hy everybody, i don't know why my code not save checkbox checked value; if i check checkbox and after i click on another tab and comeback to previous tab, checkbox is not selected...i hope that you find the error in my code!

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

why?

thanks in advance!

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;
      if(p.isCheckBoxchecked ())
      {
          finalHolder.chkBox.setChecked(true);
      }
      /*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);
      }*/

      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 editor = preferences.edit();
                  editor.putBoolean("showActivity", finalHolder.chkBox.isChecked());
                  editor.commit();*/
                 // boolean value= true;
                  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:

```
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);
    SharedPreferences preferences = getContext().getSharedPreferences("MaterialTabs", android.content.Context.MODE_PRIVATE);
      // preferences.getBoolean("showActivity", false);
       //preferences.getString("KEY", null);
    boolean mCheckBoxValue = preferences .getBoolean("CheckBox_Value", false);
    if (mCheckBoxValue) {
        holder.chkBox.setChecked(true);
    } else {
        holder.chkBox.setChecked(false);
    }

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

        }
    });
    //return inflater.inflate(R.layout.fragment_list2, container, false);
    return rootView;
}

```

PLANET:

```
class Planet {

    String name;
    int distance;
    String quantità;
    String valuta;
    boolean selected = false;
    boolean mCheckBoxState;

    public Planet(String name, int distance, String valuta) {
        super();
        this.name = name;
        this.distance = distance;
        this.valuta = valuta;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getDistance() {
        return distance;
    }

    public void setDistance(int distance) {
        this.distance = distance;
    }

    public boolean isSelected() {
        return selected;
    }

    public void setSelected(boolean selected) {
        this.selected = selected;
    }

    public String getQuantità() {
        return quantità;
    }

    public void setQuantità(String quantità) {
        this.quantità = quantità;
    }
    public String getValuta() {
        return valuta;
    }

    public void setValuta(String valuta) {
        this.valuta = valuta;
    }

    public boolean isCheckBoxchecked () { return mCheckBoxState; }
    private void setCheckBoxCheck(boolean state){ mCheckBoxState = state; }

}

```