NullPointerException: 'void android.app.Activity.runOnUiThread(java.lang.Runnable)' on a null object reference

[secondVISION]

Bug Report

Problem

What is expected to happen?

Cordova should silently exit.

What does actually happen?

Cordova crashes because the parent Activity is not alive anymore

Information

Start a CordovaWebview and load a slow/large website.

cordovaWebView.loadUrl(url)

If you return to the previous activity (by using the (hardware) back button), cordova will try to execute cordova.getActivity().runOnUiThread(), but the activity is no longer there.

e.g., https://github.com/apache/cordova-android/blob/master/framework/src/org/apache/cordova/CordovaWebViewImpl.java#L187

Stacktrace:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.runOnUiThread(java.lang.Runnable)' on a null object reference
        at org.apache.cordova.CordovaWebViewImpl$2.run(CordovaWebViewImpl.java:179)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:764)

Command or Code

See information above on how to reproduce.

Environment, Platform, Device

Android / All devices / All OS

Version information

Android Studio
Cordova 8.1.0

Checklist

• I searched for existing GitHub issues:
  Found issue: Application crash in CordovaWebViewImpl.java runOnUiThread #884 but this was closed due to lack of information
• I updated all Cordova tooling to most recent version:
  Crash occured on
  'org.apache.cordova:cordova:6.2.3'
  Updated to (crashed as well):
  'org.apache.cordova:framework:8.1.0'
• I included all the necessary information above

[jcesarmobile]

can you provide a sample app?

[jaeheonshim]

You should be able to replicate the problem by enabling the "Don't keep activities" option in Android Developer Options (Developer options => Apps => Don't keep activities (Destroy every activity as soon as the user leaves it.))

[breautek]

When doing that on the android simulator, I run into a different crash stacktrace

D/CordovaActivity: Paused the activity.
D/CordovaActivity: Stopped the activity.
D/CordovaActivity: CordovaActivity.onDestroy()
D/CordovaWebViewImpl: >>> loadUrl(about:blank)
W/cr_AwContents: WebView.destroy() called while WebView is still attached to window.
W/cr_AwContents: Application attempted to call on a destroyed WebView
    java.lang.Throwable
        at org.chromium.android_webview.AwContents.t(chromium-TrichromeWebViewGoogle.apk-stable-410404481:2)
        at Mt.loadingStateChanged(chromium-TrichromeWebViewGoogle.apk-stable-410404481:2)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:335)
        at android.os.Looper.loop(Looper.java:183)
        at android.app.ActivityThread.main(ActivityThread.java:7523)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:941)
E/chromium: [ERROR:aw_browser_terminator.cc(125)] Renderer process (5916) crash detected (code -1).

Maybe this depends on the API level of the device and/or the installed chrome version though. It kinda seems related.

[secondVISION]

Created a sample app: https://github.com/secondVISION/cordova-android-crash

How to reproduce:

• Click on "Start Cordova"
• Immediately press the Back key
• Wait on crash. Cordova will try to load the website in an activity which has already been destroyed.
  • Waiting can take up to 30 seconds I've noticed

Crash log:

2020-07-16 14:06:20.618 19256-19392/com.example.cordovacrash D/EGL_emulation: eglMakeCurrent: 0x8c152aa0: ver 3 0 (tinfo 0x8859b8c0)
2020-07-16 14:06:39.652 19256-19383/com.example.cordovacrash E/AndroidRuntime: FATAL EXCEPTION: pool-2-thread-1
    Process: com.example.cordovacrash, PID: 19256
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.Activity.runOnUiThread(java.lang.Runnable)' on a null object reference
        at org.apache.cordova.CordovaWebViewImpl$2.run(CordovaWebViewImpl.java:181)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
        at java.lang.Thread.run(Thread.java:764)
2020-07-16 14:06:39.819 19256-19310/com.example.cordovacrash D/EGL_emulation: eglMakeCurrent: 0xa1305300: ver 3 0 (tinfo 0xa13031f0)

[secondVISION]