FireBase Query. DataSnapshot

Question

I need help on getting the \"message\" Object from this DataSnapshot result

DataSnapshot { key = user-4, value = {-JvFuwKX7r7o0ThXc0x8={sender=unit_owner, messag         


        

Answer 1

I looks like you're adding a value listener to something that has multiple children. I'm guessing it's a limitToLast(1) query, but it would be really helpful if you include the code in your question. Until you do add it however, this is my guess of what your code looks like:

Firebase ref = new Firebase("https://yours.firebaseio.com");
Query messages = ref.orderByKey().limitToLast(1);
messages.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        Log.i("Messages", dataSnapshot.toString());
    }

    @Override
    public void onCancelled(FirebaseError firebaseError) {

    }
})

While you are limiting the filter to single message, you are still a list of messages. It's just a list of only 1 message.

This means that on onDataChange you will still need to drill down into the child. Since you cannot do that by index, you will need to use a for loop:

public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot chatSnapshot: dataSnapshot.getChildren()) {
        String message = (String) chatSnapshot.child("message").getValue();
        String sender = (String) chatSnapshot.child("sender").getValue();
    }
}

Note that this gets a lot more readable if you take a moment to create a Java class that represents the message:

public class Chat {
    String message;
    String sender;
    public String getMessage() { return message; }
    public String getSender() { return sender; }
}

Then you can get the message with:

public void onDataChange(DataSnapshot dataSnapshot) {
    for (DataSnapshot chatSnapshot: dataSnapshot.getChildren()) {
        Chat chat = chatSnapshot.getValue(Chat.class);
        String message = chat.getMessage();
        String sender = chat.getSender();
    }
}

The above snippet still needs the for loop, since you're still getting a list of 1 messages. If you want to get rid of that loop, you can register a child event listener:

query.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        Chat chat = dataSnapshot.getValue(Chat.class);
        String message = chat.getMessage();
        String sender = chat.getSender();
    }

    // other overridden messages have been removed for brevity

})

Firebase will call the onChildAdded() method for each child, so you don't have to look over them yourself.

Answer 2

The value will be returned as an Object, as you've stated, but you can actually cast it to Map<String, Object> since you know it should be a map.

So, do something like this:

Map<String, Object> val = (Map<String, Object>) dataSnapshot.getValue();
String message = (String) val.get("message");
String sender = (String) val.get("sender");