Question

所以在我的for循环中，我从一个路径中检索值，然后在查询中，我从第一个for循环中使用creatorUid从另一个路径中获取其他字符串。我需要找到一种方法来检索这些字符串并将它们添加到位于第一个for循环中但不是嵌套的for循环中的arraylist中。如果您需要澄清我在说什么，请在下面的代码中添加注释：

databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            chatsItemArrayList.clear();

            for (DataSnapshot ds : dataSnapshot.getChildren()) {
                title = "" + ds.child("title").getValue();
                description = "" + ds.child("description").getValue();
                date = "" + ds.child("datecreated").getValue();
                speaks = "" + ds.child("speaks").getValue();
                upvotes = "" + ds.child("upvotes").getValue();
                views = "" + ds.child("views").getValue();
                picture = "" + ds.child("chatpicture").getValue();
                String identifier = "" + ds.child("identifier").getValue();
                creatorUid = "" + ds.child("chatcreatoruid").getValue();

                System.out.println(creatorUid + " THIS IS THE CREATOR UID");


                Query query = FirebaseDatabase.getInstance().getReference().child("Users").orderByKey().equalTo(creatorUid);
                query.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {

                          //HOW DO I GET THESE VALUES FROM HERE:

                            rank = "" + dataSnapshot1.child("rank").getValue();
                            profilePicture = "" + dataSnapshot1.child("image").getValue();
                            username = "" + dataSnapshot1.child("username").getValue();

                            System.out.println("THIS IS THE RANK " + getRankText() + " THE USERNAME " + getUsernameText() + " PROFILEPICTURE " + getProfilePicture());

                        }
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {

                    }
                });

                System.out.println("R1" + getRankText() + " U1" + getUsernameText() + " P1 " + getProfilePicture());

                 // TO HERE:

                chatsItemArrayList.add(new ChatsItem(getProfilePicture(), title, date, speaks, description, getUsernameText(), getRankText(), upvotes, views, picture));

            }

            mAdapter = new ChatsFragmentAdapter(chatsItemArrayList);
            mRecyclerView.setAdapter(mAdapter);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

Answer 1

Firebase中的数据仅在onDataChange方法内部或从那里调用的代码中可用。没有解决方法。

如果需要其他数据库调用来加载其他数据，则应该：

要么先不添加项目，然后再将其添加到内部onDataChange
或首先将不完整的项目添加到列表中，然后在内部onDataChange

因此，最简单的修复方法是先执行以下操作：

query.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
            rank = "" + dataSnapshot1.child("rank").getValue();
            profilePicture = "" + dataSnapshot1.child("image").getValue();
            username = "" + dataSnapshot1.child("username").getValue();

            chatsItemArrayList.add(new ChatsItem(getProfilePicture(), title, date, speaks, description, getUsernameText(), getRankText(), upvotes, views, picture));

        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException();
    }
});

您通常还希望通过调用onDataChange之类的内部adapter.notifyDataSetChanged()方法刷新适配器。

另请参阅：

getContactsFromFirebase() method return an empty list
Wait Firebase async retrieve data in Android
Only load layout when firebase calls are complete
还有this list

如何从用于addValueEventListener

1 个答案: