Why notifyItemChanged(int position) of RecyclerView is working only once than thrice?

Question

I am trying to replicate the action of Recyclerview methods wherein I am having 3 items in ArrayList itemname and also stored in sqlite table. Corresponding to each item name an 'id' is assigned in the table. Here I want that for each below iteration all the 3 items shall change color as per the condition defined in the onBindViewHolder() method of the Adapter class.

for (int i=0; i<itemname.size(); i++) {   
String query = "SELECT id FROM sec_table WHERE address='"+itemname.get(i)+"'";
                 Cursor c1 = SecDB.rawQuery(query,null);

                 if (c1 != null && c1.getCount() != 0)
                 {
                     while (c1.moveToNext()) {
                         id = c1.getInt(c1.getColumnIndex("id"));
                     }
                        c1.close();
                 }

      alert_position = id;                // Class variable 'alert_position'
      userAdapter.notifyItemChanged(alert_position);
}

The onBindViewHolder() method is responsible for changing the color of the cards as per the value of the position variable in the Main class.

@Override                // Inside the Adapter class
public void onBindViewHolder(@NonNull final UserViewHolder holder, final int position) {
    final SecurityDetails userDetails = secDetailsList.get(position);
    LogsDatabaseHelper logsDBHelper = new LogsDatabaseHelper(context);


    SecurityDatabaseHelper secDBHelper = new SecurityDatabaseHelper(context);
    LogsDB = logsDBHelper.getWritableDatabase();
    SecDB = secDBHelper.getWritableDatabase();

    if (requestQueue==null)
    requestQueue = Volley.newRequestQueue(context);      // Creating RequestQueue...

    holder.tvName.setText(userDetails.getName());

    if(position == Security.alert_position) {
        Toast.makeText(context, position+"", Toast.LENGTH_SHORT).show();
        holder.state.setText("< Activity Detected >");
        holder.state.setTextColor(Color.RED);
        holder.cards.setBackgroundColor(0x33FF0000);
    }
  }

Here the above for loop is changing the color of the last card only although it is feeding position values 1,2,3 simultaneously to the notifyItemChanged().

---

But when the same logic of updating the cards is performed via android Volley all 3 cards are turning red one by one. The volley method is shown below:

for (int i=0; i<itemname.size(); i++) {   // Calls the Volley method with different items name from arraylist
      CardsUpdate(itemname.get(i));
}

private void CardsUpdate(final String email) {
    StringRequest stringRequest = new StringRequest(Request.Method.POST, "http://plateau.com/SecuritySensorUpdate.php", new Response.Listener<String>()
    {
        int id;
        @Override
         public void onResponse(String ServerResponse) {
            if (ServerResponse.equalsIgnoreCase("1")) {
                ContentValues values = new ContentValues();
                values.put(SecurityDatabaseContract.UserDatabase2.SEC_NAME_COL4, "1");
                SecDB.update(SecurityDatabaseContract.UserDatabase2.TABLE_NAME2, values, "address='" + email + "'", null);

                String query = "SELECT id FROM sec_table WHERE address='" + email + "'";
                Cursor c1 = SecDB.rawQuery(query, null);

                if (c1 != null && c1.getCount() != 0) {
                    while (c1.moveToNext()) {
                        id = c1.getInt(c1.getColumnIndex("id"));
                    }
                    c1.close();
                }

                alert_position = id;
                userAdapter.notifyItemChanged(alert_position);
            }
            else
                Toast.makeText(Security.this, ServerResponse, Toast.LENGTH_SHORT).show();
        }},
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError volleyError) {
                  //  Toast.makeText(Security.this, volleyError.toString(), Toast.LENGTH_SHORT).show();
                }
            })
    {
        @Override
        protected Map<String, String> getParams()
        {
            Map<String, String> params = new HashMap<>();
            params.put("email", email);
            return params;
        }};

    requestQueue.add(stringRequest);        // Adding the StringRequest object into requestQueue.
}

Kindly suggest some workaround to achieve the desired output of updating the colors of all 3 cards.

Answer 1

Got the solution. The same can be achieved by adding positions to Arraylist and then further calling that ArrayList via a for loop within the Recyclerview adapter class by iteration.

 if (tokens[0].equals("1")) {
                     power_position.add(id);
                     userAdapter.notifyDataSetChanged();
                 }

And within the Recyclerview adapter class.

for (int i=0; i<Security.alert_position.size(); i++) {
        if (position == Security.alert_position.get(i)) {
            holder.state.setText("< Data Changed >");
            holder.state.setTextColor(Color.RED);
            holder.cards.setBackgroundColor(0x33FF0000);
        }
    }

This will refresh the Recyclerview at once rather than calling individual recycler view items for updates.

Answer 2

1. I would use a ListAdapter<T, K> (from RecyclerView).
2. During the Cursor iteration, I would create (or modify) a new List based on the new values.
3. I would then submit a new list to the adapter (ListAdapter has a method called submitList(T).

Since you need to provide a "Diff Util" callback to the ListAdapter, it will take care of rebinding the views whose data has changed.

If you really want "real-time" one by one changing, then you'd need to dive deeper into having a ViewModel expose a state (perhaps a Flow) that you can observe and react to each emit(...).

There are alternatives here, but I would try the ListAdapter first, it's included in Android, and would likely work fine.

If you need help setting up a List Adapter, and because I've been asked this question over 9000 times, I have created the simplest recycler view sample over at GitHub I can imagine :)

Answer 3

calls to notifyItemChanged() are not synchronous, i.e. onBindViewHolder() will be called at a later time. By the time onBindViewHolder() is called, the static property Security.alert_position contains the newest value (from the 3rd time through the loop).

Recommendations:

Add Log statements to your call to notifyItemChanged() and onBindViewHolder(). You'll likely see that notifyItemChanged() calls precede the calls to onBindViewHolder(). Log the position and Security.alert_position values in onBindViewHolder(), this should explain why you're seeing what you're seeing.

Log.d("MY-TAG", String.format("calling notifyItemChanged(%d)", alert_position));

in onBindViewHolder()

Log.d("MY-TAG", String.format("onBindViewHolder(%d), Security.alert_position=%d", position, Security.alert_position));

I suspect you'll see the three calls to onBindViewHolder() showing correct position values (1,2,3), but Security.alert_position will always be 3.

While this recommendation won't solve your program logic, it will hopefully help you understand what's occurring.