如何计算购物车中的总价？

Question

The shopping cart section of my app is implemented offline when the user presses the add button. The product is stored in the database and then displayed in the shopping cart.

my question

How can I change the price of products after changing the numberpicker of products?(The total price of a number is calculated from each product, but after changing the number, the total price does not change.)

cartadapter.java

public class FacultyAdapter extends RecyclerView.Adapter<FacultyAdapter.FacultyViewHolder> {

dbhandler mydb;
private int counter=1;
private Context context;
private List<Faculty> facultyList;
Faculty faculty ;

public FacultyAdapter(Context context, List<Faculty> facultyList) {
    this.context = context;
    this.facultyList=facultyList;
}

@NonNull
@Override
public FacultyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

    View view = LayoutInflater.from(context).inflate(R.layout.itemcard,parent,false);
    RecyclerView.LayoutParams lp = new RecyclerView.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, 
   ViewGroup.LayoutParams.WRAP_CONTENT);
    view.setLayoutParams(lp);

    return new FacultyViewHolder(view);
}


   /////////////////////////////////////////////////
 @Override
 public void onBindViewHolder(@NonNull final FacultyViewHolder holder,final int position) {

     faculty = facultyList.get(position);
    holder.title.setText(faculty.getName());
   holder.price.setText(faculty.getPrice());
   holder.count.setText(String.valueOf(faculty.getQty()));
   holder.inc.setGravity(Gravity.CENTER);
    String photoname=faculty.getImage();
    Glide
            .with(context)
            .load( Urls.image+photoname)
            .placeholder(R.mipmap.ic_launcher_round)
            .error(R.drawable.logo)
           .into(holder.img);

    mydb=new dbhandler(context);


         //////////////////////////////////
    holder.inc.setOnClickListener(new View.OnClickListener() {
       @Override
       public void onClick(View v) {
           int count= Integer.parseInt(String.valueOf(holder.count.getText()));
           count++;
           holder.count.setText(String.valueOf(count));
            faculty.setQty(count);
        Log.d("inc",""+faculty.getQty());
       }
   });
    holder.dec.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int count= Integer.parseInt(String.valueOf(holder.count.getText()));
            if(count>1){
                count--;
                holder.count.setText(String.valueOf(count));
                faculty.setQty(count);
              //  Log.d("dec",""+count);
            }
        }
    });
}
 ///////////////////////////////////
@Override
public int getItemCount() {
    return facultyList.size();
}
 ////////////////////////////////
public class FacultyViewHolder extends RecyclerView.ViewHolder {

    TextView title;
    TextView price,count;
   ImageView img;
    CardView card,viewBackground;

 Button inc,dec;
    private FacultyViewHolder(View itemView) {
        super(itemView);
        title = itemView.findViewById(R.id.txt_list_item_title);
        price = itemView.findViewById(R.id.txt_list_item_des);  
       img=itemView.findViewById(R.id.image_cart);
        inc=itemView.findViewById(R.id.increment);
        dec=itemView.findViewById(R.id.decrement);
        count=itemView.findViewById(R.id.display);
        card =itemView.findViewById(R.id.card);
        viewBackground =itemView.findViewById(R.id.view_background);
    }
}

//////////////////////////////////////////
public void remove(int position){
    final Faculty s = facultyList.get(position);
    facultyList.remove(position);
    String e=s.getId().toString();
    mydb.delete(e);
    notifyItemRemoved(position);
}

}

cartactivity.java

 public class cart extends AppCompatActivity implements 
  RecyclerItemTouchHelper.RecyclerItemTouchHelperListener {
Button Add,total; 
ImageButton back_btn;
Faculty items;
private TextView price_total; 
FacultyAdapter facultyAdapter;
dbhandler mydb;
String name;
 List<Faculty> posts;
String id, title, status, price, image,sum;
@SuppressLint("WrongConstant")
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_cart);

    RecyclerView recyclerView = findViewById(R.id.rv_card);
    Add = findViewById(R.id.btn_basket_pay);
    price_total = findViewById(R.id.totalPrice);
    mydb=new dbhandler(getApplicationContext());
    back_btn=findViewById(R.id.back);
    total=findViewById(R.id.total);

   mydb.open();

    facultyAdapter = new FacultyAdapter(getApplicationContext(), mydb.display());
    recyclerView.setLayoutManager(new LinearLayoutManager(getApplicationContext(), 
   LinearLayoutManager.VERTICAL, false));
    recyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(facultyAdapter);  

   facultyAdapter.registerAdapterDataObserver(observer);
    posts= mydb.display();

    for (int i= 0; i < posts.size(); i++){
       facultyAdapter.calculateTotalF(i);      
        name=""+posts.get(i).getName();
    }

    items = new Faculty(id,title, status, price, sum);
    SharedPreferences preferences = getSharedPreferences("prefs",MODE_PRIVATE);
    facultyAdapter.notifyDataSetChanged();
    items.setSum(String.valueOf(price_total.getText()));

