Activity間

AndroidManifest.xmlに親子関係を記載

<activity android:name=".MainActivity"
          android:parentActivityName=".NextActivity">

送る側

MainActivity.kt

fun toNextView(view: View){
    val intent = Intent(this, Main2Activity::class.java)
    intent.putExtra("key", "sample")
    startActivity(intent)
}

受け取り側

NextActivity.kt

val text = intent.getStringExtra("key") // sample

Fragment間

送る側

FirstFragment.kt

val bundle = Bundle()
bundle.putString("key", "sample")
val fragment = SecondFragment()
fragment.arguments = bundle
parentFragmentManager.beginTransaction()
        .add(R.id.container, fragment)
        .commit()

受け取り側

SecondFragment.kt

val args = arguments?.getString("key") // sample