It is very difficult for me to try to understand this. I get a NullPointerException when switching between Fragments with a RecyclerView , but only in a specific order. Code and exception below. First explanation:
I have a snippet with this tab as shown here: 
3 of these tabs use the same fragment containing RecyclerView: Schedule, History and Test. Any of them will work if I select them first. Now the problem is that I go to one of the other aforementioned tabs to the right of the first one I selected! If I go to the left of the first one I selected, it will be very easy to boot.
If I select "Test", go to "History" and then "Schedule" will work fine
If I select Test, then Schedule these two will work, but then go to History, an exception.
If you select Schedule and History, an exception will occur.
If I choose History, then the Schedule of the two will work, but then go to Testing.
If I choose History, then Test will happen.
I extended the RecycleView and put the gap in onMeasure to see if I could figure out what was happening, and I noticed that the mAdapter RecyclerView was null . I checked inside setAdapter() RecyclerView and it was always passed by a valid adapter. It seems that at some point the mAdapter is cleared. I just can't understand why this happens when I open tabs going from left to right, and not from right to left ...
Any help would be appreciated as I reached this goal!
Here is the NullPointerException:
Link to exception tracing (If this were done to avoid character restrictions)
EDIT: After you select NullPointerException and IllegalStateException . Looks from LayoutManager . Here is a link to this conclusion
Here is a snippet for tabbed browsing:
public class FKitViewer extends Fragment implements OnTabChangeListener { public static final String TAB_INFO = "Info"; public static final String TAB_SCHEDULE = "Schedule"; public static final String TAB_HISTORY = "History"; public static final String TAB_TEST = "Test"; public static final String TAB_REQS = "Reqs"; private View mRoot; private TabHost mTabHost; private int mCurrentTab; @Override public void onAttach(Activity activity){ super.onAttach(activity); } @Override public View onCreateView(LayoutInflater li, ViewGroup container, Bundle savedInstanceState){ mRoot = li.inflate(R.layout.kit_view, container); mTabHost = (TabHost) mRoot.findViewById(android.R.id.tabhost); setupTabs(); return mRoot; } @Override public void onActivityCreated(Bundle savedInstanceState){ super.onActivityCreated(savedInstanceState); setRetainInstance(true); mTabHost.setOnTabChangedListener(this); mTabHost.setCurrentTab(mCurrentTab); updateTab(TAB_INFO, R.id.tab1); } private void setupTabs(){ mTabHost.setup(); mTabHost.addTab(newTab(TAB_INFO, "Info", R.id.tab1)); mTabHost.addTab(newTab(TAB_SCHEDULE, "Schedule", R.id.tab2)); mTabHost.addTab(newTab(TAB_HISTORY, "History", R.id.tab3)); mTabHost.addTab(newTab(TAB_REQS, "Reqs", R.id.tab4)); mTabHost.addTab(newTab(TAB_TEST, "Test", R.id.tab5)); } private TabSpec newTab(String tag, String label, int tabContentId){ TabSpec tabSpec = mTabHost.newTabSpec(tag); tabSpec.setIndicator(label); tabSpec.setContent(tabContentId); return tabSpec; } private void updateTab(String tabId, int placeholder){ FragmentManager fm = getFragmentManager(); if(fm.findFragmentByTag(tabId) == null){ if(tabId.equals(TAB_INFO)) fm.beginTransaction() .replace(placeholder, new FListiesView(), tabId) .commit(); if(tabId.equals(TAB_SCHEDULE)) fm.beginTransaction() .replace(placeholder, new FKitSchedule(false), tabId) .commit(); if(tabId.equals(TAB_HISTORY)) fm.beginTransaction() .replace(placeholder, new