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POAndroid: NullPointerException in my Fragment using BackStack
 

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  1. POAndroid: NullPointerException in my Fragment using BackStack
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    <p>I use the Master Detail fragment in Android. I have a ItemListActivity which responds to a callback in a ItemListFragment. If a item in the ListFragment is clicked a callback in the activity is fired. It is then decided if a smartphone or a tablet is used and depending on that new activity/fragment is created. </p> <p>The problem occurs using smartphones: A click on a item in the ItemListFragment, starts a new ItemDetailActivity with a ItemDetailFragment. I want to navigate with the Up Navigation in the ActionBar back to the ItemListFragment but I receive a NullPointerException:</p> <p>My ItemListFragment: </p> <pre><code>@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d("debug","Hallo in ItemListFragment"); //show ActionBar setHasOptionsMenu(true); //get reference to activity myApp = getActivity().getApplication(); feed = (RSSFeed) getActivity().getIntent().getExtras().get("feed"); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { //inflate the fragment with the custom detail fragment View view = inflater.inflate(R.layout.feed_list, null); return view; } @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); //get listview from layout lv = getListView(); lv.setVerticalFadingEdgeEnabled(true); // Set custom list adapter to the ListView adapter = new CustomListAdapter(getActivity(), feed); lv.setAdapter(adapter); } //Inflate ActionBar @Override public void onCreateOptionsMenu(Menu optionsMenu, MenuInflater inflater) { inflater.inflate(R.menu.main, optionsMenu); } @Override public void onViewCreated(View view, Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); // Restore the previously serialized activated item position. if (savedInstanceState != null &amp;&amp; savedInstanceState.containsKey(STATE_ACTIVATED_POSITION)) { setActivatedPosition(savedInstanceState.getInt(STATE_ACTIVATED_POSITION)); } } @Override public void onAttach(Activity activity) { super.onAttach(activity); // Activities containing this fragment must implement its callbacks. if (!(activity instanceof Callbacks)) { throw new IllegalStateException("Activity must implement fragment's callbacks."); } mCallbacks = (Callbacks) activity; } @Override public void onDetach() { super.onDetach(); // Reset the active callbacks interface to the dummy implementation. mCallbacks = sDummyCallbacks; } @Override public void onListItemClick(ListView listView, View view, int position, long id) { super.onListItemClick(listView, view, position, id); // Notify the active callbacks interface (the activity, if the // fragment is attached to one) that an item has been selected. if (mCallbacks != null) { Log.d("debug","Callback in ItemListFragment mit Position: "+position+"und Feed: "+feed); mCallbacks.onItemSelected(position, feed); } } @Override public void onSaveInstanceState(Bundle outState) { super.onSaveInstanceState(outState); if (mActivatedPosition != ListView.INVALID_POSITION) { // Serialize and persist the activated item position. outState.putInt(STATE_ACTIVATED_POSITION, mActivatedPosition); } } /** * Turns on activate-on-click mode. When this mode is on, list items will be * given the 'activated' state when touched. */ public void setActivateOnItemClick(boolean activateOnItemClick) { // When setting CHOICE_MODE_SINGLE, ListView will automatically // give items the 'activated' state when touched. getListView().setChoiceMode(activateOnItemClick ? ListView.CHOICE_MODE_SINGLE : ListView.CHOICE_MODE_NONE); } private void setActivatedPosition(int position) { if (position == ListView.INVALID_POSITION) { getListView().setItemChecked(mActivatedPosition, false); } else { getListView().setItemChecked(position, true); } mActivatedPosition = position; } //OnClick auf ActionBar @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: return true; case R.id.refresh_option: refreshList(item); return true; } return super.onOptionsItemSelected(item); } //Click on refresh in ActionBar -&gt; Refresh the List public void refreshList(final MenuItem item) { /* Attach a rotating ImageView to the refresh item as an ActionView */ LayoutInflater inflater = (LayoutInflater) getActivity().getApplication() .getSystemService(Context.LAYOUT_INFLATER_SERVICE); ImageView iv = (ImageView) inflater.inflate(R.layout.action_refresh, null); Animation rotation = AnimationUtils.loadAnimation(getActivity(), R.anim.refresh_rotate); rotation.setRepeatCount(Animation.INFINITE); iv.startAnimation(rotation); item.setActionView(iv); // trigger