Java Android - 访问 addValueEventListener 之外的变量

Question

我想知道如何在mDatabase.addValueEventListener之外访问变量totalAmount。

    //This is inside onCreateView
    mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            totalAmount=0;

            for (DataSnapshot mySnapshot : dataSnapshot.getChildren()){
                Transaction transaction = mySnapshot.getValue(Transaction.class);
                totalAmount += transaction.getAmount();
            }
            String total_amount = String.valueOf(totalAmount);
            totalAmount.setText(total_amount);
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
        }
    });

    TextView.setText(String.valueOf(totalAmount))

我找不到合适的解决方案。请帮我解决这个问题。

Answer 1

全局声明total_amount。请更改您的code，如下所示：

 String total_amount = ""
 mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            totalAmount=0;

            for (DataSnapshot mySnapshot : dataSnapshot.getChildren()){
                Transaction transaction = mySnapshot.getValue(Transaction.class);
                totalAmount += transaction.getAmount();
            }
            total_amount = String.valueOf(totalAmount);
            totalAmount.setText(total_amount);
        }
        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
        }
    });

    TextView.setText(total_amount)