不知道何时调用回收者视图动画以使其起作用

Question

我是android studio的新手，正在尝试制作一个recyclerView跌倒动画，但是我目前尚不清楚何时设置layoutAnimation。我正在使用Firebase回收器适配器。以下是我的OnViewCreated函数（public class EventsFragment extends Fragment）：

public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);
    final EditText inputSearch = (EditText) view.findViewById(R.id.inputSearch);
    inputSearch.addTextChangedListener(new TextWatcher() {

        // Implementing Search

    }
    ProductsRef = FirebaseDatabase.getInstance().getReference().child("Events");
    recyclerView = view.findViewById(R.id.event_recycler_menu);
    recyclerView.setHasFixedSize(true);
    layoutManager = new LinearLayoutManager(getActivity());
    recyclerView.setLayoutManager(layoutManager);
}

以下是OnStart函数：

@Override
public void onStart() {
    super.onStart();

    FirebaseRecyclerOptions<Events> options =
            new FirebaseRecyclerOptions.Builder<Events>().setQuery(ProductsRef , Events.class)
                    .build();

    FirebaseRecyclerAdapter<Events, EventViewHolder> adapter =
            new FirebaseRecyclerAdapter<Events, EventViewHolder>(options) {
                @Override
                protected void onBindViewHolder(@NonNull EventViewHolder holder, int position, @NonNull final Events model) {
                    holder.event_desc.setText(model.getDescription());
                    holder.event_loc.setText("Location :"+model.getLocation());
                    holder.event_time.setText("Time : "+model.getTime());

                    holder.itemView.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {
                            Intent intent = new Intent(getActivity(),EventDetailActivity.class);
                            intent.putExtra("eid",model.getEid());
                            startActivity(intent);
                        }
                    });
                }

                @NonNull
                @Override
                public EventViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
                    View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.event_user_layout, viewGroup,false);
                    EventViewHolder holder = new EventViewHolder(view);
                    return holder;
                }
            };
    recyclerView.setAdapter(adapter);
    adapter.startListening();
    runAnimation(recyclerView);
}

runAnimation函数如下：

private void runAnimation(RecyclerView recyclerView) {
    final Context context = recyclerView.getContext();
    final LayoutAnimationController controller = AnimationUtils.loadLayoutAnimation(context,R.anim.layout_falldown);
    recyclerView.setLayoutAnimation(controller);
    recyclerView.getAdapter().notifyDataSetChanged();
    recyclerView.scheduleLayoutAnimation();
}

设置适配器后，我试图调用runAnimation，但是动画根本不起作用。以下是我的 item_animation_fall_down.xml ：

<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:duration="@integer/animation_duration_medium">
<translate
    android:fromYDelta="-20%"
    android:toYDelta="0"
    android:interpolator="@android:anim/decelerate_interpolator"
    />
<alpha
    android:fromAlpha="0"
    android:toAlpha="1"
    android:interpolator="@android:anim/decelerate_interpolator"/>
<scale
    android:fromXScale="105%"
    android:fromYScale="105%"
    android:toXScale="100%"
    android:toYScale="100%"
    android:pivotX="50%"
    android:pivotY="50%"
    android:interpolator="@android:anim/decelerate_interpolator"/>
</set>

layout_falldown.xml ：

<?xml version="1.0" encoding="utf-8"?>
<layoutAnimation xmlns:android="http://schemas.android.com/apk/res/android"
    android:animation="@anim/item_animation_fall_down"
    android:delay="15%"
    android:animationOrder="normal">
</layoutAnimation>

请告诉我如何运行动画。运行动画的位置以及原因。