Fix annoying Firebase ArrayList vs HashMap behaviour.

Firebase Realtime Database's snapshot.getValue(Class.class) will sometimes try to parse ArrayList in place where you'd expect to get a HashMap.

This function will convert all ArrayList occurences to HashMaps.

Example

You have a list of objects like this:

objects: {
    "5": { ... },
    "6": { ... },
    "8": { ... }
}

You might expect to get a HashMap<String, Object> that will hold object ids to their values. And you will.

But other times, you will have data like this:

objects: {
    "1": { ... },
    "2": { ... },
    "3": { ... }
}

And Firebase will convert this data to an ArrayList! (and element at index 0 will actually be null which is ridiculous).

To guarantee the consistency, I've decided to always convert data to a HashMap. Here's a real life example.

Get a hashmap object from the snapshot (or a child snapshot):

HashMap<Object, Object> obj = (HashMap<Object, Object>) snapshot.getValue();
FixFirebaseMap.fixFirebaseMap(obj);

Use GSON to convert your hashmap to a pojo.

Gson gson = new Gson();
JsonElement jsonElement = gson.toJsonTree(obj);
City city = gson.fromJson(jsonElement, City.class);

Installation

Just add this file to your project.

If you have any suggestions to my solution, please share.