get arrayList value into ArrayAdapter for a listView in android studio

Question

I am trying to put one piece of value in an ArrayList to my listView, below are the details.

Here is the sample of the ArrayList info:

private static final ArrayList<User> users = new ArrayList<User>(){{
        add(new User("Nevin Hobden",38,"Male","Friend","New Mexico","NM"));
        add(new User("Stillman Macken",32,"Male","Friend","Arizona","AZ"));
        add(new User("Stevy Ranscomb",36,"Male","Friend","Arizona","AZ"));
        add(new User("Lynelle Garstang",22,"Female","Family","California","NE"));

I want to grab the state data out from users ArrayList, eg. I only wish to get "New Mexico", "Arizona", "Arizona", and "California" data out to show it on my listView

if that is possible I also want to remove the duplicate and sort in ascending order

   Arizona
   California
   New Mexico

Below is the code I had

   ListView stateListView;
   ArrayList<DataServices.User> stateList = DataServices.getAllUsers();
   ArrayAdapter<DataServices> arrayListAdapter;

   stateListView = view.findViewById(R.id.stateListView);
   arrayListAdapter = new ArrayAdapter(getActivity(),android.R.layout.simple_list_item_1,android.R.id.text1, stateList);
   stateListView.setAdapter(arrayListAdapter);

I know I should not use stateList in the arrayAdapter however I have no idea how should I change for that part, any help is appreciated. Thanks!

Tyler V · Accepted Answer · 2022-06-11 16:08:35Z

2

If you want to get a list of the states, you can just loop over the original list and put the state into an ArrayList<String>, like this

ArrayList<String> states = new ArrayList<>();
for(DataServices.User user : users) {
    states.add(user.state);
}

If you only want unique states, you could just use a HashSet there instead. Sets eliminate duplicates.

HashSet<String> states = new HashSet<>();
for(User user : users) {
    states.add(user.state);
}

// then convert it back to a list
ArrayList<String> unique_states = new ArrayList<>(states);

And if you want it to be sorted, you can use Collections.sort to sort the list

Collections.sort(unique_states);

If your version of Java supports it, you can also do this in fewer lines with streams, but it accomplishes the same thing

List<String> statesList = users.stream()
                               .map(u -> u.state)
                               .collect(Collectors.toList());

Set<String> statesSet = users.stream()
                             .map(u -> u.state)
                             .collect(Collectors.toSet());

// Or in one-line
List<String> unique_states = users.stream()
                .map(u -> u.state)
                .collect(Collectors.toSet())
                .stream()
                .sorted()
                .collect(Collectors.toList());

edited Jun 11, 2022 at 16:08

answered Jun 11, 2022 at 15:34

Tyler V

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2 Comments

Michael Over a year ago

Since the users is in one class and the listview is in another fragment class, this solution seems need to do the function in the user class and call ArrayList in the fragment. Is there any way I do not need to change anything in the user? or do I have to?

Tyler V Over a year ago

If you have access to the list of users when you create the adapter, do this right before you make the adapter to make a list of states and just pass the list in to the adapter. You would just add it after you call List<User> users = DataServices.getAllUsers(); No changes to the User class or list are needed.

Ihor Bykov · Accepted Answer · 2022-06-11 15:43:15Z

0

Please don't use ListView. ListView is outdated and not so efficient as RecyclerView. Here is a good doc how to use RecyclerView

answered Jun 11, 2022 at 15:43

Ihor Bykov

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