Koeber Koeber - 1 month ago 6
Android Question

Trying to remove fragment from view gives me NullPointerException on mNextAnim

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

Answer

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.