Question

我想做的是按id排序数据。我知道我应该使用booksInstance.orderByChild（“id”）。我试过这样做，没有任何改变，因为我不知道我应该在代码中使用它。这是我如何显示数据。

private void getData(){
        firebaseDatabaseInstance = FirebaseDatabase.getInstance();
        // get reference to 'users' node
        booksInstance = firebaseDatabaseInstance.getReference("a3lamAlda3wa");
        books.clear();
        books.addAll(db.getAllA3());
        adapter = new BookGridAdapter(this, books);
        gridView.setAdapter(adapter);
        if (books.isEmpty()) {
            Constants.showLoadingDialog(this);
        }
        booksInstance.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                storeData(dataSnapshot);
            }
            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.w(TAG, "Failed to read value.", error.toException());
            }
        });
        booksInstance.orderByChild("id").addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                BookData book = new BookData(

                        (String) dataSnapshot.child("id").getValue(),
                        (String) dataSnapshot.child("book_name").getValue(),
                        (String)dataSnapshot.child("book_path").getValue(),
                        (String)dataSnapshot.child("book_path2").getValue(),
                        "",
                        (String)dataSnapshot.child("image_path").getValue(),
                        (String)dataSnapshot.child("image_path2").getValue(),
                        ""
                );
                db.insertA3(book);
                reloadData();
            }
        });
    }
       private void storeData(DataSnapshot snapshot) {
        books.clear();
        for (DataSnapshot alert: snapshot.getChildren()) {
            BookData book = new BookData(
                    (String)alert.child("id").getValue(),
                    (String)alert.child("book_name").getValue(),
                    (String)alert.child("book_path").getValue(),
                    (String)alert.child("book_path2").getValue(),
                    "",
                    (String)alert.child("image_path").getValue(),
                    (String)alert.child("image_path2").getValue(),
                    ""
            );
            db.insertBook(book);
        }
        books.addAll(db.getAllBook());
        adapter.notifyDataSetChanged();
    }

这就是我的数据库的样子

 "books" : [ null, {
        "book_name" : "book 1",
        "book_path" : "gs://appspot.com/books/1.pdf",
        "book_path2" : "https://firebasestorage.googleapis.com",
        "id" : "a-1",
        "image_path" : "gs://mostsharabdallah-c0c65.appspot.com",
        "image_path2" : "https://firebasestorage.googleapis.com"
      }

Answer 1

不是将侦听器附加到书籍的位置，而是将其附加到有序查询。所以：

booksInstance.orderByChild("id").addChildEventListener(new ChildEventListener() {

出于好奇：由于您的图书已经有ID，为什么不简单地将它们作为密钥存放在他们的ID下？

在firebase数据库android上按id排序

1 个答案: