Firebase监听器未被调用

Question

  

我想检查节点是否已创建。我刚刚在下面实现了Toa​​st，但没有任何敬酒。

注意：firebase DataBase现在为Total null

  DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

    reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Toast.makeText(RegisterActivity.this, dataSnapshot.getKey() + "", Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(RegisterActivity.this, databaseError.toString() + "", Toast.LENGTH_SHORT).show();
        }
    });

其次是我试过的代码，但没有运气

 DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

    reference.child("device_id");

    reference.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Toast.makeText(RegisterActivity.this, dataSnapshot.getKey() + "", Toast.LENGTH_SHORT).show();

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Toast.makeText(RegisterActivity.this, databaseError.toString() + "", Toast.LENGTH_SHORT).show();


        }
    });

Answer 1

更改此行代码：

${= ${Str} == ABC =}

使用：

reference.addListenerForSingleValueEvent(new ValueEventListener() {