получение данных из firebase и создание списка с помощью флажка

проблема решена, теперь полностью проверьте мой код

ListViewCheckboxesActivity.java

package com.example.listview1;

public class ListViewCheckboxesActivity extends Activity
{

MyCustomAdapter dataAdapter = null;
FirebaseDatabase database;
DatabaseReference ref;
States states ;
States _states ;
ArrayList<States> stateList;
List<String> keys;

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_list);

    database= FirebaseDatabase.getInstance();
    ref=database.getReference("Stops");




    ref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            stateList = new ArrayList<States>();
            keys=new ArrayList<>();

            System.out.println("@@@@");
            //states=new States();
            System.out.println("@@@@");
            for(DataSnapshot ds: dataSnapshot.getChildren())
            {
                System.out.println(states=ds.getValue(States.class));
                if(states.isSelected()==false) {
                    keys.add(ds.getKey());
                    _states = new States(states.getCode(), states.getName(), states.isSelected());
                    states.setKey(ds.getKey());
                    System.out.println(states.getKey()+"  "+states.getName() + states.getCode() + states.isSelected());
                    stateList.add(_states);
                    System.out.println(stateList);

                }
            }

            displayListView();

            checkButtonClick();


        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
    //Generate list View from ArrayList

    //Generate list View from ArrayList
  //  displayListView();



}

private void displayListView()
{


    //create an ArrayAdaptar from the String Array
    dataAdapter = new MyCustomAdapter(this,R.layout.state_info, stateList);
    ListView listView = (ListView) findViewById(R.id.listView1);
    // Assign adapter to ListView
    listView.setAdapter(dataAdapter);

    listView.setOnItemClickListener(new OnItemClickListener()
    {

        public void onItemClick(AdapterView<?> parent, View view, int position, long id)
        {
            // When clicked, show a toast with the TextView text
            States state = (States) parent.getItemAtPosition(position);
            Toast.makeText(getApplicationContext(),"Clicked on Row: " + state.getName(),
                    Toast.LENGTH_LONG).show();
        }
    });
}

   private class MyCustomAdapter extends ArrayAdapter<States>
   {

    private ArrayList<States> stateList;

    public MyCustomAdapter(Context context, int textViewResourceId,

                           ArrayList<States> stateList)
    {
        super(context, textViewResourceId, stateList);
        this.stateList = new ArrayList<States>();
        this.stateList.addAll(stateList);
    }

    private class ViewHolder
    {
        TextView code;
        CheckBox name;
    }

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

        ViewHolder holder = null;

        Log.v("ConvertView", String.valueOf(position));

        if (convertView == null)
        {

            LayoutInflater vi = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);

            convertView = vi.inflate(R.layout.state_info, null);

            holder = new ViewHolder();
            holder.code = (TextView) convertView.findViewById(R.id.code);
            holder.name = (CheckBox) convertView.findViewById(R.id.checkBox1);

            convertView.setTag(holder);

            holder.name.setOnClickListener( new View.OnClickListener()
            {
                public void onClick(View v)
                {
                    CheckBox cb = (CheckBox) v;
                    States _state = (States) cb.getTag();

                    Toast.makeText(getApplicationContext(), "Clicked on Checkbox: " + cb.getText() + " is " + cb.isChecked(),
                            Toast.LENGTH_LONG).show();

                    _state.setSelected(cb.isChecked());
                }
            });

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

        States state = stateList.get(position);

        holder.code.setText(" (" + state.getCode() + ")");
        holder.name.setText(state.getName());
        holder.name.setChecked(state.isSelected());

        holder.name.setTag(state);

        return convertView;
    }

   }

   private void checkButtonClick()
   {

    Button myButton = (Button) findViewById(R.id.findSelected);

    myButton.setOnClickListener(new OnClickListener()
    {

        @Override
        public void onClick(View v)
        {

int j = 0; StringBuffer responseText = new StringBuffer();

            final ArrayList<States> statList = dataAdapter.stateList;

            for(int i=0;i<statList.size();i++)
            {
                final States sta = statList.get(i);

                if(sta.isSelected()) {
                    responseText.append("\n" + sta.getName());
           j  = j +  sta.getCode();
                    System.out.println("@@@@@@@@@@@@");
                    System.out.println("@@@@@@@@@@@@@");
                    System.out.println("@@@@@@@@@@@@");
                    System.out.println("!!!!!!!!!!!!!");
           System.out.println(keys.get(i));