    //////////////////////////////////
    mydb.close();

    total.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
          //  price_total.setText(""+ bundle.getString(qty_dkey));
        }
    });
       ////////////////////////////////////////////////
    back_btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            startActivity(new Intent(cart.this, MainActivity.class));
            finish();
        }
    });
      //////////////////////////
    ItemTouchHelper.SimpleCallback simpleCallback=new RecyclerItemTouchHelper(0,ItemTouchHelper.LEFT 
   |ItemTouchHelper.RIGHT,this);
    new ItemTouchHelper(simpleCallback).attachToRecyclerView(recyclerView);
    //////////////////////////////////////////////////
    Add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           add();
        }
    });
  }
  //////////////////////////////////////////////////////////////////////////
 public int calculateMealTotal(){
 int mealTotal = 0;
for(Faculty order : posts){
    mealTotal +=Integer.parseInt(order.getPrice()) * order.getQty();
    Log.d("qtyad",""+order.getQty());
    Log.d(" mealTotal",""+ mealTotal);
}

return mealTotal;
}

RecyclerView.AdapterDataObserver observer = new RecyclerView.AdapterDataObserver() {
    @Override
    public void onChanged() {
        super.onChanged();
        setMealTotal();
        Log.d("ob","ob");

    }
};
public void setMealTotal(){
    price_total.setText(" "+ calculateMealTotal());
}

display in database

    public List<Faculty> display(){

    SQLiteDatabase db = this.getReadableDatabase();
    String selectQuery = "SELECT  * FROM " + TBL_NAME ;
    Cursor cursor = db.rawQuery(selectQuery, null);

    if (cursor!= null)
        cursor.moveToFirst();
    List<Faculty> facultyList = new ArrayList<>();
    try {
        do{

            Faculty faculty = new Faculty(id,title, status, price, image);
            faculty.setId(cursor.getString(0));
            faculty.setName(cursor.getString(1));
            faculty.setPrice(cursor.getString(3));
            faculty.setQty(cursor.getInt(4));
            faculty.setImage(cursor.getString(2));
            // faculty.setQty(cursor.getString(3));
            facultyList.add(faculty);
        }while (cursor.moveToNext());

    } catch (Exception e) {
        e.printStackTrace();
    }

    return facultyList;
}

Answer 1

Your issue is the reference of the object.

You are passing one object in Adapter and using another on Activity.

facultyAdapter = new FacultyAdapter(getApplicationContext(), mydb.display()); //one object

and saving in post using same db function

 posts= mydb.display(); //creates another object

What you can do is shift posts= mydb.display(); above adapter assignment.

So your code look like

posts= mydb.display();
facultyAdapter = new FacultyAdapter(getApplicationContext(), posts);

Now on Add button onClickListener use your setMealTotal() after add() .

Add.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
           add();
           setMealTotal()
        }
});

EDIT

For updating your total price you need change the values of your quantity on FacultyList and also on the DB where you are saving the cart data. Currently you are updating the UI manually on adapter BindViewHolder which is not recommended as its the job of an adapter to update the UI according to the data with which it is binded. Check Android Room or CursorAdpter with Recyclerview to easily perform these task.

Currently what you can do is create an interface to notify your activity about the changes in your cart.

interface ICartModification{
  void increment(int qty, Faculty faculty)
  void decrement(int qty, Faculty faculty)
} 

Implement this interface on CartActivity

@Overrides
void increment(int qty, Faculty faculty){
   faculty.setQty(qty)

    //update DB here
   facultyAdapter.notifyDataSetChanged()
   setMealTotal()
}
@Overrides
void decrement(int qty, Faculty faculty){
   if(qty<=0)
      posts.remove(faculty)
   else
      faculty.setQty(qty)

   //update DB here
   facultyAdapter.notifyDataSetChanged()
   setMealTotal()
}

and pass reference of Activity to adapter.

facultyAdapter = new FacultyAdapter(this, mydb.display());

Now on your Inc and Dcr call this update function as follows

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

           if(context instanceof ICartModification){
               ((ICartModification)context).increment(faculty.getQty()+1, faculty);
           }
       }
   });

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

               if(context instanceof ICartModification){
                   ((ICartModification)context).decrement(faculty.getQty()-1, faculty);
               }
           }
       });