在函数中执行Firestore查询时，需要确保已经对Firestore进行初始化，并且在查询结果返回之前等待异步操作完成。

示例代码：

private void loadDataFromFirestore() {
    FirebaseFirestore firestore = FirebaseFirestore.getInstance();
    CollectionReference myCollectionRef = firestore.collection("myCollection");

    // Example query
    Query myQuery = myCollectionRef.whereEqualTo("field", "value");

    myQuery.get().addOnSuccessListener(new OnSuccessListener() {
        @Override
        public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            // Your code to handle query results
        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            // Your code to handle query failure
        }
    });
}

如果在调用函数时遇到空查询结果的问题，可以尝试增加等待异步操作完成的代码：

public void myFunction() {
    // Initialize Firebase app
    FirebaseApp.initializeApp(this);

    // Load data from Firestore
    loadDataFromFirestore().addOnSuccessListener(new OnSuccessListener() {
        @Override
        public void onSuccess(Void aVoid) {
            // Do something with the data
        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            // Handle errors
        }
    });
}

private Task loadDataFromFirestore() {
    FirebaseFirestore firestore = FirebaseFirestore.getInstance();
    CollectionReference myCollectionRef = firestore.collection("myCollection");

    // Example query
    Query myQuery = myCollectionRef.whereEqualTo("field", "value");

    return myQuery.get().continueWith(new Continuation() {
        @Override
        public Void then(@NonNull Task task) throws Exception {
            if (task.isSuccessful()) {
                QuerySnapshot querySnapshot = task.getResult();
                // Your code to handle query results
            } else {
                // Your code to handle query failure
            }

            return null;
        }
    });
}