Android studio / Firebase - 試圖獲取數據的無限循環

Question

我正在嘗試從我的firebaseDB中獲取數據，但它一直在無限地進行，我看不出原因。

問題：用戶鍵入郵件來匯款。 我從數據庫中提取所有用戶，並將寫入的電子郵件與每個用戶的電子郵件進行比較。 如果電子郵件與用戶匹配（電子郵件是唯一的），則在內部進行另一次數據庫調用，獲取收件人的余額。 用戶的余額已更新，收件人也是如此。 問題是它不斷減去發件人的金額，並不斷為收件人添加（通過點擊一次）。

我知道這與異步執行有關，但我對編程很新，不知道如何解決它。

有人可以幫忙嗎？ 代碼如下：

    public void sendTo(){

    final String receiverEmail = editTextReciever.getText().toString().trim();
    String amountHolder = ediTextAmount.getText().toString().trim();

    if(TextUtils.isEmpty(receiverEmail)){
        Toast.makeText(getApplicationContext(), "Enter an email", Toast.LENGTH_LONG).show();
        return;
    }
    if(TextUtils.isEmpty(amountHolder)){
        Toast.makeText(getApplicationContext(), "Enter an amount to send", Toast.LENGTH_LONG).show();
        return;
    }

    //If it has gotten this far, theres data in the editText (the editText can only contain numbers)
    final int amount = Integer.parseInt(amountHolder);

    //Looping through every user in the DB and checking if the typed email belong to any of the users in the DB
    FirebaseDatabase.getInstance().getReference("users").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                User user = snapshot.getValue(User.class);
                //If typed email matches a user in the db (emails are unique due to firebaseAuthentication), continue
                if(user.getEmail().equals(receiverEmail)){

                    recipientUid = snapshot.getKey();
                    if(accountBalance - amount >= 0 && uid != snapshot.getKey()){
                        //I have to fetch our the balance of the user i'm sending money to so I can add the amount to his balance
                        FirebaseDatabase.getInstance().getReference("Accounts/" + accountType).child(snapshot.getKey()).child("balance").addValueEventListener(new ValueEventListener() {
                            @Override
                            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                                int balanceOfReceiver = Integer.parseInt(dataSnapshot.getValue().toString());
                                int updatedBalance = balanceOfReceiver + amount;
                                //The senders balance is updated
                                accountBalance = accountBalance - amount;
                                FirebaseDatabase.getInstance().getReference("Accounts/" + accountType).child(uid).child("balance").setValue(accountBalance);
                                //And the recipients balance is updated
                                FirebaseDatabase.getInstance().getReference("Accounts/" + accountType).child(recipientUid).child("balance").setValue(updatedBalance);
                            }
                            @Override
                            public void onCancelled(@NonNull DatabaseError databaseError) {

                            }
                        });
                    } else {
                        Toast.makeText(getApplicationContext(), "You can't overdraw or send money to yourself", Toast.LENGTH_LONG).show();
                    }
                }
            }
        }

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

        }
    });
}

Answer 1

您將ValueEventListener添加到用戶ref，並在數據更改時調用onDataChange。 你減去金額，再次觸發onDataChange然后你進入一個循環。

您需要重新考慮代碼結構或在更改金額之前刪除偵聽器。

這個

FirebaseDatabase.getInstance().getReference("Accounts/" + accountType).child(uid).child("balance").setValue(accountBalance);
FirebaseDatabase.getInstance().getReference("Accounts/" + accountType).child(recipientUid).child("balance").setValue(updatedBalance);

觸發這個

public void onDataChange(@NonNull DataSnapshot dataSnapshot)