Android: Show dialog without activity context

Dialog is built by ui context. The approach to show dialog without ui context (activity) in some case: call dialog in rest api, show dialog after own activity finish, call dialog in first activity and want to show it in the next activity also.

First: use Broadcast receiver

Assume: We call open dialog after delay timeout and run TestActivity concurrently in MainActivity.

import android.app.Activity;
import android.app.AlertDialog;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.IntentFilter;

import java.util.HashMap;

/**
 * Created by nhancao on 10/31/16.
 */

public class Alerts {
    public static void register(Activity activity) {
        AlertReceiver.register(activity);
    }

    public static void unregister(Activity activity) {
        AlertReceiver.unregister(activity);
    }

    public static void displayError(Context context, String msg) {
        Intent intent = new Intent("MyApplication.INTENT_DISPLAYERROR");
        intent.putExtra(Intent.EXTRA_TEXT, msg);
        context.sendOrderedBroadcast(intent, null);
    }

    private static void displayErrorInternal(Context context, String msg) {
        AlertDialog.Builder builder = new AlertDialog.Builder(context);
        builder.setTitle("Error").setMessage(msg).setCancelable(false).setPositiveButton("Ok", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();
            }
        });
        final AlertDialog alert = builder.create();
        alert.show();
    }

    private static class AlertReceiver extends BroadcastReceiver {
        private static HashMap<Activity, AlertReceiver> registrations;

        static {
            registrations = new HashMap<Activity, AlertReceiver>();
        }

        private Context activityContext;

        private AlertReceiver(Activity activity) {
            activityContext = activity;
        }

        static void register(Activity activity) {
            AlertReceiver receiver = new AlertReceiver(activity);
            activity.registerReceiver(receiver, new IntentFilter("MyApplication.INTENT_DISPLAYERROR"));
            registrations.put(activity, receiver);
        }

        static void unregister(Activity activity) {
            AlertReceiver receiver = registrations.get(activity);
            if (receiver != null) {…