feed refresh: Thread thread = new Thread(new Runnable() { @Override public void run() { DOMParser tmpDOMParser = new DOMParser(); feed = tmpDOMParser.parseXml("http://www.androidcentral.com/feed"); Log.d("debug", "Refresh Liste mit Feed: "+feed); ItemListFragment.this.getActivity().runOnUiThread(new Runnable() { @Override public void run() { if (feed != null &amp;&amp; feed.getItemCount() &gt; 0) { Log.d("debug", "Aktualisiere Liste"); adapter.notifyDataSetChanged(); lv.setAdapter(adapter); item.getActionView().clearAnimation(); item.setActionView(null); } } }); } }); thread.start(); } @Override public void onDestroy() { super.onDestroy(); adapter.imageLoader.clearCache(); adapter.notifyDataSetChanged(); } </code></pre> <p>My ItemListActivity:</p> <pre><code>public class ItemListActivity extends FragmentActivity implements ItemListFragment.Callbacks { /** * Whether or not the activity is in two-pane mode, i.e. running on a tablet * device. */ private boolean mTwoPane; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d("debug","Hallo in der ItemListActivity"); //load static ItemListFragment in single pane //in two pane load also ItemListFragment static and //add item_detail_container in activity_item_detail setContentView(R.layout.activity_item_list); if (findViewById(R.id.item_detail_container) != null) { // The detail container view will be present only in the // large-screen layouts (res/values-large and // res/values-sw600dp). If this view is present, then the // activity should be in two-pane mode. mTwoPane = true; // In two-pane mode, list items should be given the // 'activated' state when touched. //TODO aktivierte Listelement anzeigen ((ItemListFragment) getSupportFragmentManager() .findFragmentById(R.id.item_list)) .setActivateOnItemClick(true); } } /** * Inflate ActionBar */ public void onCreateOptionsMenu( Menu menu, MenuInflater inflater) { inflater.inflate(R.menu.main, menu); } /** * Callback method from {@link ItemListFragment.Callbacks} * indicating that the item with the given ID was selected. */ @Override public void onItemSelected(int id, RSSFeed feed) { if (mTwoPane) { // In two-pane mode, show the detail view in this activity by // adding or replacing the detail fragment using a // fragment transaction. Log.d("debug","TwoPane Modus: Callback Methode in der ItemListActivity " + "mit Position: "+id+"und Feed: "+feed); Bundle arguments = new Bundle(); arguments.putSerializable("feed", feed); arguments.putInt("pos", id); //arguments.putLong(ItemDetailFragment.ARG_ITEM_ID, id); ItemDetailFragment fragment = new ItemDetailFragment(); fragment.setArguments(arguments); getSupportFragmentManager().beginTransaction() .replace(R.id.item_detail_container, fragment) .addToBackStack(null) .commit(); } else { // In single-pane mode, simply start the detail activity for the selected item ID. Log.d("debug","SinglePane Modus: Callback Methode in der ItemListActivity"); Intent detailIntent = new Intent(this, ItemDetailActivity.class); detailIntent.putExtra("pos", id); detailIntent.putExtra("feed", feed); startActivity(detailIntent); } } </code></pre> <p>MyItemDetaiFragment:</p> <pre><code>public class ItemDetailFragment extends Fragment{ private int fPos; RSSFeed fFeed; private ShareActionProvider mShareActionProvider; /** * Mandatory empty constructor for the fragment manager to instantiate the * fragment (e.g. upon screen orientation changes). */ public ItemDetailFragment() { } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //show ActionBar setHasOptionsMenu(true); //get data from DetailActivity fFeed = (RSSFeed) getArguments().getSerializable("feed"); fPos = getArguments().getInt("pos"); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { //inflate the fragment with the custom detail fragment View view = inflater .inflate(R.layout.detail_fragment, container, false); return view; } @SuppressLint("SetJavaScriptEnabled") @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); // Initialize views after the activity is created TextView title = (TextView) getView().findViewById(R.id.title); TextView author = (TextView) getView().findViewById(R.id.author); TextView date = (TextView) getView().findViewById(R.id.date); WebView wv = (WebView) getView().findViewById(R.id.desc); // Enable the vertical fading edge (by default it is disabled) ScrollView sv = (ScrollView) getView().findViewById(R.id.sv); sv.setVerticalFadingEdgeEnabled(true); // Set webview properties WebSettings ws = wv.getSettings(); //to show only one column, so that picture is always scaled correctly ws.setLayoutAlgorithm(LayoutAlgorithm.SINGLE_COLUMN); ws.setJavaScriptEnabled(true); Log.d("debug","In ItemDetailFragment