Read arrays from Firestore and put them inside an ArrayList - Java in Android Studio

Question

I'm trying to create an application that can read the values from a Firestore array and put them into an ArrayList or something, this is my code:

    ArrayList<Integer> driverPermissions = new ArrayList<>();

    Firestore.collection("Admins").document("1234567890").get().addOnCompleteListener(task -> {
        DocumentSnapshot document = task.getResult();
        driverPermissions = document.get("Test");
    });

Unfortunately, it doesn't work. It marks me as an error in this line:

driverPermissions = document.get("Test");

And the error is:

Variable used in lambda expression should be final or effectively final

How can I add the values present inside the array on Firestore into an ArrayList or something like that and then use that throughout the code? And not only within the method?

Answer 1

Try This

 driverPermissions = document.getString("Test");

Answer 2

Your trying to get data type String but You declared Array tn Integer first mistake.

Then try this

Firestore.collection("Admins").document("1234567890").get().
addOnCompleteListener(task -> {
    DocumentSnapshot document = task.getResult();
   ArrayList<String> driverPermissions = (ArrayList<String>) 
   document.get("Test");
});

Here you can store only store string type data.

Or you can try like this

ArrayList<Object> driverPermissions = New ArrayList<>();

Firestore.collection("Admins").document("1234567890").get().
addOnCompleteListener(task -> {
    DocumentSnapshot document = task.getResult();
   driverPermissions.add(new String(document.get("Test")); // When Storing STring
driverPermissions.add(new Integer(document.get("Test")); // When Storing Integer

});

Here you can store any kind of data can be integer can be string But You have to declared what kind of data your storing.

Answer 3

A variable that is used in a lambda expression should always be final or effectively final , and you cannot change that. To solve this, you either make the variable a member of the class or define it and initialize it inside the onComplete() .

How can I add the values present inside the array on Firestore into an ArrayList or something like that and then use that throughout the code? And not only within the method?

There is no way you can do that . Firebase API is asynchronous, meaning that any code that needs data from Cloud Firestore, needs to be inside the onComplete() method, or be called from there. You cannot simply use it outside the callback, even if the field is a member of the class. So to solve this you can use a custom callback as seen in that answer. The reason is that you need to wait for the data. If you understand Kotlin, you might also be interested in reading the following resource:

• How to read data from Cloud Firestore using get()?

In Java, you should consider using LiveData . I think thisrepo might also help.

PS If you need at some point in time to use an array of objects, here is another helpful resoruce:

• How to map an array of objects from Cloud Firestore to a List of objects?