Android app crashes when switching Fragment after showing a keyboard that is set with nextFocusDown

问题

I have an app that was working nicely with multiple fragments that are switching based on a navigation bar interaction. One of the screens has multiple text fields, and I decided to order these fields so the keyboard "next" would automatically take the user to the next fillable text field by using nextFocusDown. The last one leads to RadioGroup which results in the "done" button being shown.

The fields look like this (they are within LinearLayout that is within a NestedScrollView within another LinearLayout that is under the root FrameLayout):

<EditText
    android:id="@+id/firstName"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="textPersonName|textCapWords"
    android:nextFocusDown="@id/lastName"
    android:text="" />
<EditText
    android:id="@+id/lastName"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="textPersonName|textCapWords"
    android:nextFocusDown="@id/email"
    android:text="" />
<EditText
    android:id="@+id/email"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:ems="10"
    android:inputType="textEmailAddress"
    android:nextFocusDown="@id/localId"
    android:text="" />

There are many more fields, some include hints for text etc.

If I run the app, pick one field, and hit the "next" button until the keyboard disappears on its own - everything works well. The problem appears when I pick a field, the keyboard appears, and I hit the android down button that causes the keyboard to disappear. After doing so, everything within this screen looks good, and everything functions normally, until I switch a fragment, then the app crashes and I see in the logs these errors:

04-10 00:12:24.763 redacted E/AndroidRuntime: FATAL EXCEPTION: main
    Process: redacted, PID: 24660
    java.lang.NullPointerException: Attempt to invoke interface method 'void android.view.inputmethod.InputConnection.closeConnection()' on a null object reference
        at android.view.inputmethod.InputConnectionWrapper.closeConnection(InputConnectionWrapper.java:270)
        at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:541)
        at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:85)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
04-10 00:12:24.769 redacted E/UncaughtException: java.lang.NullPointerException: Attempt to invoke interface method 'void android.view.inputmethod.InputConnection.closeConnection()' on a null object reference
        at android.view.inputmethod.InputConnectionWrapper.closeConnection(InputConnectionWrapper.java:270)
        at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:541)
        at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:85)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6494)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

Any idea what's going on and how to avoid it?

P.S.
Since I am pretty sure it is related to the nextFocusOn and the keyboard, I didn't post more (it's a pretty big file), if you think anything is needed in addition, let me know, and I'll upload the relevant part.

回答1:

The thing that solved the issue for me was:

1. Clean the build (Build->Clean Project)
2. Exit Android Studio
3. Restart the android device
4. Start Android Studio (AFTER DEVICE STARTED)
5. Run

I have no idea why it solved the issue for me (I mostly write apps for iOS, and I never experienced bugs that require a device restart...). The weird thing is that I restarted the device, Android Studio, and clean the projects many times - so it appears the whole process has to be in that order...

回答2:

I faced with that bug today as well. I´m not sure if it will help in your case but it helped me. Based on answers in this topic: Android Studio 3.1 EditText StackOverflowError.

In my case it was enough just to disable advanced profiling

Run --> Edit Configuration --> Profiling Tab

In my case bug happen after changing conductor Controller from one with inputs to another. Error was exactly the same. And same as in related link i updated AS to 3.1.1 today.

回答3:

I had the same error using the Navigation from Android Architeture Components, which uses Fragment Transaction inside. The issue was that the EditText had text before the transaction and for some reason Android framework crashed.

The solution was setting all the EditText to null before doing the transaction.

回答4:

For zero reason, the above solutions didn't work. For zero reason, starting an emulator alongside my device and launching the app on both at once fixed the issue.

This doesn't make any sense and whoever did this crap owes me an hour.

I hope I can save someone's time if this fixes the issue.

来源：https://stackoverflow.com/questions/49745418/android-app-crashes-when-switching-fragment-after-showing-a-keyboard-that-is-set