Question

我目前正在尝试将Firebase数据库中的内容读取到RecyclerView，但我想将它们从最后一个节点加载到第一个节点。所以我决定将密钥放入一个数组，然后尝试从数组的末尾读到前面，但是当我尝试访问密钥数组时，出现Can't pass null for argument 'pathString' in child()错误。

以下是我用来加载数据的方法：

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

FirebaseRecyclerAdapter<UpcomingList, UpcomingViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<UpcomingList, UpcomingViewHolder>(
            UpcomingList.class,
            R.layout.upcoming_event_row,
            UpcomingViewHolder.class,
            mDatabase
    ) {
        @Override
        protected void populateViewHolder(final UpcomingViewHolder viewHolder, UpcomingList model, int position) {

            /*String CurrentString = date.toString().trim();
            StringTokenizer tokens = new StringTokenizer(CurrentString, "/");
            final String first = tokens.nextToken();
            final String second = tokens.nextToken();*/

            //final String post_key = getRef(position).getKey();
            mDatabase.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    int i = 0;
                    for (DataSnapshot d : dataSnapshot.getChildren()) {
                        key[i] = d.getKey();
                        i++;
                    }

                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });


            for (int counter = key.length - 1; counter >= 0; counter--) {
                viewHolder.setUpDate(first + "/" + key[counter]);
                mDatabase.child(key[counter]).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        StringBuilder builder = new StringBuilder();
                        for (DataSnapshot child : dataSnapshot.getChildren()) {
                            builder.append(child.getKey().toString() + "\n\n");

                        }
                        viewHolder.setName(builder.toString());
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
            }
        }

    };
    upcomingRV.setAdapter(firebaseRecyclerAdapter);
}

感谢您的协助。

Answer 1

你被异步编程101咬了。你需要确保需要key[]内容的代码是里面的一旦被调用的onDataChange钥匙已加载。

在这种情况下，这意味着它应该看起来像thisL

mDatabase.addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { int i = 0; for (DataSnapshot d : dataSnapshot.getChildren()) { key[i] = d.getKey(); i++; } for (int counter = key.length - 1; counter >= 0; counter--) { viewHolder.setUpDate(first + "/" + key[counter]); mDatabase.child(key[counter]).addValueEventListener(new ValueEventListener() { @Override public void onDataChange(DataSnapshot dataSnapshot) { StringBuilder builder = new StringBuilder(); for (DataSnapshot child : dataSnapshot.getChildren()) { builder.append(child.getKey().toString() + "\n\n"); } viewHolder.setName(builder.toString()); } @Override public void onCancelled(DatabaseError databaseError) { throw databaseError.toException(); // don't ignore errors } }); } } @Override public void onCancelled(DatabaseError databaseError) { throw databaseError.toException(); // don't ignore errors } });

在child（）中不能为参数'pathString'传递null

1 个答案: