Cannot read data in Firebase Database as list

Question

The data in firebase is like the following

I want to get the data tagged as userId

Answer 1

The error message contains the gist of it:

Expected a List while deserializing, but got a class java.util.HashMap

If you look at your database, you see a collection of keys+values. In Java that translates to a Map and not to a List.

If you're only interested in the values, you need to handle the conversion from the Map to the List in your code:

public void onDataChange(DataSnapshot dataSnapshot) {
    GenericTypeIndicator> t = new GenericTypeIndicator>() {};
    Map map = dataSnapshot.getValue(t);

    // get the values from map.values();

Or simpler:

public void onDataChange(DataSnapshot dataSnapshot) {
    List list = new ArrayList();
    for (DataSnapshot child: dataSnapshot.getChildren()) {
        list.add(child.getValue(Friends.class));
    }
}