mit Position: "+fPos+"und Feed: "+fFeed); //put in data title.setText(fFeed.getItem(fPos).getTitle()); author.setText(fFeed.getItem(fPos).getAuthor()); date.setText(fFeed.getItem(fPos).getDate()); wv.loadDataWithBaseURL("http://www.androidcentral.com/", fFeed .getItem(fPos).getDescription(), "text/html", "UTF-8", null); } //show share button in actionbar @Override public void onCreateOptionsMenu(Menu optionsMenu, MenuInflater inflater) { inflater.inflate(R.menu.activity_desc, optionsMenu); //get data from DetailActivity fFeed = (RSSFeed) getArguments().getSerializable("feed"); fPos = getArguments().getInt("pos"); // Locate MenuItem with ShareActionProvider MenuItem shareItem = optionsMenu.findItem(R.id.share_option); // Fetch and store ShareActionProvider mShareActionProvider = (ShareActionProvider) shareItem .getActionProvider(); Intent shareIntent = new Intent(Intent.ACTION_SEND); shareIntent.setType("text/plain"); shareIntent.putExtra(Intent.EXTRA_SUBJECT, "RSS"); String shareBody = fFeed.getItem(fPos).getTitle() + " - " + fFeed.getItem(fPos).getLink(); shareIntent.putExtra(Intent.EXTRA_TEXT, shareBody); // Set the share intent mShareActionProvider.setShareIntent(shareIntent); } //OnClick auf ActionBar @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case android.R.id.home: android.app.FragmentManager man = getActivity().getFragmentManager(); man.popBackStackImmediate(); return true; } return super.onOptionsItemSelected(item); } } </code></pre> <p>LogCat output:</p> <pre><code>11-13 21:33:05.848: E/AndroidRuntime(26792): FATAL EXCEPTION: main 11-13 21:33:05.848: E/AndroidRuntime(26792): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.example.ItemListActivity}: java.lang.NullPointerException 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2115) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2153) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread.access$700(ActivityThread.java:137) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1246) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.os.Handler.dispatchMessage(Handler.java:99) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.os.Looper.loop(Looper.java:137) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread.main(ActivityThread.java:5031) 11-13 21:33:05.848: E/AndroidRuntime(26792): at java.lang.reflect.Method.invokeNative(Native Method) 11-13 21:33:05.848: E/AndroidRuntime(26792): at java.lang.reflect.Method.invoke(Method.java:511) 11-13 21:33:05.848: E/AndroidRuntime(26792): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792) 11-13 21:33:05.848: E/AndroidRuntime(26792): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555) 11-13 21:33:05.848: E/AndroidRuntime(26792): at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:115) 11-13 21:33:05.848: E/AndroidRuntime(26792): at dalvik.system.NativeStart.main(Native Method) 11-13 21:33:05.848: E/AndroidRuntime(26792): Caused by: java.lang.NullPointerException 11-13 21:33:05.848: E/AndroidRuntime(26792): at de.example.onActivityCreated(ItemListFragment.java:117) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1508) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1884) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:566) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1163) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.Activity.performStart(Activity.java:5068) 11-13 21:33:05.848: E/AndroidRuntime(26792): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2088) 11-13 21:33:05.848: E/AndroidRuntime(26792): ... 12 more </code></pre> <p>The error leads to this line in ItemListFragment: <code>feed = (RSSFeed) getActivity().getIntent().getExtras().get("feed");</code></p> <p>If i press the back button in my ItemDetailFragment everything works fine, just the up navigation causes the error. Please help me;-)</p>
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    1. COGood thing you've worked out the line where the exception is raised. Now add debug code to determine which one of the `get()`s returns null. My money is on `getExtras()`.
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    2. COOnCreate is not called when going back, just onStart, so it makes sense that it doesn't crash on that.
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    3. CO@323go I added the line `Bundle be = getActivity().getIntent().getExtras();` but this throws no error @popovitsj so I have to check in the fragment if I come back from another fragment and then do not run this code, or?
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      1. POAndroid: NullPointerException in my Fragment using BackStack
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