Structure
(names of Activies/Fragments changed)
Based on some advice written in Android Programming: The Big Nerd Ranch Guide, I have the following structure:
MyListFragment extends ListFragment
MyListActivity extends SimpleFragmentActivity
SimpleFragmentActivity extends ActionBarActivity
MyListActivity.java
public class MyListActivity extends SingleFragmentActivity {
@Override
protected Fragment createFragment() {
return new MyListFragment();
}
}
SingleFragmentActivity.java
public abstract class SingleFragmentActivity extends ActionBarActivity {
protected abstract Fragment createFragment ();
@Override
public void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fragment);
FragmentManager fm = getSupportFragmentManager();
Fragment fragment = fm.findFragmentById(R.id.fragmentContainer);
if (fragment == null) {
fragment = createFragment();
fm.beginTransaction().add(R.id.fragmentContainer, fragment).commit();
}
}
}
After having outlined and programmed the basic functionality of my app (including Contextual Action Bar, navigation, …) I wanted to make sure that the app is as backwards compatible as possible without too much additional effort. Therefore, I started using the AppCompat (com.android.support:appcompat-v7:20+) ActionBar.
What baffled me right at the beginning was that—opposed to every tutorial or Android’s Developer guidelines I read—the getSupportActionBar method has never been available in Android Studio (I’m using Android Studio v0.8.2 and JRE 1.7_60). Whenever I type getActivity().getSup
, the only suggestions I get are getSupportFragmentManager
and getSupportLoaderManager
.
As a workaround, I create a member variable ActionBar mActionBar
in MyListFragment
and initialise it:
@Override
public void onAttach (Activity activity) {
super.onAttach(activity);
mActionBar = ((ActionBarActivity) activity).getSupportActionBar();
}
That seemed to do the trick on either Android 4.4.4 (Moto G) and 2.3.4 (LG E-510)—the only devices I have available.
However—coming to the problem I have—on rotation the ActionBar assignment gets lost and the application crashes with a NullPointerException. Debugging the application and setting a breakpoint on the following line in onCreate
:
mActionBar.setTitle(R.string.title_activity_my_list);
I found out that mActionBar is null after the rotation. Placing said line in onCreateView
didn’t help.
What I tried
mActionBar
in
onAttach
onActivityCreated
onCreate
/onCreateView
right before .setTitle gets calledI’m out of ideas here and grateful for advice.
EDIT-0 (30.07.)
Exception being thrown (after editing according to Alex’ suggestion)
07-30 15:05:25.239 5049-5049/MYAPPNAME E/AndroidRuntime﹕ [Blue Error Handler] Make Debugging Report file for main
java.lang.RuntimeException: Unable to start activity ComponentInfo{MYAPPNAME/MYAPPNAME.MYLISTACTIVITY}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1653)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1669)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:2838)
at android.app.ActivityThread.access$1600(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3737)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:894)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at MYAPPNAME.MYLISTFRAGMENT.onCreate(MYLISTFRAGMENT.java:54)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1481)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:908)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1103)
at android.support.v4.app.FragmentManagerImpl.dispatchCreate(FragmentManager.java:1896)
at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:216)
at android.support.v7.app.ActionBarActivity.onCreate(ActionBarActivity.java:98)
at MYAPPNAME.SingleFragmentActivity.onCreate(SingleFragmentActivity.java:22)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1617)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1669)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:2838)
at android.app.ActivityThread.access$1600(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3737)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:894)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:652)
at dalvik.system.NativeStart.main(Native Method)
MyListFragment
line 54 (exception occured using either SingleFragmentActivity and ActionBarActivity as a cast)
((SingleFragmentActivity) getActivity()).getSupportActionBar().setTitle(R.string
.title_activity_my_list);
SingleFragmentActivity
lines 20-22:
@Override
public void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Cast your getActivity()
to ActionBarActivity
/AppCompatActivity
(depends what you are using) and you will have access to the support ActionBar
.
((AppCompatActivity)getActivity()).getSupportActionBar();
or
((ActionBarActivity)getActivity()).getSupportActionBar();
Use this code in onActivityCreated(...)
method instead of onAttach(...)