MainActivity.kt https://medium.com/@mohsenoid/how-to-setup-your-android-app-to-use-protobuf-96132340de5c

MainActivity.kt

// building PhoneNumber objects
val phoneHome = AddressBookProtos.Person.PhoneNumber.newBuilder()
        .setNumber("+49123456")
        .setType(AddressBookProtos.Person.PhoneType.HOME)
        .build()
val phoneMobile = AddressBookProtos.Person.PhoneNumber.newBuilder()
        .setNumber("+49654321")
        .setType(AddressBookProtos.Person.PhoneType.MOBILE)
        .build()

// building a Person object using phone data
val person = AddressBookProtos.Person.newBuilder()
        .setId(1)
        .setName("Mohsen")
        .setEmail("[email protected]")
        .addAllPhones(listOf(phoneHome, phoneMobile))
        .build()

// building an AddressBook object using person data
val addressBook = AddressBookProtos.AddressBook.newBuilder()
        .addAllPeople(listOf(person))
        .build()

// finally this is how you get serialized ByteArray
val bytes = addressBook.toByteArray()

// You can deserialize AddressBook bytes
val myAddressBook = AddressBookProtos.AddressBook.parseFrom(bytes)