Android Activityから別のActivityを呼ぶ

startActivityForResult()が、deprecated(非推奨)になりました
registerForActivityResult()を使用して記述する方法です

MainActivity.kt

package com.sample.subactivity

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.view.View.OnClickListener
import androidx.activity.result.contract.ActivityResultContracts
import com.a.subactivity.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity(), OnClickListener {
    private lateinit var binding: ActivityMainBinding

    // launcherは、クラスのフィールド変数として定義すること
    private val launcher =
        registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { res ->
            run {
                if (res.resultCode == RESULT_OK) {
                    val subText = res.data?.getStringExtra("sub")
                    binding.textView.text = subText
                }
            }
        }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)
    }

    override fun onClick(v: View?) {
        val intent = Intent(this, SubActivity::class.java)
        val mainText = binding.editText.text.toString()
        intent.putExtra("main", mainText)

        launcher.launch(intent)
    }
}

SubActivity.kt

package com.sample.subactivity

import android.content.Intent
import android.os.Bundle
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import com.a.subactivity.databinding.ActivityMainBinding

class SubActivity : AppCompatActivity(), View.OnClickListener {
    // このサンプルでは、SubActivityのレイアウトファイルは、MainActivityのactivity_main.xmlを共通で使用している
    private lateinit var binding: ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val extras = intent.extras
        val mainText = extras?.getString("main")
        binding.textView.text = mainText
    }

    override fun onClick(v: View?) {
        val intent = Intent()
        val subText = binding.editText.text.toString()
        intent.putExtra("sub", subText)
        setResult(RESULT_OK, intent)
        finish()
    }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/text_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Button" />

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="text" />
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.SubActivity"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <!--SubActivityを定義する-->
        <activity android:name="com.sample.subactivity.SubActivity" />
    </application>

</manifest>

build.gradle (Module :app)

plugins {
    id 'com.android.application'
    id 'org.jetbrains.kotlin.android'
}

android {
    namespace 'com.a.subactivity'
    compileSdk 33

    defaultConfig {
        applicationId "com.sample.subactivity"
        minSdk 23
        targetSdk 33
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }

    // view bindingを使用するため定義する
    viewBinding {
        enabled = true
    }
}

dependencies {

    implementation 'androidx.core:core-ktx:1.8.0'
    implementation 'androidx.appcompat:appcompat:1.6.1'
    implementation 'com.google.android.material:material:1.5.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.4'
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test.ext:junit:1.1.5'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.5.1'
}