Fragment with Map crashes app when back button is pressed or when orientation changes

Question

I have an Activity that loads 2 tabs in the ActionBar. Tab 1 loads a Fragment that will will inflate a WebView, while Tab 2 loads a Fragment with a map. Initially, I have the problem of changing tabs that causes the app to crash. I have followed the instructions here and implemented onDestroyView().

The problem now is that if I press the back button from Tab 1 (WebView), it exits the Activity properly. But if I do it on Tab 2 (map), the app crashes. The exact same scenario applies to when I change the orientation. I am convinced that it has something to do with the onDestroyView(), but I am not sure what it is.

I have even attempted to Override the back button, but nothing works.

Here is my code to provide some context:

The Activity Class:

public class MyActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Displaying the tabs by calling ActionBar
    ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    //Details Tab
    String label1 = getResources().getString(R.string.details);
    Tab tab = actionBar.newTab();
    tab.setText(label1);
    TabListener<DetailsFragment> t1 = new TabListener<DetailsFragment>(this, label1, DetailsFragment.class);
    tab.setTabListener(t1);
    actionBar.addTab(tab);

    //Map Tab
    String label2 = getResources().getString(R.string.map);
    tab = actionBar.newTab();
    tab.setText(label2);
    TabListener<MapFragment> t2 = new TabListener<MapFragment>(this, label2, MapFragment.class);
    tab.setTabListener(t2);
    actionBar.addTab(tab);
}

private class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    /**
     * Constructor used each time a new tab is created.
     * 
     * @param activity
     *            The host Activity, used to instantiate the fragment
     * @param tag
     *            The identifier tag for the fragment
     * @param clz
     *            The fragment's Class, used to instantiate the fragment
     */
    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        // Check if the fragment is already initialized
        if (mFragment == null) {
            // If not, instantiate and add it to the activity
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            // If it exists, simply attach it in order to show it
            ft.attach(mFragment);

        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            // Detach the fragment, because another one is being attached
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // User selected the already selected tab. Usually do nothing.
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
} }

DetailsFragment:

public class DetailsFragment extends Fragment {


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View v = inflater.inflate(R.layout.morning, container, false);
    WebView webview = (WebView) v.findViewById(R.id.details);
    webview.loadUrl("file:///android_asset/pools/details.html");
    return v;
} }

MapFragment:

public class MapFragment extends Fragment {

static final LatLng mapLatLng = new LatLng("some numbers", "some numbers");
private GoogleMap map;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View v = inflater.inflate(R.layout.map, container, false);
    map = ((MapFragment)getFragmentManager().findFragmentById(R.id.map)).getMap();
    Marker amksc = map.addMarker(new MarkerOptions().position(mapLatLng).title("Map"));

    map.moveCamera(CameraUpdateFactory.newLatLngZoom(mapLatLng, 18)); 
    return v;
}


@Override
public void onDestroyView() {
    super.onDestroyView();
    MapFragment destroyMe = (MapFragment)getFragmentManager().findFragmentById(R.id.map);
    if (destroyMe != null) {
        getFragmentManager().beginTransaction().remove(destroyMe).commit();
    }
} }

Thanks for reading such a long post. Any help is greatly appreciated. I will be away for awhile without my laptop (15 days to be exact), so I may not be able to respond and test out your answer, but rest assured that I will =)

Thanks in advance!

EDITED to include Error Log (Not sure how to format it)

04-25 11:27:54.333: E/AndroidRuntime(21779): FATAL EXCEPTION: main

04-25 11:27:54.333: E/AndroidRuntime(21779): java.lang.NullPointerException

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1380)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.FragmentManagerImpl$1.run(FragmentManager.java:430)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Handler.handleCallback(Handler.java:615)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Handler.dispatchMessage(Handler.java:92)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.os.Looper.loop(Looper.java:213)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at android.app.ActivityThread.main(ActivityThread.java:4786)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at java.lang.reflect.Method.invokeNative(Native Method)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at java.lang.reflect.Method.invoke(Method.java:511)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)

04-25 11:27:54.333: E/AndroidRuntime(21779):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

it was work for me.. try it the below code write in the onDestory() method

@Override
    public void onDestroy() { 
if (fragment != null
                        && getFragmentManager().findFragmentById(
                                fragment.getId()) != null) {

                    getFragmentManager().beginTransaction().remove(fragment)
                            .commit();
                    fragment = null;
                }
}

Answer 2

I seem to have solved both the back button and orientation change problem.

The trick here is to not use onDestroyView(), but to change the way the fragments are handled. instead of ft.attach(mFragment) and ft.detach(mFragment), I changed them to ft.show(mFragment) and ft.hide(mFragment).

As for the orientation change causing the app to crash, I believe (do correct me if I am wrong) that as long as you do not have an alternative landscape layout, you can add android:configChanges="orientation|screenSize" to the manifest for this activity, like this:

<activity 
        android:theme="@style/AppTheme" 
        android:name="MyFragmentActivity" 
        android:label="@string/fragmentActivity" 
        android:configChanges="orientation|screenSize">
    </activity>

Answer 3

The GoogleMap needs a little bit of time to load, so it could return null if you want use it. Try moving this code in the onActivityCreated() method of your MapFragment

map = ((MapFragment)getFragmentManager().findFragmentById(R.id.map)).getMap();
Marker amksc = map.addMarker(new MarkerOptions().position(mapLatLng).title("Map"));

map.moveCamera(CameraUpdateFactory.newLatLngZoom(mapLatLng, 18)); 

That used to work for me. Be sure to check out the Fragment Lifecycle