Android checkbox selection in listivew

In my android application I am storing all the details of contact list in mobile to a listview and a checkbox is added to it for selecting a particular contact.. but there is some problem in selecting checkbox, app is crashing while selecting I am giving the code below.. if anyone can help please help

 btnSend.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                int count = listView.getCount();



                for(int i=0;i<count;i++) {
                    ViewGroup item = (ViewGroup) listView.getChildAt(i);
                    checkBox = ((CheckBox) item.findViewById(R.id.selected));

                    if(checkBox.isChecked()) {

                        Toast.makeText(SendMessagesActivity.this, "How are u", Toast.LENGTH_LONG)
                                .show();
                    }
                }


            }
        });

ContactsAdapter

public class ContactsAdapter extends BaseAdapter
{
    private Context context;
    private ArrayList<Contact> contacts;
    SparseBooleanArray sba=new SparseBooleanArray();

    public ContactsAdapter(Context context, ArrayList<Contact> contacts)
    {
        this.context = context;
        this.contacts = contacts;

    }




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

        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View gridView;
        final ViewHolder mHolder;

        if (convertView == null)
        {


            // gridView = new View(context);
            // get layout from mobile.xml
            //gridView = inflater.inflate(R.layout.contact, null);
            convertView = inflater.inflate(R.layout.contact, null);
            mHolder = new ViewHolder();

            mHolder.textName     =(TextView) convertView.findViewById(R.id.name);
            mHolder.textMobile   =(TextView) convertView.findViewById(R.id.mobile);
            mHolder.textSelector =(CheckBox) convertView.findViewById(R.id.selected);



            convertView.setTag(mHolder);



               /* TextView textName = (TextView) gridView.findViewById(R.id.name);
                textName.setSelected(true);
                textName.setText(contacts.get(position).getName());*/
               // cname = String.valueOf(contacts.get(position).getName());


               /* TextView textMobile = (TextView) gridView.findViewById(R.id.mobile);
                textMobile.setText(contacts.get(position).getMobile());*/
               // cmob = String.valueOf(contacts.get(position).getMobile());
            }



        else
        {
            //gridView = convertView;

            mHolder = (ViewHolder) convertView.getTag();

        }

        mHolder.textMobile.setText(contacts.get(position).getMobile());
        mHolder.textName.setText(contacts.get(position).getName());
        mHolder.textName.setSelected(true);
        mHolder.textSelector.setChecked(sba.get(position));

        mHolder.textSelector.setOnClickListener(new View.OnClickListener()
        {
            @Override
            public void onClick(View v) {

                 if(mHolder.textSelector.isChecked())
                 {
                     sba.put(position, true);
                 }

                else
                {
                    sba.put(position, false);
                }

            }
        });


        // return gridView;

        return convertView;
    }




    private class ViewHolder
    {
        private TextView textMobile,textName;
        private CheckBox textSelector;
    }

    @Override
    public int getCount()
    {
        return contacts.size();
    }

    @Override
    public Object getItem(int position)
    {
        return null;
    }

    @Override
    public long getItemId(int position)
    {
        return 0;
    }

}