Ich weiß nicht warum mein Code nicht speichertcheckbox geprüfter Wert; wenn ich @ checcheckbox und nachdem ich auf eine andere Registerkarte geklickt und zur vorherigen Registerkarte zurückgekehrt bin,checkbox ist nicht ausgewählt ... Ich hoffe, dass Sie den Fehler in meinem Code finden!

IDE sagt zu mir:FATAL EXCEPTION: main java.lang.NullPointerException at line ".onCreateView(holder.chkBox.setChecked(true);"

Warum

ADAPTER CLASS:

public abstract class PlanetAdapter extends ArrayAdapter<Planet> implements CompoundButton.OnCheckedChangeListener{

    private List<Planet> planetList;
    private Context context;
    ArrayList<Birra> objects;

    public PlanetAdapter(List<Planet> planetList, Context context) {
        super(context, R.layout.single_listview_item, planetList);
        this.planetList = planetList;
        this.context = context;
    }    

    public class PlanetHolder {
        public TextView planetName;
        public TextView distView;
        public TextView valuta;
        public CheckBox chkBox;
        public EditText edit;
        public String quantità;        
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        View row = convertView;
        PlanetHolder holder = null;
        if (row == null) {
            LayoutInflater inflater = ((Activity) context).getLayoutInflater();
            row = inflater.inflate(R.layout.single_listview_item, parent, false);
            holder = new PlanetHolder();
            holder.planetName = (TextView) row.findViewById(R.id.name);
            holder.distView = (TextView) row.findViewById(R.id.dist);
            holder.valuta = (TextView) row.findViewById(R.id.valuta);
            holder.chkBox = (CheckBox) row.findViewById(R.id.chk_box);
            holder.edit = (EditText) row.findViewById(R.id.editText);
            holder.edit.setVisibility(View.GONE);
            holder.edit.setEnabled(false);
            row.setTag(holder);
        } else {
            holder = (PlanetHolder) row.getTag();
        }

        final Planet p = planetList.get(position);        
        final PlanetHolder finalHolder = holder;

        holder.chkBox.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (finalHolder.chkBox.isChecked()) {
                    finalHolder.edit.setVisibility(View.VISIBLE);
                    finalHolder.edit.setEnabled(true);
                    SharedPreferences preferences = getContext().getSharedPreferences("MaterialTabs", android.content.Context.MODE_PRIVATE);

                    SharedPreferences.Editor mEditor = preferences.edit();
                    mEditor.putBoolean("CheckBox_Value", finalHolder.chkBox.isChecked());

                    mEditor.commit();

                    finalHolder.edit.addTextChangedListener(new TextWatcher() {
                        @Override
                        public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                        }

                        @Override
                        public void onTextChanged(CharSequence s, int start, int before, int count) {
                        }

                        @Override
                        public void afterTextChanged(Editable s) {
                            p.setQuantità(finalHolder.edit.getText().toString().trim());
                            SharedPreferences preferences = getContext().getSharedPreferences("PROJECT_NAME", android.content.Context.MODE_PRIVATE);
                            SharedPreferences.Editor editor = preferences.edit();
                            editor.putString("KEY", finalHolder.edit.getText().toString().trim());

                            editor.commit();

                        }
                    });
                } else {
                    finalHolder.edit.setVisibility(View.GONE);
                    finalHolder.edit.setEnabled(false);
                    finalHolder.edit.setText(null);

                }

            }
        });
        holder.planetName.setText(p.getName());
        holder.distView.setText("" + p.getDistance());
        holder.valuta.setText("" + p.getValuta());
        holder.chkBox.setChecked(p.isSelected());
        holder.chkBox.setTag(p);
        holder.edit.setEnabled(false);

        return row;
    }

    ArrayList<Planet> getBox() {
        ArrayList<Planet> box = new ArrayList<Planet>();
        for (Planet p : planetList) {
            if (p.selected)
                box.add(p);
        }
        return box;
    }
}

FRAGMENT

ListView lv;
ArrayList<Planet> planetList;
PlanetAdapter plAdapter;
BirraAdapter biAdapter;
PlanetAdapter.PlanetHolder holder;

 public class MyListFragment extends Fragment implements
        android.widget.CompoundButton.OnCheckedChangeListener {

    ListView lv;
    ArrayList<Planet> planetList;
    PlanetAdapter plAdapter;
    BirraAdapter biAdapter;
    PlanetAdapter.PlanetHolder holder;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment    
        ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_list2, container, false);

        Button mButton = (Button) rootView.findViewById(R.id.button);
        mButton.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
            showResult(v);


            }
        });

        return rootView;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        lv = (ListView)getView().findViewById(R.id.listview);
        displayPlanetList();
    }


    private void displayPlanetList() {

        planetList = new ArrayList<Planet>();
        planetList.add(new Planet("Margherita", 6, "€"));
        planetList.add(new Planet("Diavola", 7,"€"));
        planetList.add(new Planet("Bufalina", 5,"€"));
        planetList.add(new Planet("Marinara", 5,"€"));
        planetList.add(new Planet("Viennese", 4, "€"));

        plAdapter = new PlanetAdapter(planetList, getContext()) {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

                int pos = lv.getPositionForView(buttonView);
                if (pos != ListView.INVALID_POSITION) {
                    Planet p = planetList.get(pos);
                    p.setSelected(isChecked);      
                }        
            }
        };
        lv.setAdapter(plAdapter);
    }
    @Override
    public void onPause() {

        //get the instance variables
        SharedPreferences preferences = getContext().getSharedPreferences("MaterialTabs", android.content.Context.MODE_PRIVATE);
        boolean mCheckBoxValue = preferences.getBoolean("CheckBox_Value", false);

        if (mCheckBoxValue) {
            holder.chkBox.setChecked(true);        
        } else {
            holder.chkBox.setChecked(false);            
        }
        super.onPause();   
    }

    public void showResult(View v) {
        String  result2 = "Selected Product are :";
        int totalAmount2=0;

        String a="";
        for (Birra b : biAdapter.getBox()){

            if (b.selected){

                result2 += "\n" + b.name+" "+b.distance+"€"+"q.tà :"+b.getQuantità();
                int quantitaInt= Integer.parseInt(b.getQuantità());
                totalAmount2+=b.distance * quantitaInt;
            }
        }

        Toast.makeText(getActivity(), result2 + "\n" + "Total Amount:=" + totalAmount2 + "€", Toast.LENGTH_LONG).show();                                        
    }                
}