如何从 Firebase 实时数据库中检索所有手机的利润并对所有值求和

Question

I am creating an application of sale purchase I want to retrieve all the profit of sale mobiles and Sum the values to obtain the total earning.

    mDatabaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            List<Float> list = new ArrayList<>();
            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                list.add(Float.valueOf(Float.parseFloat(ds.child("profit").getValue().toString())));
                double sum = 0.0;
                for (Float d : list) {
                    double floatValue = (double) d.floatValue();
                    Double.isNaN(floatValue);
                    sum += floatValue;
                }
                Toast.makeText(RecordsActivity.this, "Earning = " + sum, Toast.LENGTH_SHORT).show();


            }
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            Toast.makeText(RecordsActivity.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
        }
    });

Answer 1

For starters I would suggest that you send profits to the database as ints. Then you can find the total sum of the figures under the nodes profits in a data snapshot as shown below

    @Override
    public void onDataChange(@NonNull DataSnapshot 
    dataSnapshot) {
    int sum=0;
    for (DataSnapshot ds1:dataSnapshot.getChildren()){
        int a=ds1.child("profit").getValue(Integer.class);
        sum+=b;
       int i = sum;
      String value = String.valueOf(i);
      Toast.makeText(RecordsActivity.this, value, 
      Toast .LENGTH_SHORT).show();
       }

       }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

}

});