Trying to remove fragment from view gives me NullPointerException on mNextAnim

Question

I've got 3 fragments, one NavigationDrawer, one MapFragment, and one user-defined "MapInfoFragment". I want the "MapInfoFragment" to appear semi-transparent over top of the MapFragment on certain events and disappear on others. I don't really care if I completely remove the fragment and create a new one each time, or I just change the visibility and information displayed. Currently I'm just trying to use FragmentManager's .hide() function, but I've also tried .remove and .detach with similar results.

Error:

03-18 14:28:10.965  24711-24711/com.[packageName].asTest D/AndroidRuntime﹕ Shutting down VM
03-18 14:28:10.965  24711-24711/com.[packageName].asTest E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.[packageName].asTest, PID: 24711
java.lang.NullPointerException: Attempt to write to field 'int android.app.Fragment.mNextAnim' on a null object reference
        at android.app.BackStackRecord.run(BackStackRecord.java:658)
        at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1447)
        at android.app.FragmentManagerImpl$1.run(FragmentManager.java:443)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5017)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)

Activity_main.xml:

<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.[packageName].asTest.MainActivity">

    <!-- As the main content view, the view below consumes the entire
         space available using match_parent in both dimensions. -->
    <FrameLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <fragment xmlns:android="http://schemas.android.com/apk/res/android"
            xmlns:map="http://schemas.android.com/apk/res-auto"
            android:id="@+id/map"
            android:name="com.google.android.gms.maps.MapFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            map:cameraZoom="8"
            map:mapType="satellite"
            map:uiRotateGestures="false"
            android:layout_gravity="center_horizontal|top"
        />
    </FrameLayout>

    <fragment android:id="@+id/navigation_drawer"
        android:layout_width="@dimen/navigation_drawer_width"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        android:name="com.[packageName].asTest.NavigationDrawerFragment"
        tools:layout="@layout/simple_list_item_1" />

    <fragment android:id="@+id/map_info"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:name="com.[packageName].asTest.MapInfoFragment" />




</android.support.v4.widget.DrawerLayout>

Offending Code:

FragmentTransaction ft = getFragmentManager().beginTransaction();
ft.hide(getFragmentManager().findFragmentById(R.id.map_info));
ft.commit();

Update 1

I changed map_info_layout to map_info and there's no change in the error I'm getting. I'd previously had map_info_layout defined as the id for the root FrameLayout of the MapInfoFragment's layout xml, so I think map_info_layout and map_info were pointing to the same thing.

Update 2: My solution

Turned out that I had MapInfoFragment extending android.support.v4.app.Fragment instead of android.app.Fragment and I was using the android.app.FragmentTransaction instead of android.support.v4.app.FragmentTransaction. Switched everything to android.app. since I'm not interested in older device compatibility. Thanks Fllo.

Update 3: General solution

Stop trying to hide null objects

Might be I'm wrong, but I don't see a fragment named `map_info_layout`, in your layout, I only see `map_info`. — Blo, Mar 18 '14 at 20:04

score 116 · Accepted Answer · answered May 20 '14 at 22:19

116

I know you've solved this yourself, but I want to explain how this error happens, since it just happened to me.

Basically you're calling hide(), remove(), etc., with a null value.

The error isn't obvious, and the stack trace doesn't originate from your own sources when this happens, so it's not trivial to realise what it is.

answered May 20 '14 at 22:19

gak

32,061
28
119
154

14

+ 1 for pointing this out. `Attempt to write to field 'int *.mNextAnim' on a null object reference` is raised when trying to show() or hide() passing a null fragment. F. – Flashbump Jan 23 '15 at 22:13
This should be the correct answer, lost so much time with this issue until I've found that: "Basically you're calling hide(), remove(), etc., with a null value." Thanks – GuilhE Jun 30 '15 at 11:25
2

I had to use `getFragmentManager().findFragmentById(R.id.faultyFragment)` instead of `getFragmentManager().findFragmentById(mReferenceToFaultyFragment.getId())`. I got the reference in `onCreateView()` – OneWorld Jul 02 '15 at 10:58

score 8 · Answer 2 · answered Feb 04 '16 at 13:39

8

It also happens when you call FragmentManager.popBackstack() without there being a fragment in the backstack.

answered Feb 04 '16 at 13:39

Christine

5,617
4
38
61

How did you solve it? I tried getBackStackEntryCount() and it did not work. – Ineta Dec 05 '16 at 08:48
I fixed it by not doing a popbackstack if there's no fragment in the backstack. – Christine Dec 05 '16 at 09:00
How exactly did you check for fragments in the backstack? I've tried fragmentManager.findFragmentById(CONTAINER_ID) != null and it did not work as well. Not sure what else to check. – Ineta Dec 05 '16 at 10:44
I don't check in the backstack. I just wrote my code so that it doesn't pop the backstack if there's no fragment in the backstack. I think generally it's a bad idea to pop the backstack if you don't know what's in it. – Christine Dec 05 '16 at 11:03
use `popBackStackImmediate()` instead – Desolator Mar 18 '18 at 05:56

score 4 · Answer 3 · answered Apr 03 '15 at 11:00

4

this is because you add or show or hide a fragment which is null now,try to check if it is null ,before you use it!

answered Apr 03 '15 at 11:00

howerknea

355
3
12

It happens to me before I can replace any fragment. It happens in `FragmentTransaction transaction = getActivity().getSupportFragmentManager().beginTransaction();` – Mr.Moustard Sep 29 '15 at 12:23

flobacca · Answer 4 · 2016-11-03T13:02:03.933

2

My problem was that FragmentManager's getFragments() sometimes returns a list where some fragments are null, and I was removing those null fragments.

edited Nov 03 '16 at 13:02

answered Nov 03 '16 at 04:46

flobacca

936
2
17
42

Seems to be my case, but I took fragments from ChildFragmentManager. Thanks! – Nikita Axyonov Apr 11 '17 at 12:28

score 0 · Answer 5 · answered Jun 02 '16 at 09:39

It happended to me only when from one of the fragments in the navigation drawer I showed a DialogFragment by using

newFragment.show(getFragmentManager(), "dialog");

If instead I used

newFragment.show(getChildFragmentManager(), "dialog");

this did not happened.

NOTE: The crash did not happen to me when showing or closing the dialog, but when changing to another fragment from the navigation drawer.

score 0 · Answer 6 · answered Nov 07 '16 at 14:22

Properly call show() and hide()...

    private void showFragment(int fragmentIndex, boolean addToBackStack) {
    FragmentManager fm = getFragmentManager();
    FragmentTransaction transaction = fm.beginTransaction();
    for (int i = 0; i < fragments.length; i++) {
        if (i == fragmentIndex) {
            transaction.show(fragments[i]);
        } else {
            transaction.hide(fragments[i]);
        }
    }
    if (addToBackStack) {
        transaction.addToBackStack(null);
    }
    transaction.commit();
}

score 0 · Answer 7 · answered Mar 29 '21 at 11:55

If you need to use getSupportFragmentManager(), in addition to doing a null check, you must also check to see if that fragment is currently added. If you only use a null, it will still crash. This will work:

if (fragment != null && fragment.isAdded()) {
                    getSupportFragmentManager().beginTransaction().
                            remove(getSupportFragmentManager().findFragmentById(R.id.fragment_container)).commit();
                }

Trying to remove fragment from view gives me NullPointerException on mNextAnim

Update 1

Update 2: My solution

Update 3: General solution

7 Answers7

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