Android Functional Activity Approach

FunctionalActivityExample.kt

package com.methodsignature.kotlin.example
import android.app.Activity
import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.widget.Toast

/**
 * Base class that supports composition and handles the boilerplate.
 */
open class BaseActivity: AppCompatActivity() {
    private val activityResultHandlers = mutableMapOf<Int, (Int, Intent?) -> Unit>()
    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        activityResultHandlers[requestCode]?.apply {
            invoke(resultCode, data)
        }
    }
    fun addActivityResultHandler(requestCode: Int, action: (Int, Intent?) -> Unit) {
        activityResultHandlers[requestCode] = action
    }
}

/**
 * Worker Activity
 */
class SomeActivity: BaseActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val intent = Intent(this, SomeOtherActivity::class.java)
        addActivityResultHandler(REQUEST_DO_SOME_WORK, toastActivityResult)
        startActivityForResult(intent, REQUEST_DO_SOME_WORK)
    }
    private val toastActivityResult: (Int, Intent?) -> Unit = { resultCode, _ ->
        if (resultCode == Activity.RESULT_OK) {
            Toast.makeText(this, "Result was a success", Toast.LENGTH_SHORT).show()
        }
    }
    companion object {
        const val REQUEST_DO_SOME_WORK = 5738
    }
}

/**
 * Just here for reference.
 */
class SomeOtherActivity: AppCompatActivity()