Base flow for handling Android permission request and response in Kotlin

00_Generic permission handler in Kotlin.md

To be placed in a main parent Activity, or as part of some custom BaseActivity class for handling permission request and responses without losing the "flow".

Example usage:

btn_load_timeline?.setOnClickListener {
    permissionCheck(Manifest.permission.READ_EXTERNAL_STORAGE, PermissionRequestCode.TIMELINE_FEATURE_EXTERNAL_STORAGE) { permissionResponse ->
        when (permissionResponse) {
            PermissionResponse.PERMISSION_GRANTED -> {
                Log.d(TAG, "Permission granted, load timeline here")
                // Do stuff with granted permission
            }
            PermissionResponse.PERMISSION_DENIED -> {
                Log.d(TAG, "Permission Denied, but can still prompt again")
                // Can prompt for permission again, or show rationale, etc.
            }
            PermissionResponse.PERMISSION_DONT_SHOW_AGAIN -> {
                Log.d(TAG, "Permission Denied, and user selected 'Don't Show Again'")
                // Disable feature, and/or let user know they'll need to go to Settings > App Info to enable the permission
            }
        }
    }
}

BaseActivity.kt

package com.justbnutz.labs

import android.content.pm.PackageManager
import android.view.View
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
import com.google.android.material.snackbar.Snackbar
import com.justbnutz.labs.models.PermissionRequestCode
import com.justbnutz.labs.models.PermissionResponse
import java.util.*

/**
 * Common methods between all activities go here
 */
abstract class BaseActivity : AppCompatActivity() {

    // A queue of actions to take after we get the permission response callback, indexed by the request code enum
    private val permissionResponseQueue: EnumMap<PermissionRequestCode, (PermissionResponse) -> Unit> by lazy { EnumMap(PermissionRequestCode::class.java) }

    fun permissionCheck(requestedPermission: String, requestCode: PermissionRequestCode, permissionResponse: (PermissionResponse) -> Unit) {
        if (checkSelfPermission(requestedPermission) == PackageManager.PERMISSION_GRANTED) {
            // We have permission, can immediately execute the response action
            permissionResponse(PermissionResponse.PERMISSION_GRANTED)
        } else {
            // Permission not (yet) granted, trigger a request and handle the rest of the flow in onRequestPermissionsResult()
            requestPermissions(arrayOf(requestedPermission), requestCode.ordinal)

            // Queue up the response action so we can pick it up again in onRequestPermissionsResult() callback
            permissionResponseQueue[requestCode] = permissionResponse
        }
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        // Check if requestCode matches an ordinal key value in permissionResponseQueue
        permissionResponseQueue.entries.firstOrNull { it.key.ordinal == requestCode }?.also { (key, permissionResponse) ->
            // Note: Can only handle singular permission requests for now: TODO: Handle multi-permission requests
            permissions.firstOrNull()?.let { requestedPermission ->
                grantResults.firstOrNull()?.let { permissionResult ->
                    when {
                        (permissionResult == PackageManager.PERMISSION_GRANTED) -> {
                            // Permission granted, do the action
                            permissionResponse(PermissionResponse.PERMISSION_GRANTED)
                        }
                        shouldShowRequestPermissionRationale(requestedPermission) -> {
                            // Permission previously denied, but "Don't Show Again" left unchecked; can prompt again
                            permissionResponse(PermissionResponse.PERMISSION_DENIED)
                        }
                        else -> {
                            // Permission previously denied and "Don't show again" was checked; need to provide link to App Info / Settings.
                            permissionResponse(PermissionResponse.PERMISSION_DONT_SHOW_AGAIN)
                        }
                    }
                }
            }
            // Response handled; remove the action item from the queue
            permissionResponseQueue.remove(key)
        } ?: run {
            // Request code is not part of the queue, let system handle response
            super.onRequestPermissionsResult(requestCode, permissions, grantResults)
        }
    }


    fun showSnackbar(view: View, message: String) {
        Snackbar.make(view, message, Snackbar.LENGTH_SHORT).show()
    }

    fun showToast(message: String) {
        Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
    }
}

PermissionRequestCode.kt

package com.justbnutz.labs.models

/**
 * Can use any name here - one entry for each permission journey.
 * Allows the onRequestPermissionsResult callback to know which
 * which journey to return to upon receiving the response.
 * 
 * Use PermissionRequestCodes.<permission_request_flow>.ordinal
 * to get the Int value and use these as callback request codes
 */
enum class PermissionRequestCode {
    TIMELINE_FEATURE_EXTERNAL_STORAGE,
    SHARE_FEATURE_READ_CONTACT,
    ANY_DESCRIPTIVE_NAME_BLAH_BLAH
}

PermissionResponse.kt

package com.justbnutz.labs.models

/**
 * Denotes the three possible paths that could come from a permission request.
 */
enum class PermissionResponse {
    PERMISSION_GRANTED,
    PERMISSION_DENIED,
    PERMISSION_DONT_SHOW_AGAIN
}