Android Marshmallow Permissions Helper

PermissionsHelper.java

package dk.shape.goboat.managers;

import android.app.Activity;
import android.content.pm.PackageManager;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AlertDialog;

import java.util.ArrayList;
import java.util.List;

//
// Marshmallow Permissions Helper
//
// Created by Ben De La Haye on 02/03/2017.
//
// Usage:
// _permissionsHelper.requestPermission(this,
//      new PermissionsHelper.RequestData(Manifest.permission.WRITE_EXTERNAL_STORAGE,
//      getString(R.string.permission_explanation_external_storage),
//      () -> Toast.makeText(this, "Permission granted!", Toast.LENGTH_SHORT).show(),
//      () -> Toast.makeText(this, "Request permission failed!", Toast.LENGTH_SHORT).show()));
//
// Override the following in your Activity:
// @Override
// public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {
//     _permissionsHelper.onRequestPermissionsResult(requestCode, permissions, grantResults);
// }
//
public class PermissionsHelper {

    private static final int REQUEST_CODE = 1289;

    private List<RequestData> _ongoingPermissionData = new ArrayList<>();

    public void requestPermission(Activity activity, RequestData requestData) {

        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
            // No need to verify permissions
            requestData.onPermissionGranted();
            return;
        }

        _ongoingPermissionData.add(requestData);
        String permission = requestData.getPermission();

        if (ContextCompat.checkSelfPermission(activity, permission) != PackageManager.PERMISSION_GRANTED) {

            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(activity, permission)) {

                if (requestData.hasPermissionExplanation()) {

                    // Show an explanation to the user *asynchronously* -- don't block
                    // this thread waiting for the user's response! After the user
                    // sees the explanation, try again to request the permission.
                    new AlertDialog.Builder(activity)
                            .setMessage(requestData.getPermissionExplanation())
                            .setPositiveButton("Ok", (dialog, which) -> ActivityCompat.requestPermissions(activity, new String[]{permission}, REQUEST_CODE))
                            .setNegativeButton("Cancel", (dialog, which) -> dialog.dismiss())
                            .create().show();
                }

            } else {

                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(activity, new String[]{permission}, REQUEST_CODE);
            }
        }
    }

    public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {
        if (requestCode != REQUEST_CODE) return;

        for (RequestData requestData : _ongoingPermissionData) {

            for (int index = 0; index < permissions.length; index++) {

                if (permissions[0].contentEquals(requestData.getPermission())) {

                    // If request is cancelled, the result arrays are empty.
                    if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {

                        // permission was granted, yay! Do the
                        // contacts-related task you need to do.
                        requestData.onPermissionGranted();

                    } else {

                        // permission denied, boo! Disable the
                        // functionality that depends on this permission.
                        requestData.onPermissionFailed();
                    }

                    _ongoingPermissionData.remove(requestData);
                }
            }
        }
    }

    public static class RequestData {

        private String permission;
        private String permissionExplanation;

        private Runnable onPermissionGranted;
        private Runnable onPermissionFailed;

        public RequestData(String permission, String permissionExplanation, Runnable onPermissionGranted) {
            this.permission = permission;
            this.permissionExplanation = permissionExplanation;
            this.onPermissionGranted = onPermissionGranted;
        }

        public RequestData(String permission, String permissionExplanation, Runnable onPermissionGranted, Runnable onPermissionFailed) {
            this.permission = permission;
            this.permissionExplanation = permissionExplanation;
            this.onPermissionGranted = onPermissionGranted;
            this.onPermissionFailed = onPermissionFailed;
        }

        public String getPermission() {
            return permission;
        }

        public boolean hasPermissionExplanation() {
            return permissionExplanation != null;
        }

        public String getPermissionExplanation() {
            return permissionExplanation;
        }

        public void onPermissionGranted() {
            if (onPermissionGranted != null) onPermissionGranted.run();
        }

        public void onPermissionFailed() {
            if (onPermissionFailed != null) onPermissionFailed.run();
        }
    }
}