line number has changed.

The code looks like this:

 public void onAccessibilityStateChanged(boolean enabled) { if (enabled) { ensureConnection(); if (mAttachInfo.mHasWindowFocus) { mView.sendAccessibilityEvent(AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED); View focusedView = mView.findFocus(); if (focusedView != null && focusedView != mView) { focusedView.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_FOCUSED); }

As you can see, focusedView is checked for null, but mView isn't.

If we search for mview = in that file we see that it can happen in 3 ways:

• if the accessibility state changes before the object is initialized with a view. This looks possible unfortunately. I can't see any reason in the code while it wouldn't happen.
• in line 607, if a RemoteException occurs when the window is added to the display. If this happened you could see an "Adding window failed" RuntimeEception in your crashes. This is probably unlikely
• in line 3186, mView is set to null if dispatchDetachedFromWindow.

Anyway, it seems odd that 3% of your users are using AccessibilityManager and changing the state. Is it possible your app is using Accessibility to do stuff it shouldn't, and this is causing the crash. It might be that users on slower phones haven't initialized the view correctly before accessibility starts acting. You could try taking your uses of the Accessibility API out to see if that improves things.

Another possibility is that it isn't your app using accessibility, but another app trying manipulate your app. Is your app the kind of app where users might use accessibility services to cheat, eg a game which rewards clicking really quickly?