实时数据库事务

Question

我一直试图运行事务方法，但它无法在firebase数据库中获取和设置正确的数据。

代码如下：

 private void receiveMoney() {
    String mobile=recipientText.getText().toString().trim();
    Double amount=Double.parseDouble(amountText.getText().toString().trim());
    mDatabase3=FirebaseDatabase.getInstance().getReference("account_details/Gn2eRixQQiTpvhX870n6nZp66tO2");
    mDatabase3.runTransaction(new Transaction.Handler() {

        @NonNull
        @Override
        public Transaction.Result doTransaction(@NonNull MutableData currentData) {

            Double newBalance=(double) currentData.child("initialBalance").getValue();
            System.out.println("Current Balance: "+newBalance+"  Amount: "+amount);

            currentData.setValue(newBalance);
            return Transaction.success(currentData);
        }

        @Override
        public void onComplete(@Nullable  DatabaseError error, boolean committed, @Nullable DataSnapshot currentData) {

        }
    });
}

E/RepoOperation: Caught Throwable.
java.lang.NullPointerException: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference
    at com.example.efikas.SendMoneyActivity$1.doTransaction(SendMoneyActivity.java:86)
    at com.google.firebase.database.core.Repo.startTransaction(Repo.java:933)
    at com.google.firebase.database.DatabaseReference$4.run(DatabaseReference.java:492)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:458)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
    at java.util.concurrent.ThreadPoolExecutor.processTask(ThreadPoolExecutor.java:1187)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    at java.lang.Thread.run(Thread.java:784)

Answer 1

我认为，因为您使用的是runtransaction，所以您应该只关注一件事。

mDatabase3=FirebaseDatabase.getInstance().getReference("account_details/Gn2eRixQQiTpvhX870n6nZp66tO2/initialBalance");
mDatabase3.runTransaction(new Transaction.Handler() {

    @NonNull
    @Override
    public Transaction.Result doTransaction(@NonNull MutableData currentData) {
        if (currentData.getValue() == null) {
            currentData.setValue(0);
        } else {
            Double newBalance= (Double) currentData.getValue();
            System.out.println("Current Balance: "+newBalance+"  Amount: "+amount);

            currentData.setValue(newBalance);
        }
        

        return Transaction.success(currentData);
    }

    @Override
    public void onComplete(@Nullable  DatabaseError error, boolean committed, @Nullable DataSnapshot currentData) {

    }
});