android – 知道Firebase何时完成API调用？

当我的Firebase API调用完成时,我有些麻烦.阅读Firebase文档后,我发现以下内容：

Value events are always triggered last and are guaranteed to contain updates from any other events which occurred before that snapshot was taken.

我理解这一点意味着只有在所有的onChildAdded调用完成之后,才会调用ValueEventListener.因此,我想我可以在onChildAdded函数中填充RecyclerView,然后在onSingleValueListener调用中填充我的RecyclerView,我可以简单地完成动画加载屏幕(已经开始在此函数调用之前进行动画化)并继续.但是,我遇到了一个问题,在这里我放了一些细节的System.out.println语句,发现在我的情况下,测试1被调用之前测试2被调用.这会导致问题,因为这实际上是我想要的相反的行为：我想要onChildAdded函数完成,然后调用打印出Test 1被调用的onSingleValueListener函数.有什么原因造成这种情况吗？这样吗？我会很乐意解释为什么会发生这种情况.谢谢！

public void getComments(final String postId,final Activity activity,final View fragmentView,final View progressOverlay) {
    final Firebase commentsRef = firebaseRef.child("/comments");
    Firebase linkRef = firebaseRef.child("/posts/" + postId);
    linkRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            System.out.println("Test 1");
            if (progressOverlay.getVisibility() == View.VISIBLE) {
                progressOverlay.setVisibility(View.GONE);
                AndroidUtils.animateView(progressOverlay,View.GONE,200);
                fragmentView.findViewById(R.id.rv_view_comments).setVisibility(View.VISIBLE);
            }
        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
    linkRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot,String s) {
            commentsRef.child(dataSnapshot.getKey()).addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    Comment comment = dataSnapshot.getValue(Comment.class);
                    System.out.println("Test 2");
                    application.getCommentsRecyclerViewAdapter().getCommentsList().add(comment);
                    application.getCommentsRecyclerViewAdapter().notifyDataSetChanged();
                }

                @Override
                public void onCancelled(FirebaseError firebaseError) {

                }
            });
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot,String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot,String s) {

        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });
}

解决方法

使用此代码“Firebase linkRef = firebaseRef.child(”/ posts /“postId);”我可以看到您使用的是旧版Firebase API.现在已经弃用了

请将您的代码更新为新的Firebase 3.x.x API.

下面两个是独立的异步调用;根据用例,您可以使用其中一个侦听器来读取数据.

1. linkRef.addListenerForSingleValueEvent(new ValueEventListener() {});
2. linkRef.addChildEventListener(new ChildEventListener() {});

您可以参考firebase文档来获取有关数据库侦听器的更多信息.
https://firebase.google.com/docs/database/android/retrieve-data

使用以下代码段,您可以检索并填充您的注释列表.

public void getComments(final String postId,final View progressOverlay) {
    DatabaseReference commentsRef = firebaseRef.child("/comments");
    DatabaseReference linkRef = commentsRef.child("/posts/" + postId);
    linkRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            // Iterate through data-snapshot,and update your Adapter dataset
            for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                Comment comment = snapshot.getValue(Comment.class);
                application.getCommentsRecyclerViewAdapter().getCommentsList().add(comment);
            }
            application.getCommentsRecyclerViewAdapter().notifyDataSetChanged();

            // Dismiss your loading progressbar
            if (progressOverlay.getVisibility() == View.VISIBLE) {
                progressOverlay.setVisibility(View.GONE);
                AndroidUtils.animateView(progressOverlay,200);
                fragmentView.findViewById(R.id.rv_view_comments).setVisibility(View.VISIBLE);
            }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            // Handle fail case here
        }
    });

希望这会帮助你！