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

Answer 1

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.

Answer 2

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