Recyclerview 适配器：java.util.ArrayList 无法强制转换为 com.google.ZBF12E1525C25C7AB9A15com.google.ZBF12E1525C25C7AB9A15Z.firestore.F1413SnapshotA15查询

Question

I'm fairly new and I'm not familiar with using recyclerview adapter. I have this method to to load the data into the recyclerview adapter. The data will be filtered using merged queries. However the app crashed and I got java.lang.ClassCastException: java.util.ArrayList cannot be cast to com.google.firebase.firestore.QuerySnapshot. Does anyone know how to fix this?

private void loadData(){

        if(modelArrayList.size()>0)
            modelArrayList.clear();

        storageReference = FirebaseStorage.getInstance().getReference();
        Query query = collectionReference.whereArrayContains("pet", pettype);
        Query query2 = collectionReference.whereArrayContains("service", "Pet Sitting");
        Query query3 = collectionReference.whereArrayContains("petnum", petnumber);
        Query query4 = collectionReference.whereArrayContains("region", reg);
        Query query5 = collectionReference.whereArrayContains("subregion", subreg);

        Task task = query.get();
        Task task2 = query2.get();
        Task task3 = query3.get();
        Task task4 = query4.get();
        Task task5 = query5.get();

        Task combinedtask = Tasks.whenAllSuccess(task, task2, task3, task4, task5);

        combinedtask.addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                for(DocumentSnapshot querySnapshot: task.getResult()){
                    model model = new model(querySnapshot.getString("firstname"),
                            querySnapshot.getString("lastname"),
                            querySnapshot.getString("description"),
                            querySnapshot.getString("userID"));

                    modelArrayList.add(model);
                }
                adapter = new My_recyclerview_adapter(Pet_sitting_result.this, modelArrayList);
                recycler_view.setAdapter(adapter);
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(Pet_sitting_result.this, "Error", Toast.LENGTH_SHORT);
            }
        });
    }

Answer 1

Since your combinedTask is a result of several other Tasks, it is going to yield an List objects as a result, not a QuerySnapshot . So, your success callback should declare that it accepts a List<Task<?>> instead of a Task<QuerySnapshot> . There will be one item the list for each task you passed to whenAllSuccess() . You will have to write code to pull the individual snapshots for each query out of the list and deal with them each separately as needed.

You might want to familiarize yourself more with the Tasks API that you're using here and also study the API documentation for Tasks.whenAll() .