Firebase Cloud Firestore：查询未更新 Android 中的 ArrayList

Question

I am using the following query:

db.collection("Example")
                .whereEqualTo("UserId", currentUser.getUid())
                .orderBy("timestamp", Query.Direction.ASCENDING)
                .get()
                .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()){
                            for (QueryDocumentSnapshot document : task.getResult()){
                                Log.i(TAG, "onComplete: " + document.get("UserId") + " => " + document.get("userText"));
                                userIdArrayList.add(document.get("UserId").toString());
                                userTextArrayList.add(document.get("userText").toString());

                            }
                        }else{
                            Log.i(TAG, "onComplete: Error getting documents", task.getException());
                        }
                    }
                });

As the query is iterating through results, I would like it to add the results to an array. However, when I run the code and attempt to print the content of the array list, I am getting and IndexOutOfBounds exception despite me looking at userTextArrayList.get(0); which should contain a result. I have added the line Log.i to check if the code is running successfully and I can see in the Logcat that the data is being pulled from the database. For some reason this code isn't adding the results to the ArrayList.

I'm not sure what else to try and I am unable to find anywhere in the documentation that can assist me with where I have potentially gone wrong.

Please feel free to point me towards the documentation that can assist with the problem if providing the answer is too much bother. I appreciate any guidance anyone can provide.

Thanks!

Edit: I am getting an error on the following lines of code:

1. userIdArrayList.add(document.get("UserId").toString());
2. userTextArrayList.add(document.get("userText").toString())

For some reason these lines aren't adding the data to the array and when I attempt to print the array later in the code (ie Log.i(TAG, "User Text => userTextArrayList.get(0).toString()); ), I am recieving and error for IndexOutOfBounds - apparently the ArrayList does not contain data despite the above code adding data to the ArrayLists.

Answer 1

You need to understand that this query is asynchronous and the results might not have yet been added to userTextArrayList when you execute this log statement Log.i(TAG, "User Text => userTextArrayList.get(0).toString());

This log statement needs to be in onComplete() as below in order for it to work:

@Override
public void onComplete(@NonNull Task<QuerySnapshot> task) {
    if (task.isSuccessful()) {
        for (QueryDocumentSnapshot document : task.getResult()) {
            Log.i(TAG, "onComplete: " + document.get("UserId") + " => " + document.get("userText"));            
            userIdArrayList.add(document.get("UserId").toString());      
            userTextArrayList.add(document.get("userText").toString());
        }
        yourButton.setEnabled(true);
    } else {
        Log.i(TAG, "onComplete: Error getting documents", task.getException());
        yourButton.setEnabled(false);
    }
 }