Pass Data Between Activities

// MainActivity.kt
binding.btnOpen.setOnClickListener {
    val intent = Intent(this, ProfileActivity::class.java).apply {
        putExtra("name", "Riya Sharma")
        putExtra("marks", 92)
        putExtra("isTopper", true)
    }
    startActivity(intent)
}

// ProfileActivity.kt
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding = ActivityProfileBinding.inflate(layoutInflater)
    setContentView(binding.root)

    val name = intent.getStringExtra("name") ?: "Unknown"     // String? → default
    val marks = intent.getIntExtra("marks", 0)               // default if missing
    val isTopper = intent.getBooleanExtra("isTopper", false)

    binding.tvName.text = name
    binding.tvMarks.text = "Marks: $marks"
    binding.tvBadge.isVisible = isTopper
}

class ProfileActivity : AppCompatActivity() {
    companion object {
        const val EXTRA_NAME = "extra_name"
        const val EXTRA_MARKS = "extra_marks"

        // a "factory" – callers cannot forget a key
        fun newIntent(context: Context, name: String, marks: Int) =
            Intent(context, ProfileActivity::class.java)
                .putExtra(EXTRA_NAME, name)
                .putExtra(EXTRA_MARKS, marks)
    }
}

// caller
startActivity(ProfileActivity.newIntent(this, "Riya Sharma", 92))

// app/build.gradle.kts
plugins {
    alias(libs.plugins.android.application)
    alias(libs.plugins.kotlin.android)
    id("kotlin-parcelize")                 // add this line
}

import android.os.Parcelable
import kotlinx.parcelize.Parcelize

@Parcelize
data class Student(val id: Int, val name: String, val marks: Int, val city: String) : Parcelable

// send
val student = Student(7, "Aman Verma", 88, "Aligarh")
startActivity(Intent(this, ProfileActivity::class.java).putExtra("student", student))

// receive (API 33+ has a type-safe version; IntentCompat works on all versions)
val s: Student? = IntentCompat.getParcelableExtra(intent, "student", Student::class.java)
binding.tvName.text = s?.name

// MainActivity – open the editor and wait for the new name
private val editName = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
    if (result.resultCode == RESULT_OK) {
        val newName = result.data?.getStringExtra("new_name")
        binding.tvName.text = newName
    }
}

binding.btnEdit.setOnClickListener {
    editName.launch(Intent(this, EditNameActivity::class.java).putExtra("old_name", binding.tvName.text.toString()))
}

// EditNameActivity – send the result back
binding.etName.setText(intent.getStringExtra("old_name"))
binding.btnSave.setOnClickListener {
    val data = Intent().putExtra("new_name", binding.etName.text.toString())
    setResult(RESULT_OK, data)
    finish()
}