Changing listfragment content

Question

I use listfragment and try to change it's content. Here is my Activity code:

public class MainActivity extends Activity {
    public static Context appContext;
    public ToFragment ToFragment;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);     
        setContentView(R.layout.activity_main);
        ActionBar actionbar = getActionBar();
        actionbar.setDisplayShowTitleEnabled(false);
        actionbar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        ActionBar.Tab FromTab = actionbar.newTab().setText("FromFragment");
        ActionBar.Tab ToTab = actionbar.newTab().setText("ToFragment");

        FromFragment FromFragment = new FromFragment();
        ToFragment ToFragment = new ToFragment();

        ToTab.setTabListener(new MyTabsListener(ToFragment));
        FromTab.setTabListener(new MyTabsListener(FromFragment));

//        ListView tolistview = ToFragment.getListView();
//        ListView fromlistview = FromFragment.getListView();

        actionbar.addTab(ToTab);
        actionbar.addTab(FromTab);
    }

      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.mainmenu, menu);
        return true;
      }

      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.action_refresh:
            String[] countries = new String[] {
                    "Russia",
                    "USA",
                };  
            ToFragment.changeContent(countries);
          break;
        case R.id.action_settings:

          break;

        default:
          break;
        }

        return true;
      }
}

Here I initialize two listfragments, ToFragment and FromFragment. Then here (onCreateOptionsMenu) I try to change ToFragment's content via my function changeContent. Here is the code of Fragment:

public class ToFragment extends ListFragment {
    String[] countries = new String[] {
            "India",
            "Pakistan",
        };
    private LayoutInflater inflater;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        this.inflater = inflater;
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, countries);

        setListAdapter(adapter);

        return super.onCreateView(inflater, container, savedInstanceState);
    }

    public void changeContent(String[] array) {
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, array);
        setListAdapter(adapter);
    }

I tryed to make function changeContent work just like function onCreateView, as you see. But! My issue is that here it throws nullpointerexception and I'm really confused I can't realize what's the problem! Could you tell me what's wrong? Or could you advice better way to change listfragment content?

Here is error track:

04-08 22:48:33.292: I/System.out(8817): adapter == null
04-08 22:48:33.292: W/dalvikvm(8817): threadid=1: thread exiting with uncaught exception (group=0x414572d0)
04-08 22:48:33.297: E/AndroidRuntime(8817): FATAL EXCEPTION: main
04-08 22:48:33.297: E/AndroidRuntime(8817): java.lang.RuntimeException: Unable to start activity ComponentInfo{ru.rkarasev.miptrain/ru.rkarasev.miptrain.MainActivity}: java.lang.NullPointerException
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2355)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread.access$600(ActivityThread.java:151)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1335)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.os.Looper.loop(Looper.java:155)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread.main(ActivityThread.java:5493)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at java.lang.reflect.Method.invokeNative(Native Method)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at java.lang.reflect.Method.invoke(Method.java:511)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1028)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:795)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at dalvik.system.NativeStart.main(Native Method)
04-08 22:48:33.297: E/AndroidRuntime(8817): Caused by: java.lang.NullPointerException
04-08 22:48:33.297: E/AndroidRuntime(8817):     at ru.rkarasev.miptrain.ToFragment.changeContent(ToFragment.java:34)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at ru.rkarasev.miptrain.MainActivity.onCreate(MainActivity.java:49)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.Activity.performCreate(Activity.java:5066)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1101)
04-08 22:48:33.297: E/AndroidRuntime(8817):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2311)
04-08 22:48:33.297: E/AndroidRuntime(8817):     ... 11 more
04-08 22:48:35.382: D/Process(8817): killProcess, pid=8817
04-08 22:48:35.387: D/Process(8817): dalvik.system.VMStack.getThreadStackTrace(Native Method)
04-08 22:48:35.387: D/Process(8817): java.lang.Thread.getStackTrace(Thread.java:599)
04-08 22:48:35.387: D/Process(8817): android.os.Process.killProcess(Process.java:944)
04-08 22:48:35.392: D/Process(8817): com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:108)
04-08 22:48:35.392: D/Process(8817): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:693)
04-08 22:48:35.392: D/Process(8817): java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:690)
04-08 22:48:35.392: D/Process(8817): dalvik.system.NativeStart.main(Native Method)

score 0 · Answer 1 · edited May 23 '17 at 10:25

0

Change how you create your ArrayAdapter instance:

ArrayList<String> arrayList = new ArrayList<String>();
arrayList.addAll(Arrays.asList(countries));

ArrayAdapter<String> adapter = new ArrayAdapter<String>(inflater.getContext(), android.R.layout.simple_list_item_1, arrayList);

As found in this answer: Unable to modify ArrayAdapter in ListView: UnsupportedOperationException

public void changeContent(String[] array) {
    ArrayAdapter<String> adapter = (ArrayAdapter<String>)getListAdapter();
    if (adapter != null) {
        adapter.clear();
        adapter.addAll(Arrays.asList(array));
        adapter.notifyDataSetChanged();
    }
}

You don't need to recreate the adapter every time. Just clear and set the new array, then notify the adapter that the dataset has changed so your views will be updated.

edited May 23 '17 at 10:25

Community

1
1

answered Apr 08 '13 at 00:19

Brett Duncavage

2,163
14
16

Yes, I'm sure that adapter == null. How to get it? – user1933770 Apr 08 '13 at 05:06
Can you post the stack trace (add it to your question)? – Brett Duncavage Apr 08 '13 at 05:15
Seems like `changeContent` is getting called before SetListAdapter, which is weird. Try the update code with the adapter null check. – Brett Duncavage Apr 09 '13 at 00:03
I did. But how can I make sure that adapter was created? I mean, even with null check, for how long should I wait? – user1933770 Apr 09 '13 at 04:24
You still get that null reference even when checking for `if (adapter == ull)` in `changeContent()`? – Brett Duncavage Apr 09 '13 at 05:43
Now I get UnsupportedOperationException in line adapter.addAll(Arrays.asList(array)); – user1933770 Apr 09 '13 at 07:38

Changing listfragment content

1 Answers1