How to sort an object from firebase?-CodePudding

Im getting an object from firebase, and there are two ways how i can get object

this one

text1
15.10.2021
text3
12.10.2021
text2
29.11.2021
text4
1.1.2022

or this one

{text = text1 , date = 15.10.2021}
{text = text3 , date = 12.10.2021}
{text = text2 , date = 29.11.2021}
{text = text4 , date = 1.1.2022}

I am need to sort this object by dates like that

text3 12.10.2021
text1 15.10.2021
text2 29.11.2021
text4 1.1.2022

I'm trying to add all into list but I don't know how to sort them. in list it looks like this

[text1, 15.10.2021, text3, 12.10.2021, text2, 29.11.2021, text4, 1.1.2022]

Im doing that for RecyclerView, and initially im getting dates and strings from Firebase like that


        List<String> reminder = new ArrayList<>();
        List<String> date = new ArrayList<>();



        dbf.child("Reminders").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

                reminder.clear();
                date.clear();


                for(DataSnapshot child2 : snapshot.getChildren()) { // getting a data from DB to ArrayList for dropping into Adapter

                    for(DataSnapshot tChild : child2.getChildren()) {


                        if (tChild.getKey().equals("text")) {
                            reminder.add(tChild.getValue().toString());
                            rem = reminder.toArray(new String[reminder.size()]); // rem = String[]


                        }
                        if (tChild.getKey().equals("date")) {
                            date.add(tChild.getValue().toString());
                            dat = date.toArray(new String[date.size()]); // dat = String[]


                        }

                    }



                    mainRowAdapter rAdapter = new mainRowAdapter(MainActivity.this, rem,dat);

                    rv.setAdapter(rAdapter);
                    rv.setLayoutManager(new LinearLayoutManager(MainActivity.this));

                }
            }

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

            }
        });

and then in Adapter class im use method setText()

so, the question in the top

CodePudding user response：

Your dates are stored as strings in a format that is unfortunately not chronologically sortable. If you want to sort on dates, I recommend storing them in ISO-8601 format, such as "2021-10-15" so that their lexicographical order matches their chronological order.

Once you have that format, you can retrieve the nodes from the database in the correct order with:

DatabaseReference reminders = dbf.child("Reminders");
Query remindersByDate = reminders.orderByChild("date");
remindersByDate.addValueEventListener(...

Also see: