如何从 firebase 数据库中获取一个孩子

Question

I have checked high and low but all I see are people trying to to get all the children into lists and stuff. I just want to get a single child from the database.

{
  "Haydn" : {
    "Users" : {
      "email" : "user@gmail.com",
      "name" : "kofi"
    }
  }
}

I want to get the name from the structure.

My code:

        rootNode = FirebaseDatabase.getInstance();
        reference = rootNode.getReference().child("Users");

        reference.addListenerForSingleValueEvent(
                new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        if(snapshot.exists()){
                            String displayName = (String) snapshot.child("Haydn").child("Users").child("name").getValue();
                            loggedInUserTextView.setText(displayName);
                        }
                    }

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

                    }
                }

Answer 1

You set up your reference like this:

reference = rootNode.getReference().child("Users");

That means that Firebase reads the data from /Users in your database. Since there is no Users node at the root of the JSON you posted, that means the snapshot you get is going to be empty.

---

To read a single node, as you're trying to do here, set up a reference to the exact path of that node:

reference = rootNode.getReference().child("Haydn/Users/name");

As you can see, you can pass the entire path to the node in the child(...) .

With this reference, you can then read the value like this:

reference.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        if(snapshot.exists()){
            String displayName = snapshot.getValue(String.class);
            loggedInUserTextView.setText(displayName);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException();
    }
}