Darin Beaudreau Darin Beaudreau - 25 days ago 16
Java Question

Bundle being passed to Fragment is null?

I'm working on a tab layout with several fragments which need to have an object passed to them from a previous activity so they can populate their lists, and I'm running into an error when I try to retrieve that object from the bundle. I have previously passed this same object between other activities with no issue. I made the object Parcelable so I can add it to a bundle and pass it as an argument. Here is the code for the adapter class that spits out the Fragments used in the tab layout:

package edu.uml.android.adventurersarchive;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;

import edu.uml.android.adventurersarchive.character.CharacterInfo;

public class SpellbookTabAdapter extends FragmentPagerAdapter {
private Context mContext;
private CharacterInfo myCharacter;

public SpellbookTabAdapter(Context context, CharacterInfo ch, FragmentManager fm) {
super(fm);
mContext = context;
myCharacter = ch;
}

@Override
public Fragment getItem(int position) {
Bundle bundle = new Bundle();
if(position == 0) {
PreparedSpellsFragment prepared = new PreparedSpellsFragment();
bundle.putParcelable("character", myCharacter);
prepared.setArguments(bundle);
return prepared;
} else if(position == 1) {
MySpellbookFragment myspellbook = new MySpellbookFragment();
bundle.putParcelable("character", myCharacter);
myspellbook.setArguments(bundle);
return myspellbook;
} else if(position == 2) return new FullSpellbookFragment();
else return null;
}

@Override
public int getCount() {
return 3;
}

@Override
public CharSequence getPageTitle(int position) {
if(position == 0) return "Prepared";
else if(position == 1) return "My Spells";
else if(position == 2) return "All Spells";
else return "";
}
}


Here is the PreparedSpellsFragment class. The code is almost identical in the MySpellbookFragment class (with the exception of how the fragment interacts with the object):

package edu.uml.android.adventurersarchive;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ExpandableListView;
import android.widget.ExpandableListView.OnChildClickListener;

import java.util.List;
import java.util.Map;

import edu.uml.android.adventurersarchive.character.CharacterInfo;
import edu.uml.android.adventurersarchive.info.Spell;

public class PreparedSpellsFragment extends Fragment {
private SpellListAdapter adapter;
private List<String> groupHeaders;
private Map<String, List<Spell>> groupItems;

public PreparedSpellsFragment() {
Bundle bundle = getArguments();
CharacterInfo myCharacter = (CharacterInfo) bundle.getParcelable("character");
prepareGroups(myCharacter);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.spell_list, container, false);

adapter = new SpellListAdapter(groupHeaders, groupItems);
ExpandableListView expView = (ExpandableListView) rootView.findViewById(R.id.spell_list);
expView.setAdapter(adapter);

expView.setOnChildClickListener(new OnChildClickListener() {
@Override
public boolean onChildClick(ExpandableListView parent, View v, int groupPosition, int childPosition, long id) {
// TODO: Launch activity to show detailed information about the spell.
return false;
}
});

return rootView;
}

private void prepareGroups(CharacterInfo myCharacter) {
// TODO: Take spells in player's prepared list and populate the groups and their items.
if(myCharacter != null) {

}
}
}


I get an error saying that in the PreparedSpellsFragment constructor, I'm invoking the "getParcelable()" method on a null object reference, suggesting the Bundle object retrieved from "getArguments()" is null, but I can't see any reason for the bundle itself to be null, short of maybe an OutOfMemoryException, where it could not allocate space for the object. I could understand if maybe the object just hadn't been passed correctly or if there was a typo in the string for the key representing the object, but no... it says the Bundle object itself is null.

Can anyone figure out what the cause is?

Answer

You are checking the Bundle in the constructor. Get rid of the constructors and check the Bundle in onCreateView() of the fragment instead.

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