Firebase-第三个子对象中的getValue返回null

Question

我有一个问题，当我想从Firebase获取值时，getValue()返回null

DataSnapshot appleSnapshot和DataSnapshot dataSnapshot-在控制台中，我也可以在Firebase中正确看到键和值

数据库结构

调试

DataSnapshot setting-返回键，但不返回值（空）

String settingKey-正确返回字符串键

String settingValue-返回空值

为什么我不能从较深的孩子那里获得价值？

private void readData(final ValidateJoinInterface validateJoinInterface, final String name, final String password, final String user) {

    DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
    ref.addListenerForSingleValueEvent(new ValueEventListener() {

        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot appleSnapshot : dataSnapshot.getChildren()) {

                DataSnapshot setting = appleSnapshot.child(name).child("Settings").child("Password");
                String settingKey = (String) appleSnapshot.child(name).child("Settings").child("Password").getKey();
                String settingValue = (String) appleSnapshot.child(name).child("Settings").child("Password").getValue();

            }
            validateJoinInterface.validateJoin(correctName, correctPassword, correctUserId);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            Log.e("DTAG", "onCancelled", databaseError.toException());
        }
    });
}

Answer 1

您可以获取任何值：

FirebaseDatabase.getInstance().getReference().child(name).child("Settings").child("Password")
                .addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        for (DataSnapshot messageSnapshot : dataSnapshot.getChildren()) {
                            Log.d(TAG,"KEY - "+messageSnapshot.getKey() + "VALUE - "+messageSnapshot.getValue());
                        }
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {
                        Crashlytics.logException(databaseError.toException());
                        sendMessageListener.onSendMessageFailure(databaseError.getMessage());
                    }
                });

Answer 2

假设name变量像您的示例Aa一样具有字符串值，并且假设Aa是Firebase根的直接子代，要解决此问题，请使用以下代码：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference settingsRef = rootRef.child(name).child("Settings");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
            String name = dataSnapshot.child("Name").getValue(String.class);
            String password = dataSnapshot.child("Password").getValue(String.class);
            Log.d("TAG", name + " / " + password);
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
settingsRef.addListenerForSingleValueEvent(valueEventListener);

输出将为：Aa / Aaa。