Firebase数据库始终返回null

Question

从这个firebase数据库读取时，它总是返回null而不是我需要的值。

我试过用String.class以String的形式拉它但它仍然是null。

我需要从数据库中提取的只是int pName，在这种情况下dfdf变量将是final FirebaseDatabase aDatabase = FirebaseDatabase.getInstance(); final DatabaseReference mDatabase = aDatabase.getReference(); DatabaseReference myRef = aDatabase.getReference(pName).child("dose"); // Read from the database myRef.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { // This method is called once with the initial value and again // whenever data at this location is updated. Integer Value = dataSnapshot.getValue(Integer.class); String peter = Integer.toString(Value); count.setText(peter); } @Override public void onCancelled(DatabaseError error) { count.setText("E"); } });

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Answer 1

尝试更改 -

DatabaseReference myRef =  aDatabase.getReference(pName).child("dose");

到 -

DatabaseReference myRef =  mDatabase.child(pName).child("dose");

您应该在mDatabase上运行而不是在数据库上运行，并且不要让孩子参考

将听众改为

  

addListenerForSingleValueEvent

Answer 2

DatabaseReference myRef = mDatabase.child(pName).child("dose");

如上所述修复参考。

Answer 3

试试这段代码..

    private void readData(){
    final FirebaseDatabase aDatabase = FirebaseDatabase.getInstance();
    final DatabaseReference mDatabase = aDatabase.getReference();

   // Read from the database child() method put your database name
    mDatabase.child("dfdf").addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // This method is called once with the initial value and again
            // whenever data at this location is updated.
           // if i insert data as user class object then it give user.class
           // User user = dataSnapshot.getValue(User.class);

            Integer Value = dataSnapshot.getValue(Integer.class);
            String peter = Integer.toString(Value);
            count.setText(peter);
        }

        @Override
        public void onCancelled(DatabaseError error) {
            count.setText("E");
        }
    });
}

Answer 4

尝试以下方法：

DatabaseReference ref=FirebaseDatabase.getInstance().getReference().child("dfdf");
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    if(dataSnapshot.exists()){
  int value = dataSnapshot.child("dose").getValue(Integer.class);
    Log.i("Value is:", value);
  }
}

@Override
public void onCancelled(DatabaseError error) {
    count.setText("E");
  }
});

以上内容将检查快照dfdf是否存在然后进入onDataChange并检索子dose