How can I refresh recylverview item when i press back?

Question

I want to create a app like to do list. So created a DatabaseHelper Class. It contains DataAdd and DisplayDatafunction . There is recyclerView object in MainActivity for view all stored data. My functions are working but when I saved new data and I pressed back button , its saving but doesn't display on recyclerView . When I saved new data again its displaying. I think I can refresh recylerview when I pressed back in onBackPressed. How can I do it ?

...

package com.tcoding.hangidersdenkacsorucozdum;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

import com.google.android.material.floatingactionbutton.FloatingActionButton;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
    private RecyclerView rv ;
    private FloatingActionButton addButton ;
    DatabaseHelper db ;
    ArrayList<String> lessonId , lessonName , lessonSubject , solvedProblemCount ;
    CustomAdapter adapter ;

    private void init() {
        rv = (RecyclerView) findViewById(R.id.rv);
        addButton = (FloatingActionButton) findViewById(R.id.addButton);
        db = new DatabaseHelper(this);
        lessonId = new ArrayList<>();
        lessonName = new ArrayList<>();
        lessonSubject = new ArrayList<>();
        solvedProblemCount = new ArrayList<>();
        rv = findViewById(R.id.rv);
        adapter = new CustomAdapter(this , lessonId , lessonName , lessonSubject , solvedProblemCount);
        rv.setLayoutManager(new LinearLayoutManager(this));
        rv.setEnabled(true);
        rv.setAdapter(adapter);
    }

    @Override
    public void onBackPressed() {

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();

        addButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this,AddActivity.class));
            }
        });

        DisplayData();
    }

    void DisplayData(){

        Cursor c = db.showData();
        if(c.getCount() == 0){
            Toast.makeText(this, "Gösterilecek Veri Bulunamadı...", Toast.LENGTH_SHORT).show();
        } else {
            while(c.moveToNext()) {
                lessonId.add(c.getString(0));
                lessonName.add(c.getString(1));
                lessonSubject.add(c.getString(2));
                solvedProblemCount.add(c.getString(3));
            }
        }
    }
}

Answer 1

You need to grab data again inside onResume(), as onCreate() won't be called when you return back from AddActivity

So, to add the entire data you do something like

@Override
protected void onResume() {
    super.onResume();
    DisplayData();
    adapter.notifyDataSetChanged();
}

Or, from performance wise, it is better to notify of the last inserted item to the database.

@Override
protected void onResume() {
    super.onResume();
    Cursor c = db.showData();
    if(c.getCount() == 0){
        Toast.makeText(this, "Gösterilecek Veri Bulunamadı...", Toast.LENGTH_SHORT).show();
    } else {
        c.cursor.moveToLast()) 
        lessonId.add(c.getString(0));
        lessonName.add(c.getString(1));
        lessonSubject.add(c.getString(2));
        solvedProblemCount.add(c.getString(3));
    }
    adapter.notifyItemInserted(lessonId.getSize()-1);

}