使用Retrofit将数据添加到数据库时，如何刷新RecyclerView？

Question

I'm making some tests using Retrofit2 to show a list of users and to create a new user. My problem is how to refresh a RecyclerView after adding a user with a POST request to my api.

I have a MainActivity that make the GET request to a Laravel api. Then, I make a CreateUserActivity that has the form for create a new user. After I click on Create User button, I finish that activity to show the MainActivity , but I want to update the RecyclerView with the new user.

CreateUserActivity.java

public class CreateUserActivity extends AppCompatActivity {

    private TextInputEditText inputFirstName;
    private TextInputEditText inputLastName;
    private TextInputEditText inputEmail;
    private TextInputEditText inputPassword;
    private Button saveButton;
    private ApiService api;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_create_user);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        inputFirstName = (TextInputEditText) findViewById(R.id.txtInputFirstName);
        inputLastName = (TextInputEditText) findViewById(R.id.txtInputLastName);
        inputEmail = (TextInputEditText) findViewById(R.id.txtInputEmail);
        inputPassword = (TextInputEditText) findViewById(R.id.txtInputPassword);
        saveButton = (Button) findViewById(R.id.btnCreateUser);

        api = RetroClient.getApiService();

        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String firstName = inputFirstName.getText().toString().trim();
                String lastName = inputLastName.getText().toString().trim();
                String email = inputEmail.getText().toString().trim();
                String password = inputPassword.getText().toString().trim();

                User user = new User();

                user.setFirstName(firstName);
                user.setLastName(lastName);
                user.setEmail(email);
                user.setPassword(password);
                user.setGenreId(1);

                if (!TextUtils.isEmpty(firstName)) {
                    sendPost(user);
                }
            }
        });
    }

    private void sendPost(User user) {
        Call<User> call = api.saveUser(user);

        call.enqueue(new Callback<User>() {
            @Override
            public void onResponse(Call<User> call, Response<User> response) {

                if(response.isSuccessful()) {
                    String message = "Usuario creado correctamente";
                    Toast.makeText(getApplicationContext(), message, Toast.LENGTH_SHORT).show();
                    setResult(RESULT_OK);
                    finish();
                }

            }

            @Override
            public void onFailure(Call<User> call, Throwable t) {
                System.out.println("Fail");
            }
        });
    }

MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getApplicationContext(), CreateUserActivity.class);
                startActivityForResult(intent, 1);
            }
        });

        ApiService api = RetroClient.getApiService();

        Call<UsersList> call = api.getUsers();

        call.enqueue(new Callback<UsersList>() {
            @Override
            public void onResponse(Call<UsersList> call, Response<UsersList> response) {
                if (!response.isSuccessful()) {
                    return;
                }

                usersList = response.body().getUser();
                usersRecyclerView = (RecyclerView) findViewById(R.id.dataTable);
                usersAdapter = new UsersAdapter(usersList);
                RecyclerView.LayoutManager usersLayoutManager = new LinearLayoutManager(getApplicationContext());
                usersRecyclerView.setLayoutManager(usersLayoutManager);
                usersRecyclerView.setItemAnimator(new DefaultItemAnimator());
                usersRecyclerView.setAdapter(usersAdapter);

            }

            @Override
            public void onFailure(Call<UsersList> call, Throwable t) {
            }
        });

    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == 1 && resultCode == RESULT_OK) {
            usersAdapter.notifyDataSetChanged();
        }

    }

Answer 1

So create a setUserList function in your UserAdapter class and inside it use notifyDatabaseChange() after setting the userlist inside adapter to the new list.

 public void setUserList(List<UserList> userList) {
    userList.clear();
    this.userList  = userList;
    notifyDataSetChanged();

}