android - 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.