from first activity to second and back android example

different files.java

MainActivity.java:

package site.sunmeat.helloworld;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.widget.*;
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {
    String TAG = "first_activity";
    int value = 10;

    // це треба зробити полем, інакше виліт
    ActivityResultLauncher<Intent> l = registerForActivityResult(
            new ActivityResultContracts.StartActivityForResult(),
            result -> {
                if (result.getResultCode() == Activity.RESULT_OK) {
                    Intent r = result.getData();
                    if (r != null) {
                        int data = r.getIntExtra("result", 0);
                        Toast.makeText(this, data + "", Toast.LENGTH_SHORT).show();
                    }
                }
            });

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

        Log.i(TAG, "FIRST ACTIVITY: onCreate");
        Button b = findViewById(R.id.but1);
        b.setOnClickListener(v -> {
            var i = new Intent(this, SecondActivity.class);
            i.putExtra("data", value);
            Log.i(TAG, this + "");
            l.launch(i);
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "FIRST ACTIVITY: onDestroy");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "FIRST ACTIVITY: onRestart");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "FIRST ACTIVITY: onStart");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "FIRST ACTIVITY: onStop");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "FIRST ACTIVITY: onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "FIRST ACTIVITY: onPause");
    }
}

=============================================================================================================
  
activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#121926">

    <Button
        android:id="@+id/but1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="4dp"
        android:text="FIRST ACTIVITY" />
</RelativeLayout>

=============================================================================================================

SecondActivity.java:

package site.sunmeat.helloworld;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.widget.*;
import androidx.appcompat.app.AppCompatActivity;

public class SecondActivity extends AppCompatActivity {
    String TAG = "second_activity";

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

        Log.i(TAG, this + "");

        int value = 0;
        Intent parent = getIntent(); // отримуємо батьківський намір на створення актівіті (якщо він звісно існує)
        if (parent != null) {
            value = parent.getIntExtra("data", 0);
            Toast.makeText(this, value + "", Toast.LENGTH_SHORT).show();
        }

        Log.i(TAG, "SECOND ACTIVITY: onCreate");

        Button b = findViewById(R.id.but2);
        b.setOnClickListener(v -> {
            var intent = new Intent();
            intent.putExtra("result", 221);
            setResult(Activity.RESULT_OK, intent);
            finish();
        });

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "SECOND ACTIVITY: onDestroy");
    }

    @Override
    protected void onRestart() {
        super.onRestart();
        Log.i(TAG, "SECOND ACTIVITY: onRestart");
    }

    @Override
    protected void onStart() {
        super.onStart();
        Log.i(TAG, "SECOND ACTIVITY: onStart");
    }

    @Override
    protected void onStop() {
        super.onStop();
        Log.i(TAG, "SECOND ACTIVITY: onStop");
    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.i(TAG, "SECOND ACTIVITY: onResume");
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.i(TAG, "SECOND ACTIVITY: onPause");
    }
}

=============================================================================================================
  
activity_second.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#121926">

    <Button
        android:id="@+id/but2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="4dp"
        android:text="SECOND ACTIVITY" />
</RelativeLayout>