          // ref=database.getReference("stops").child("")

                }
            }
            if(j<=15) {
                 responseText.append("The following were selected \n");
                Toast.makeText(getApplicationContext(),
                        responseText+" Your total number of students "+ j, Toast.LENGTH_LONG).show();


                for(int i=0;i<statList.size();i++)
                {
                    final States sta = statList.get(i);

                    if(sta.isSelected()) {

                        database.getReference("Stops").child(keys.get(i)).child("selected").setValue(true);



                    }   // ref=database.getReference("stops").child("")

                }

                System.out.println("@@@@@@@@@@@@");
                System.out.println("@@@@@@@@@@@@@");
                System.out.println("@@@@@@@@@@@@");
                System.out.println("!!!!!!!!!!!!!");

            }
            else
            {
                responseText.append(" Does not comes under bus seats limited to 15\n");
                Toast.makeText(getApplication(),
                        responseText, Toast.LENGTH_LONG).show();
                for(int i=0;i<statList.size();i++)
                {
                    final States stat = statList.get(i);

                   stat.setSelected(false);



                }
                displayListView();

            }
        }
    });
   }

   }

States.java

 package com.example.listview1;

 public class States
 {

int code ;
String name ;
boolean selected ;
String key;

public String getKey() {
    return key;
}

public void setKey(String key) {
    this.key = key;
}

public States() {
}

public States(int code, String name, boolean selected) {
    this.code = code;
    this.name = name;
    this.selected = selected;
}

public int getCode() {

    return code;
}

public void setCode(int code) {
    this.code = code;
}

public String getName() {
    return name;
}

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

public boolean isSelected() {
    return selected;
}

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

}

Иерархия базы данных "Остановки": {"01": {"code": 3, "name": "PALASIA", "selected": true}, "02": {"code": 6, "name": "mr10 "," selected ": true}," 03 ": {" code ": 2," name ":" NAVLAKHA "," selected ": true}," 04 ": {" code ": 4," name ": "BHAWARKUA", "selected": false}, "05": {"code": 2, "name": "MEGHDOOT GARDEN", "selected": false}, "06": {"code": 4, " name ":" VISHNUPURI COLONY "," selected ": false}," 07 ": {" code ": 6," name ":" VIJAY NAGAR "," selected ": false}," 08 ": {" code ": 9, "name": "MR 9", "selected": false}, "09": {"code": 4, "name": "BAPAT CHAURAHA", "selected": false}},

Предположим, у вас структура firebase такая.

States
    autoId(XQSKNDLALALALDX...)
        code
        name
        selected
    autoId(XQSKNDLALALALDX...)
        code
        name
        selected

ваш пожарный запрос

MyCustomAdapter mAdapter = new MyCustomAdapter(this);

DatabaseReference dbRef = mDatabase.child("States");
dbRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            if (dataSnapshot.exists()) {
                State state = dataSnapshot.getValue(State.class);
                mAdapter.addState(state);
            }
        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) { }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) { }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) { }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) { }
    });

Ваш адаптер

 public class MyCustomAdapter extends RecyclerView.Adapter {

private List<State> stateList = new ArrayList<State>();
private Context mContext;
private LayoutInflater mInflater;

public MyCustomAdapter(Context context) {
    this.mContext = context;
    this.mInflater = LayoutInflater.from(mContext);
}

public void addState(State state) {
    this.stateList.add(state);
    this.notifyItemInserted(mChatList.size() - 1);
}

@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {

      //...
}

@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int position) {

     //...
    }
}

Можете ли вы изменить конструктор адаптера

MyCustomAdapter( ChildEventListener childEventListener, int textViewResourceId, ArrayList<States> stateList)

в

MyCustomAdapter( ListViewCheckboxesActivity activity, int textViewResourceId, ArrayList<States> stateList)

при инициализации в действии отправьте ListViewCheckboxesActivity.this в качестве значения и попробуйте один раз

Ваш конструктор пытается привести ChildEventListener к контексту, который вызывает исключение