NullPointerException，同时恢复活动

Question

I am getting this crash on a Nexus device (a Sony one with the same OS version does not crash):

02-20 14:38:14.551 22255 22255 I DebugActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'android.os.Handler android.support.v4.app.FragmentHostCallback.getHandler()' on a null object reference
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.support.v4.app.FragmentManagerImpl.ensureExecReady(FragmentManager.java:2180)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2233)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:379)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.support.v4.app.FragmentActivity.onResume(FragmentActivity.java:461)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at com.whatever.sdk.MyActivity.onResume(MyActivity.java:109)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at com.whatever.sdk.MyActivity$1.onCallStateChanged(MyActivity.java:231)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.telephony.PhoneStateListener$2.handleMessage(PhoneStateListener.java:295)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.os.Handler.dispatchMessage(Handler.java:102)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.os.Looper.loop(Looper.java:148)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at android.app.ActivityThread.main(ActivityThread.java:5417)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at java.lang.reflect.Method.invoke(Native Method)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
02-20 14:38:14.551 22255 22255 I DebugActivity:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

And here is the relevant piece of code:

public class MyActivity extends AppCompatActivity {
...
    private final PhoneStateListener phoneStateListener = new PhoneStateListener() {
        @Override
        public void onCallStateChanged(int state, String incomingNumber) {
            if(state == TelephonyManager.CALL_STATE_IDLE) {
                MyActivity.this.onResume();
...
    @Override
    protected void onResume() {
        try {
            super.onResume();
...

The activity is not declared with any launchMode and trying to add different flags such as Intent.FLAG_ACTIVITY_CLEAR_TOP when starting the activity did not help. We have supportLibraryVersion = '27.0.2'

Is there an obvious fix to this and why is it happening on some devices and not on others?

Answer 1

Instead of calling Android lifecycle method like onResume() in onCallStateChanged() just remove the relevant code of onResume() in a separate method and call that method from onCallStateChanged() . That way when the Activity will resume the relevant code gets called and also when needed you can call that method to run the relevant code. Ofcourse you will need to add appropriate object condition checking in this newly created method.

Answer 2

From the error log I can see you are working with Fragments. I have encountered similar error before. One other thing comes to mind is saving a reference to your MainActivity eg in Fragments in a reference like Activity mainActivityRef = getActivity() . Later try to use this as mainActivityRef.onMyFunc() . This has saved me from this error Attempt to invoke virtual method 'android.os.Handler android.support.v4.app.FragmentHostCallback.getHandler()' on a null object reference

Answer 3

Credit to @ben-p's comment for the undocumented info on "only the Android framework should call [onResume()]" (mind you, this is a public method, along with onPostResume ), the solution was to remove phoneStateListener . Testing on the emulator, it is clear that the activity (and the video it hosts) is correctly paused and resumed by the framework when an incoming call notification is received and when the notification is dismissed or when the user finishes the phone call. The confusing part is that on most devices, calling onResume() directly does not lead to a crash, hiding the bug.