Firebase:嵌套循环结果不正常

Question

我想为Firebase数据做一个嵌套循环，但是结果是不正常的。我知道Firebase异步运行，但我不知道如何解决这个问题。请帮我解决这个问题。

守则：

public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_recommend, container, false);
    text = view.findViewById(R.id.test);
    fuser = FirebaseAuth.getInstance().getCurrentUser();

    getInfo();

    return view;
}

private void getInfo() {
    FirebaseDatabase.getInstance().getReference().child("users").addValueEventListener(new ValueEventListener() {

        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
                User user = dataSnapshot.getValue(User.class);
                assert user != null;
                System.out.println("user " + user.getId() + "");
                FirebaseDatabase.getInstance().getReference().child("Posts").addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {
                        for (DataSnapshot datasnapshot : snapshot.getChildren()) {
                            Post post = datasnapshot.getValue(Post.class);

                            System.out.println("posts " + post.getPostid() + "");

                        }
                    }

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

                    }
                });

            }

        }

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

        }
    });
}

结果：

I/System.out:用户3 JERhGpZ1IYGswKZNOTJGY7mAU 13

I/System.out:用户AiHsIMRL4zd9YkdkMEhY0MRhHDU2

I/System.out:用户EXmknYFLpqcAHcvbcIUJYSTtDdl1

I/System.out:用户KV4tUuczuUbWLz3DR0gLn8STmF73

I/System.out:用户Lg8eMt56NOOAXx5PAPrYrbVnE533

I/System.out:用户QOMfQ4Vhk6cOniAsj2YnMnxRP8W2

I/System.out:用户Tnd20qA2g6VPr9s69ziPjou8K113

I/System.out:用户YsJCUD3lq2OsVknxcRqOTQNGFpP2

I/System.out:用户c8QABIe3zxNIZRCCbpvkHMd138x2

I/System.out:用户pBfZlyWmGrc6h4bcLLl4Re4MHe53

I/System.out:用户rRHFEuawGsMoUDzrIUaycBKy5653

I/System.out:用户xUWVqIoBKsaM8eq9pm1ky0YGm5R2

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

职位-MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

I/System.out: posts MMpqMPistmQyGm-_NpM

I/System.out: posts -MNTf7Hf6Eo_uB_jTXuw

I/System.out: posts -MNTluR0nSJARQ_tosL0

在我的Firebase中，我有12个用户和3个帖子，所以System.out.println("posts "+post.getPostid()+"");打印了36次。我希望代码打印每个用户的三个帖子作为每个嵌套循环在同步工作，而不是打印所有用户，然后打印帖子，所以，如何解决呢？

Answer 1

一旦您给出了打印语句，就无法延迟它。因此，以正确的顺序获得输出的唯一方法是将print语句移动到您想要的数据可用的时候。

FirebaseDatabase.getInstance().getReference().child("users").addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot snapshot) {
        for (DataSnapshot dataSnapshot : snapshot.getChildren()) {
            User user = dataSnapshot.getValue(User.class);
            assert user != null;
            FirebaseDatabase.getInstance().getReference().child("Posts").addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot snapshot) {

                    System.out.println("user "+user.getId()+"");

                    for (DataSnapshot datasnapshot : snapshot.getChildren()) {
                        Post post = datasnapshot.getValue(Post.class);
                        System.out.println("posts "+post.getPostid()+"");
                    }
                }

                @Override
                public void onCancelled(@NonNull DatabaseError error) {
                    throw error.toException(); // don't ignore errors
                }
            });
        }
    }
    @Override
    public void onCancelled(@NonNull DatabaseError error) {
        throw error.toException(); // don't ignore errors
    }
});