FKitSchedule(true), tabId) .commit(); if(tabId.equals(TAB_REQS)) fm.beginTransaction() .replace(placeholder, new KitRequirements(), tabId) .commit(); if(tabId.equals(TAB_TEST)) fm.beginTransaction() .replace(placeholder, new FKitSchedule(false), tabId) .commit(); } } @Override public void onTabChanged(String tabId){ Log.d("MNB", "Changing to tab: " + tabId); if(TAB_INFO.equals(tabId)){ updateTab(tabId, R.id.tab1); mCurrentTab = 0; return; } if(TAB_SCHEDULE.equals(tabId)){ getActivity().getIntent().getExtras().putBoolean("com.crummy.history", false); updateTab(tabId, R.id.tab2); mCurrentTab = 1; return; } if(TAB_HISTORY.equals(tabId)){ getActivity().getIntent().getExtras().putBoolean("com.crummy.history", true); updateTab(tabId, R.id.tab3); mCurrentTab = 2; return; } if(TAB_REQS.equals(tabId)){ updateTab(tabId, R.id.tab4); mCurrentTab = 3; return; } if(TAB_TEST.equals(tabId)){ getActivity().getIntent().getExtras().putBoolean("com.crummy.history", true); updateTab(tabId, R.id.tab5); mCurrentTab = 4; return; } } }
Here is a snippet:
public class RVFKitSchedule extends Fragment
implements LoaderManager.LoaderCallbacks {
private String mGetURL = "/index.php/droid/kitreport/"; private String mHistoryURL = "/index.php/droid/kithistory/"; private String mUpdateStatusURL = "/index.php/order_status/update/"; private Boolean mIsHistory = false; private LinearLayout mPbl; private int mDialogStatusLevel = 0; private int mDialogLineId = -1; private List<ScheduleRowModel> mItems = null; private FKVRecyclerView mRecyclerView; private KitScheduleRVAdapter mRVAdapter; private int mItemCount; private RecyclerView.LayoutManager mLayoutManager; private FragmentActivity mParentActivity; public RVFKitSchedule(){ } public RVFKitSchedule(boolean isHistory){ mIsHistory = isHistory; if(mIsHistory) mGetURL = mHistoryURL; } @Override public View onCreateView(LayoutInflater li, ViewGroup vg, Bundle b){ super.onCreateView(li, vg, b); return li.inflate(R.layout.rv_main, vg, false); } @Override public void onActivityCreated(Bundle icicle){ super.onActivityCreated(icicle); final InputMethodManager imm = (InputMethodManager) mParentActivity.getSystemService(Context.INPUT_METHOD_SERVICE); imm.hideSoftInputFromWindow(getView().getWindowToken(), 0); } @Override public void onViewCreated(View view, Bundle icicle){ super.onViewCreated(view, icicle); mParentActivity = getActivity(); mRecyclerView = (FKVRecyclerView)mParentActivity.findViewById(R.id.recyclerView); mLayoutManager = new LinearLayoutManager(mParentActivity); //mLayoutManager.setOrientation(LinearLayoutManager.VERTICAL); //mLayoutManager. mLayoutManager.scrollToPosition(0); mRecyclerView.setLayoutManager(mLayoutManager); RecyclerView.ItemDecoration itemDecoration = new DividerItemDecoration(mParentActivity, DividerItemDecoration.VERTICAL_LIST); mRecyclerView.addItemDecoration(itemDecoration); mItems = new ArrayList<ScheduleRowModel>(); mRVAdapter = new KitScheduleRVAdapter(mItems, mIsHistory); //mRecyclerView.setAdapter(null); if(mRecyclerView.getAdapter() != null) mRecyclerView.swapAdapter(mRVAdapter, true); else mRecyclerView.setAdapter(mRVAdapter); mRecyclerView.addOnItemTouchListener( new RecyclerItemClickListener(mParentActivity, new RecyclerItemClickListener.OnItemClickListener(){ @Override public void onItemClick(View v, int position){ String status = ((TextView)v.findViewById(R.id.sr_status)).getText().toString(); if(status.equals("Open")) mDialogStatusLevel = 0; else if(status.equals("In Production")) mDialogStatusLevel = 1; else if(status.equals("Waiting")) mDialogStatusLevel = 2; else if(status.equals("Ready")) mDialogStatusLevel = 3; else if(status.equals("Shipped")) mDialogStatusLevel = 4; int lineId = Integer.parseInt(((TextView)v.findViewById(R.id.sr_order_line_id)).getText().toString()); mDialogLineId = lineId; OrderStatusDialog df = new OrderStatusDialog(mParentActivity, mDialogStatusLevel){ @Override protected void onDialogClick(DialogInterface di, final int which){ Runnable update = new Runnable(){ @Override public void run(){ updateStatus(mDialogLineId, which); } }; Thread t = new Thread(null, update, "MagentoBackground"); t.start(); try{ t.join(); }catch(InterruptedException e){ e.printStackTrace(); } restartLoading(); dismiss(); } }; df.show(getFragmentManager(), "dialog"); } }){ @Override public void onItemLongClick(View v, int pos){ String s = ((TextView)v.findViewById(R.id.sr_pn)).getText().toString(); String n = ((TextView)v.findViewById(R.id.sr_pn)).getText().toString(); CheckItemTypeTask task = new CheckItemTypeTask(s, null); task.execute(mParentActivity); int type = -1; try{ type = task.get(); }catch(Exception e){ e.printStackTrace(); } if(type == ItemType.PART){ openPartViewer(s); }else if(type == ItemType.KIT){ openKitViewer(s,n); }else if(type == ItemType.ERROR){ Toast.makeText(mParentActivity, "Error getting item type!", Toast.LENGTH_LONG); }else{ Toast.makeText(mParentActivity, "Invalid item type!", Toast.LENGTH_LONG).show(); } } } ); if(mParentActivity.getIntent().getExtras() != null){ Bundle b = mParentActivity.getIntent().getExtras(); if(!b.isEmpty()){ mGetURL += b.getString("com.crummy.kitNum"); } } mPbl = (LinearLayout)mParentActivity.findViewById(R.id.main_pbl); mPbl.setVisibility(View.VISIBLE); LoaderManager lm = getLoaderManager(); if(lm.getLoader(0) != null){ lm.initLoader(0, null, this); } startLoading(); } protected void startLoading(){ getLoaderManager().initLoader(0, null, this); } protected void restartLoading(){ getLoaderManager().restartLoader(0, null, this); } @Override public Loader<Void> onCreateLoader(int arg0, Bundle arg1){ Log.d("MNB", "FKitSchedule: onCreateLoader"); AsyncTaskLoader<Void> loader = new AsyncTaskLoader<Void>(mParentActivity){ @Override public Void loadInBackground(){ try{ getLines(); }catch(Exception e){ e.printStackTrace(); } return null; } }; loader.forceLoad(); return loader; } @Override public void onLoadFinished(Loader<Void> arg0, Void arg1){ Log.d("MNB", "FKitSchedule: onLoadFinished"); mPbl.setVisibility(View.GONE); } @Override public void onLoaderReset(Loader<Void> arg0){ } protected boolean openKitViewer(String kitNum, String kitName){ boolean result = false; Intent i = new Intent(mParentActivity, GenFragmentActivity.class); i.putExtra("com.crummy.frag_layout_id", R.layout.kit_view_frag); i.putExtra("com.crummy.kitNum", kitNum); i.putExtra("com.crummy.kitName", kitName); startActivity(i); return result; } protected boolean openPartViewer(String itemNum){ boolean result = false; Intent i = new Intent(mParentActivity, PartInfoFragmentActivity.class); i.putExtra("com.crummy.partnum", itemNum); startActivity(i); return result; } protected void getLines(){ Log.d("MNB", "FKitSchedule: getLines() "); try{ HttpEntity response = HttpHelper.tryHttp(mParentActivity, mGetURL, null); if(response == null) return; String res = EntityUtils.toString(response); if(res.equals("[]")){ mParentActivity.runOnUiThread(noKitsError); return; } JSONArray jsona = new JSONArray(res); mItems = new ArrayList<ScheduleRowModel>(); Log.d("MNB", "jsona.length() = " + jsona.length()); for(int i=0; i < jsona.length(); i++){ Log.d("MNB", "Reading json line " + i); JSONObject j = (JSONObject) jsona.get(i); ScheduleRowModel srm = new ScheduleRowModel(); srm.custPo = j.getString("custPo"); srm.dueDate = j.getString("dueDate"); srm.partNum = j.getString("KitNumber"); srm.qty = j.getInt("quantity"); srm.status = j.getString("status"); srm.lineId = j.getInt("id"); srm.company = j.getString("name"); srm.rev = j.getString("rev"); if(!mIsHistory){ if(!j.getString("note").equals("null")) srm.note = j.getString("note"); } mItems.add(srm); } }catch(Exception e){ e.printStackTrace(); } mParentActivity.runOnUiThread(returnRes); } private void addItemToList(ScheduleRowModel model){ mItemCount++; mRVAdapter.addData(model); } private HttpEntity updateStatus(int lineId, int statusId){ HttpEntity resEntityPost = null; try{ HttpClient client = new DefaultHttpClient(); String host = HttpHelper.getHost(mParentActivity); HttpPost post = new HttpPost(host + mUpdateStatusURL); List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2); nameValuePairs.add(new BasicNameValuePair("line_id", Integer.toString(lineId))); nameValuePairs.add(new BasicNameValuePair("status", Integer.toString(statusId))); post.setEntity(new UrlEncodedFormEntity(nameValuePairs)); HttpResponse res = client.execute(post); resEntityPost = res.getEntity(); }catch(Exception e){ e.printStackTrace(); } return resEntityPost; } protected Runnable returnRes = new Runnable(){ @Override public void run(){ Log.d("MNB", "FKitSchedule returnRes "); mItemCount = 0; mRVAdapter.clear(); if(mItems != null && mItems.size() > 0){ for(int i = 0; i < mItems.size(); i++){ addItemToList(mItems.get(i)); } } } }; private Runnable noKitsError = new Runnable() { public void run(){ Toast t = Toast.makeText(mParentActivity, "No orders for this kit.", Toast.LENGTH_SHORT); t.show(); } };
}
Here is the RecyclerView.Adapter:
import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; import java.util.List; import java.util.Locale; import android.support.v7.widget.RecyclerView; import android.util.Log; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; public class KitScheduleRVAdapter extends RecyclerView.Adapter<KitScheduleRVAdapter.ScheduleRowViewHolder>{ private List<ScheduleRowModel> items; private boolean mIsHistory = false; KitScheduleRVAdapter(List<ScheduleRowModel> modelData, boolean isHistory){ Log.d("MNB", "Constructing KitScheduleRVAdapter"); if(modelData == null){ throw new IllegalArgumentException( "modelData must not be null"); } this.items = modelData; mIsHistory = isHistory; } @Override public ScheduleRowViewHolder onCreateViewHolder(ViewGroup vg, int viewType){ Log.d("MNB", "KitScheduleRVAdapter.onCreateViewHolder()"); View itemView = LayoutInflater .from(vg.getContext()) .inflate(R.layout.schedule_row, vg, false); return new ScheduleRowViewHolder(itemView); } @Override public void onBindViewHolder(ScheduleRowViewHolder vh, int pos){ Log.d("MNB", "Binding Viewholder at pos "+pos); ScheduleRowModel model = items.get(pos); vh.date.setText(model.dueDate); vh.po.setText(model.custPo); vh.partnum.setText(model.partNum); vh.qty.setText(""+model.qty); vh.status.setText(model.status); vh.id.setText(""+model.lineId); vh.company.setText(model.company); vh.rev.setText(model.rev); vh.note.setText(model.note); Calendar cutoff = Calendar.getInstance(); cutoff.add(Calendar.DAY_OF_MONTH, 14); Date co = cutoff.getTime(); SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd", Locale.US); Date d = new Date(); try { d = s.parse(model.dueDate); } catch (ParseException e) {