如何从Firebase数据库中的子项成功计算值

Question

我正在尝试计算数据库中所有名为“价格”的子项的价值总和

下面是我的代码

@Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        mtotal = (TextView) findViewById(R.id.textre);
        mda = FirebaseDatabase.getInstance().getReference().child("Cart");
        mda.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                int sum = 0;
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    Map<String, Object> map = (Map<String, Object>) ds.getValue();
                    Object price = map.get("Price");
                    int pvalue = Integer.parseInt(String.valueOf(price));
                    sum += pvalue;
                    if (sum<100){
                        Toast.makeText(getApplicationContext(),"greare",Toast.LENGTH_SHORT).show();
                    }else {
                        Toast.makeText(getApplicationContext(),"sorry",Toast.LENGTH_SHORT).show();
                    }

                }


            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.d(TAG, databaseError.getMessage());

            }
        });

如我的代码所示，如​​果从价格节点获得的值小于100，则应该显示一条吐司消息，说“成功”。相反，该应用程序崩溃时没有任何消息

图像是我的Firebase数据库的视图，显示了我希望获取的值“ Price”

Answer 1

尝试执行此操作，我认为您没有正确获得Price值

mda.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            int sum = 0;
            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                int pvalue = ds.child("Price").getValue(Integer.class);
                sum += pvalue;
                if (sum<100){
                    Toast.makeText(getApplicationContext(),"greare",Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(getApplicationContext(),"sorry",Toast.LENGTH_SHORT).show();
                }

            }


        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Log.d(TAG, databaseError.getMessage());

        }
    });