如何计算购物车中的总价？

Question

当用户按下添加按钮时，我的应用程序的购物车部分是离线实现的。产品存储在数据库中，然后显示在购物车中。

我的问题

更改商品的numberpicker后如何更改商品的价格？（一个数字的总价是从每个商品计算出来的，但是更改数字后，总价不变。）

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());
}

在数据库中显示

    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

你的问题是对象的引用。

您在 Adapter 中传递一个对象并在 Activity 上使用另一个对象。

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

并使用相同的数据库函数保存在帖子中

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

你可以做的是将posts= mydb.display();转移到适配器分配之上。

所以你的代码看起来像

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

现在添加按钮 onClickListener 在add() 之后使用您的setMealTotal()。

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

编辑

要更新您的总价，您需要在 FacultyList 以及您保存购物车数据的数据库上更改您的数量值。目前，您正在适配器 BindViewHolder 上手动更新 UI，不建议将其作为适配器的工作来根据绑定的数据更新 UI。使用 Recyclerview 检查 Android Room 或 CursorAdapter 以轻松执行这些任务。

目前您可以做的是创建一个界面来通知您的活动有关购物车中的更改。

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

在 CartActivity 上实现这个接口

@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()
}

并将 Activity 的引用传递给适配器。

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

现在在您的 Inc 和 Dcr 上调用此更新函数，如下所示

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);
               }
           }
       });