How to calculate total price when add/delete item in Android Studio

Question

I'm new in Android. I'm trying to create an e-commerce app. Currently, I'm creating add-to-cart activity. So, I've managed to add the item to cart and display in CartActivity. But the problem is, I don't know how to get the price and calculate the total price of all item. When I delete the item(i use onSwiped) the price not decreasing.

CartActivity

  public class CartActivity extends AppCompatActivity implements 
  RecyclerItemTouchHelper.RecyclerItemTouchHelperListener {
    private float totalcost=0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Log.d(TAG, "onDataChange: found a post id: babyyywhuu " + book_id);

    new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
        @Override
        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
            return false;
        }

        // Called when a user swipes left or right on a ViewHolder
        @Override
        public void onSwiped(RecyclerView.ViewHolder viewHolder, int swipeDir) {

            int position = viewHolder.getAdapterPosition(); // this is how you can get the position
            Book book= mAdapter.getItem(position); // You will have your own class ofcourse.

            DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
            reference.child("carts")
                    .child(FirebaseAuth.getInstance().getCurrentUser().getUid())
                    .child(book.getBook_id())
                    .removeValue();

        }
    }).attachToRecyclerView(recyclerView);
    init();

}


private void init(){
    Log.d(TAG, "init: initializing.");
    cartList = new ArrayList<>();
    setupPostsList();

    //reference for listening when items are added or removed from the watch list
     mDatabaseRef = FirebaseDatabase.getInstance().getReference()
            .child(getString(R.string.node_carts))
            .child(FirebaseAuth.getInstance().getCurrentUser().getUid());

    //set the listener to the reference
    mDatabaseRef.addValueEventListener(mLisenter);

}

private void getWatchListIds(){
    Log.d(TAG, "getWatchListIds: getting users watch list.");
    if(cartList != null){
        cartList.clear();
    }
    if(mPostsIds != null){
        mPostsIds.clear();
    }

    mPostsIds = new ArrayList<>();
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

    Query query = reference.child(getString(R.string.node_carts))
            .orderByKey()
            .equalTo(FirebaseAuth.getInstance().getCurrentUser().getUid());

    query.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if(dataSnapshot.getChildren().iterator().hasNext()){
                DataSnapshot singleSnapshot = dataSnapshot.getChildren().iterator().next();
                for(DataSnapshot snapshot: singleSnapshot.getChildren()){
                    String id = snapshot.child(getString(R.string.field_book_id)).getValue().toString();
                    Log.d(TAG, "onDataChange: found a post id: " + id);
                    mPostsIds.add(id);

                }
                getPosts();
            }else{
                getPosts();
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

private void getPosts(){
    if(mPostsIds.size() > 0){
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

        for(int i  = 0; i < mPostsIds.size(); i++){
            Log.d(TAG, "getPosts: getting post information for: " + mPostsIds.get(i));

            Query query = reference.child(getString(R.string.node_books))
                    .orderByKey()
                    .equalTo(mPostsIds.get(i));

            query.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    DataSnapshot singleSnapshot = dataSnapshot.getChildren().iterator().next();
                    Book book = singleSnapshot.getValue(Book.class);
                    Log.d(TAG, "onDataChange: found a post: " + book.getTitle());
                    cartList.add(book);
                    mAdapter = new CartListAdapter (CartActivity.this, cartList);
                    recyclerView.setAdapter(mAdapter);
here---->           totalcost += Float.parseFloat(book.getPrice());
                    String totPrice = Float.toString(totalcost);
                    TextView totPrice = findViewById(R.id.totalPrice);
                    totPrice.setText(totPrice);
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
    }
}
@Override
public void onResume() {
    super.onResume();
    cartList = new ArrayList<>();


}

/**
 * callback when recycler view is swiped
 * item will be removed on swiped
 * undo option will be provided in snackbar to restore the item
 */
@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction, int position) {
    if (viewHolder instanceof CartListAdapter.MyViewHolder) {
        // get the removed item name to display it in snack bar
        String name = cartList.get(viewHolder.getAdapterPosition()).getTitle();

        // backup of removed item for undo purpose
        final Book deletedItem = cartList.get(viewHolder.getAdapterPosition());
        final int deletedIndex = viewHolder.getAdapterPosition();

        // remove the item from recycler view
        mAdapter.removeItem(viewHolder.getAdapterPosition());

        // showing snack bar with Undo option
        Snackbar snackbar = Snackbar
                .make(linearlayour, name + " removed from cart!", Snackbar.LENGTH_LONG);
        snackbar.setAction("UNDO", new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                // undo is selected, restore the deleted item
                mAdapter.restoreItem(deletedItem, deletedIndex);

            }
        });
        snackbar.setActionTextColor(Color.YELLOW);
        snackbar.show();
    }
}

I've tried calculate it inside the getPosts() but I know it is completely wrong because the price keep on increasing. Do I have to create method to increase/decrease the method? Do you have any solutions to this? Thank you for your time.

Answer 1

There are 4 Cases where you have to update your price:-

1. Add a new item (maybe not used in your case only because you are on the cart page)
2. Delete item
3. Update quantity of item (increase or decrease quantity)
4. Applying any coupon code

Just create a new function and recalculate the total price, set to the text view and call just after adapter notifies or update adapter.

Answer 2

when you swipe to delete item from cart , try to get the item price and then subtract it from total amount :

int total_price = Integer.parseInt(totprice.getText().toString()) - theRemovedItemPrice ;
totprice.setText(String.valueOf(total_price) ;