Firestore collection.get()完成操作后返回值

我正在运行类似于此问题中的问题的代码，我正在从每个文档中获取数组，并将其元素添加到全局ArrayList中.之后，在 collection.get()之外，我对该数组执行操作并返回.但是，如果我从onSuccess侦听器内Log.d全局ArrayList大小，它给出了正确的答案，但是如果我在collection.get()之外这样做，它总是给出0.我的问题是我不能从内部返回onSuccess，因为这不会为我的整个函数返回，因此我需要在未填充ArrayList的collection.get()之后执行此操作，大概是因为get()操作返回了 Task<> 这是一个异步操作，因此它不必等待它完成.这是我的代码:

I am running code similar to the problem in this question except, I am fetching arrays from each document and adding their elements to a global ArrayList. After that, outside of the collection.get(), I perform an operation on that array and return. However, If I Log.d the global ArrayList size from within the onSuccess listener, it gives the correct answer but if I do so outside of the collection.get() it always gives 0. My problem is that I cannot return from within the onSuccess because this will not return for my whole function and so I need to do it after the collection.get() where the ArrayList has not been populate, presumably since the get() operation returns a Task<> which is an asynchronous operation and so it doesn't wait for it to complete. Here is my code:

public static boolean Validator(final String sometext) {
    FirebaseFirestore db = FirebaseFirestore.getInstance();

    final ArrayList<String> mArrayList = new ArrayList<>();

    db.collection("my_collection").get()
        .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
            @Override
            public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                if (queryDocumentSnapshots.isEmpty()) {
                    Log.d(TAG, "Validator onSuccess: LIST EMPTY");
                    return;
                } else {

                    // Convert the Query Snapshot to a list of Document Snapshots, in this
                    // case, one document for each my_collection
                    List<DocumentSnapshot> my_collections = queryDocumentSnapshots.getDocuments();


                    for (int i = 0; i < my_collections.size(); i++) {
                        ArrayList<String> mArrayitems = (ArrayList<String>) my_collections.get(i).get("array");

                        for (int j = 0; j < mArrayitems.size(); j++) {
                            Log.d(TAG, "Adding array: " + mArrayitems.get(j).toString());
                            mArrayList.add(mArrayitems.get(j).toString());
                        }
                    }
                    Log.d(TAG, "Validator onSuccess: array list built");
                }
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.d(TAG, "Validator onFailure: " + e);
            }
        });

  // check if the given sometext matches a array in the list
  Log.d(TAG, "array list size: " + mArrayList.size());
  if (mArrayList.size() > 0) {
    for (int i = 0; i < mArrayList.size(); i++) {
        if (sometext.endsWith(mArrayList.get(i))) {
            return true
        }
      }
   }
   return false;
 }

我正在尝试通过一个类似于以下内容的回调来做到这一点:

I'm trying to do this with a callback which looks like:

// constructor
public Validator(String sometext) {
    this.valid = false;
    this.sometext = sometext
}

public interface myCallback{
    void onCallback(boolean valid);
}

public boolean validate() {

  readData(new MyCallback() {
        @Override
        public void onCallback(boolean valid) {
            setValid(valid);
        }
    });
  return this.valid;
 }

private void readData(final MyCallback myCallback) {
    FirebaseFirestore db = FirebaseFirestore.getInstance();

    db.collection("my_collection").get()
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                @Override
                public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                    if (queryDocumentSnapshots.isEmpty()) {
                        Log.d(TAG, "Validator onSuccess: LIST EMPTY");
                    } else {

                        List<DocumentSnapshot> my_collections = queryDocumentSnapshots.getDocuments();

                        ArrayList<String> mArrayList = new ArrayList<>();

                        for (int i = 0; i < my_collections.size(); i++) {
                            ArrayList<String> mArrayItems = (ArrayList<String>) my_collections.get(i).get("array");
                            for (int j = 0; j < mArrayItems.size(); j++) {
                                Log.d(TAG, "Adding array: " + mArrayItems.get(j).toString());
                                mArrayList.add(mArrayItems.get(j).toString());
                            }
                        }

                        boolean result = false;

                        Log.d(TAG, "array list size: " + mArrayList.size());
                        if (mArrayList.size() > 0) {
                            for (int i = 0; i < mArrayList.size(); i++) {
                                if (sometext.endsWith(mArrayList.get(i))) {
                                    result = true;
                                    Log.d(TAG, "MATCH FOUND");
                                    break;
                                }
                            }
                        }

                        myCallback.onCallback(result);

                    }
                }
            })
            .addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    Log.d(TAG, "Validator onFailure: " + e);
                }
            });
}

我遇到的问题是在validate()中，我想在回调完成后返回正确的有效值，因为它当前在回调完成之前返回了不正确的值.

The problem I'm having is that in validate() I want to return the correct valid value after the callback is finished because it currently returns the incorrect value before the callback has finished.