How to sum checked items data values in RecyclerView

Question

My problem is how to sum all checked items values, and how to manage their changed at check/uncheck events? This is my method for check box toggle (check/uncheck) event.

holder.itemCheckBox.setOnClickListener(new View.OnClickListener() 
{
  @Override
  public void onClick(View v) 
  {
    if (((CheckBox) v).isChecked()) 
    {
      double price = Double.parseDouble(catalogDatabases.get(position).getPriceItem());
      holder.totalPrice = holder.totalPrice + price;
      holder.listener.respond(holder.totalPrice);
    } 
    else {
    }
  }
});

Are you talking about a List adapter ? Your purpose is to save the sum of all checked items ? — Rami Loiferman, Dec 27 '19 at 18:06
@afiq, Can you clear what is the problem you faced to do so? — Md. Asaduzzaman, Dec 27 '19 at 18:41
@RamiLoiferman i'm doing to sum all data when checked the box in my recyclerview. So how to sum all value is checked. that value take from position is selected and pass value to interface. — afiq, Dec 27 '19 at 18:46

Rami Loiferman · Accepted Answer · 2019-12-27T22:17:18.940

So first of all don't rely on the view as data. I'll explain in your code

if (((CheckBox) v).isChecked())

You relying on view's isChecked method. This may cause a bug because of android list recycling mechanism.

You can read about it in the link below
How ListView's recycling mechanism works

TL;DR views are being recycled so when you scroll your list. So for example the user checked item number 3 and then scrolled the list down item number 13 for example may also be shown as checked even tho it isn't .

So when onClick triggers we need to save the checked state in some list

After the theoretical intro i'll show it in code.

//Here you'll need to create some boolean array or list to store
//checked not checked positions lets call it checked
boolean[] checkedArr = new boolean[catalogDatabases.size()];
// catalogDatabases.size represents your data set size
// note that all items will be false initially

    @Override
    public void onBindViewHolder(@NonNull final MyViewHolder holder, final int position) {
        /**
         * Other views binding.......
         */
        holder.itemCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
                checkedArr[position] = isChecked;
                sumAllCheckedAndNotify();
            }
        }
        );
    }

(I decided to do the calculation on every check it more straight forward from making an update on the event)

    private void sumAllCheckedAndNotify() {
        double sum = 0;
        for (int i = 0; i < checkedArr.length; i++) {
            if(checkedArr[i]) {
                sum += Double.parseDouble(catalogDatabases.get(i).getPriceItem());
            }
        }
        // pudate the listener
        listener.respond(sum, selectedCount);
    }

notifyItemChanged is a build in method of list adapter https://stackoverflow.com/questions/32457406/how-to-update-refresh-specific-item-in-recyclerview — Rami Loiferman, Dec 27 '19 at 19:18
yes and boolean isChecked at second will error it because same at first name boolean so when i cange it will not use the second one — afiq, Dec 27 '19 at 19:26
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/204961/discussion-between-rami-loiferman-and-afiq). — Rami Loiferman, Dec 27 '19 at 19:29

Md. Asaduzzaman · Answer 2 · 2019-12-27T19:38:23.543

Store totalPrice inside adapter and add/subtract value based on CheckBox state like below:

class YourAdapter extends ... {

    double totalPrice = 0;

    ...

    @Override
    public void onBindViewHolder(@NonNull RecyclerHolder holder, int position) {

       holder.itemCheckBox.setChecked(catalogDatabases.get(position).isSelected());

       holder.itemCheckBox.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                double price = Double.parseDouble(catalogDatabases.get(position).getPriceItem());

                boolean isSelected = !catalogDatabases.get(position).isSelected();
                catalogDatabases.get(position).setSelected(isSelected);

                if (isSelected) {
                    totalPrice += price;
                } else {
                    totalPrice -= price;
                }

                holder.listener.respond(totalPrice);

                notifyDataSetChanged();
            }
        });
    }
}

Update your Model to hold checked/ unchecked state to persist data

class CatalogDatabase { //Assume this is your model class

    private boolean isSelected

    ....

    public boolean isSelected() {
        return isSelected;
    }

    public void setSelected(boolean selected) {
        isSelected = selected;
    }

    ....
}

((CheckBox) v).isChecked() can be incorrect because the list view recycling mechanism — Rami Loiferman, Dec 27 '19 at 19:07

How to sum checked items data values in RecyclerView

2 Answers2