Custom List view (checkbox issue) ...setOnCheckedChangeListener

Question

I have a custom Listview each row in it consist of textview and checkbox. (1)when I click on item in list it should go to other activity and(2) when the checkbox is checked, the value in textview should be added to array//when it is unchecked the value should be removed from the array. the first requirement run successfuly with me, but the second one doesn't work. this is my code:

public class DataAdapter extends ArrayAdapter<ItemInList> {


public ArrayList<ItemInList> list;

public Activity context;
public LayoutInflater inflater;
public static ArrayList<String> array=new ArrayList<String>();
ItemInList element=new ItemInList();

public DataAdapter(Activity context,int x,ArrayList<ItemInList> list) {
    super(context, 0, list);
    this.context = context;
    this.list = list;
    this.inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}


static class ViewHolder {
    protected TextView name,Description;
    protected CheckBox checkbox;
}

public int getCount() {
    // TODO Auto-generated method stub
    return list.size();
}

@Override
public ItemInList getItem(int position) {
    // TODO Auto-generated method stub
    return list.get(position);
}

@Override
public long getItemId(int position) {
    // TODO Auto-generated method stub
    return 0;
}

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

   final ViewHolder holder;



    if (convertView == null) {

         holder = new ViewHolder();
            convertView = inflater.inflate(R.layout.row1, null);


        holder.name = (TextView) convertView.findViewById(R.id.food_title);
        holder.name.setTextColor(Color.BLACK);

        holder.Description = (TextView) convertView.findViewById(R.id.food_description);
        holder.Description.setTextColor(Color.GRAY);

        holder.checkbox = (CheckBox) convertView.findViewById(R.id.add_food_item);


        holder.checkbox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                    @Override
                    public void onCheckedChanged(CompoundButton buttonView,
                        boolean isChecked) {
                        element = (ItemInList) holder.checkbox.getTag();
                        element.setSelected(buttonView.isChecked());
                            if(element.isSelected())
                            {
                                array.add(element.getName());
                            }
                            else
                            {
                                array.remove(position);
                            }
                                            }
                });
         convertView.setTag(holder);


    } else {
         holder=(ViewHolder)convertView.getTag();

            ItemInList bean = (ItemInList) list.get(position);

            holder.name.setText( bean.getName());
            holder.Description.setText( bean.getDescription()+"");
            holder.checkbox.setChecked( bean.isSelected());

              return convertView;
    }



    holder.name.setText(list.get(position).getName());
    holder.Description.setText(list.get(position).getDescription()+"");
    holder.checkbox.setChecked(list.get(position).isSelected());

      return convertView;
}

the errors:

 null pointer exception..
                                at  DataAdapter$1.onCheckedChanged(DataAdapter.java:92)
    E/AndroidRuntime(543):  at android.widget.CompoundButton.setChecked(CompoundButton.java:125)
    E/AndroidRuntime(543):  at sehaty.com.DataAdapter$1.onCheckedChanged(DataAdapter.java:92)
   E/AndroidRuntime(543):   at android.widget.CompoundButton.setChecked(CompoundButton.java:125)
                                at android.widget.CompoundButton.performClick(CompoundButton.java:99)

any help will be appreciated

Answer 1

As I already stated in comments: you try to get the tag from your checkbox but you never set the tag. So element must be null. Thus you get a NullPointer. The question is..why do you try to get the tag? There is no need using that method (if i understand your intention correctly). You want to access your element variable for the corresponding postion. That element is in your list so you can try the following (the code is not tested..just copied from you and made some changes):

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

final ViewHolder holder;

   if (convertView == null) {
        holder = new ViewHolder();
        convertView = inflater.inflate(R.layout.row1, null);
        holder.name = (TextView) convertView.findViewById(R.id.food_title);
        holder.name.setTextColor(Color.BLACK);
        holder.checkbox = (CheckBox) convertView
                .findViewById(R.id.add_food_item);
        convertView.setTag(holder);

    } else {
        holder = (ViewHolder) convertView.getTag();
    }

    final ItemInList element = list.get(position);
    holder.name.setText(element.getName());
    holder.checkbox.setChecked(element.isSelected());
    holder.checkbox
            .setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(CompoundButton buttonView,
                        boolean isChecked) {
                    element.setSelected(buttonView.isChecked());

                    if (element.isSelected()) {
                        array.add(element.getName());
                    } else {
                        if (position < array.size())
                            array.remove(position);
                    }
                }
            });

    return convertView;
}

Answer 2

In the following line

element = (ItemInList) holder.checkbox.getTag();

you are trying to get a Tag from the checkbox, which is not beng set anywhere in the getView(). As a result it returns null.

Answer 3

Check line 92 in your DataAdapter class. It looks like the adapter (or other var?) is null. Have you instantiated all objects? If this doesn't help, please post your full code including XML.