Drop Down MenusCSS Drop Down MenuPure CSS Dropdown Menu

Friday, July 12, 2019

How to build 64-bit Xamarin Android Application

Google announced all Android app should support 64-bit architectures from Aug 1, 2019. 64-bit CPUs deliver faster, richer experiences for your users. Google Play will continue to support 32-bit apps for now, but as of August 1, 2019 all new apps and updates that include native code must have 64-bit versions as well as 32-bit versions when publishing to Google Play. This ruling applies to apps written in native, Xamarin or apps with links to third-party native libraries.

Android application supports four ABIs that can be selected when building mobile app. You can Select which ABIs your application supports in the project android options properties, if no ABI is specified, “armeabi-v71” is used in release build and As of Xamarin.Android 9.2, armeabi is no longer supported.

  1. armeabi-v7a – ARM-based CPUs with hardware floating-point operations and multiple CPU (SMP) devices.
  2. arm64-v8a – CPUs based on the 64-bit ARMv8 architecture.
  3. x86 – CPUs that support the x86 (or IA-32) instruction set.
  4. x86_64 – CPUs that support the 64-bit x86 .
You can follow the below steps for select 64-bit android application in the Visual studio and Visual studio mac.
Visual Studio in Windows machine:
Step 1: You can open Visual Studio in the windows machine, right-click on android project and select Properties
Step 2: Select the Android Options tab and Click the Advanced button and, check the architectures that you want to support.
Visual Studio Mac:
You can open Visual Studio mac in the mac machine and open/ create new project Android project.
Step 1:  Right-click on Android project under the Solution Explorer and select Properties.
Step 2: Under the Android Options page check the Packaging properties section and Click the Advanced button and select the architectures that you want to support:
How to check if your device is 32-bit or 64-bit?
You can also check if your phone is 64-bit in android using the app Antutu Benchmark. While this is a benchmarking app, you can just use it to view your device information. Open Antutu Benchmark and click on “info”.
The android applications already support 64-bit, no need to do anything, If you haven’t yet, you can change the as per the above steps as soon as possible. I hope this article will help you. Please leave your feedback/query using the comments box, and if you like this article, please share it with your friends.

Tuesday, July 2, 2019

Xamarin Forms: How to Read SMS and verify OTP automatically in android without using SMS read permission

Google is considering the users privacy seriously, it has updated its Google Play Developer Policy which restricting SMS, CALL_LOG access. If your app does not require access to Call Log or SMS permissions, you must remove the permissions from your app's manifest.
For apps requesting access to the SMS or Call Log permissions, the intended and permitted uses include default SMS handling, default phone handling, or Assistant handling capability, you should only access Call Log or SMS permissions when your app falls within permitted uses and only to enable your app’s critical core functionality.
Android App Should read the SMS some specific needs like verify OTP, The Google Play Services has enabled Android SMS Retriever API allows you to access the SMS Messages and verify it via SMS without device permissions. 
Verification Message Format:
You need to follow as per Google Policy for construct the verification message and send to the user device, the message should be following format.
  • Be no longer than 140 bytes
  • Begin with the prefix <#>
  • One-time Verification code
  • Special 11-character hash for you app. That Hash can be generated by the Application. (will explain following steps)
Now we have very good understanding about Google new policy and message format. This article, I will explain the following steps, it will help you to integrate Android OTP verification code auto read using Xamarin Forms.
  • Create New Xamarin Forms Application.
  • Add Google Play Services Auth
  • Create UI Design 
  • Dependency Service
  • Messaging Center subscribe 
  • ListenToSms Dependency
  • Broadcast Receiver
  • Generate Application Hash Key Helper
  • Demo Application
Create New Xamarin Forms Application
In order to implement Auto read OTP message, let’s start creating a new Xamarin.Forms project using Visual Studio 2019 or VS mac. When accessing Visual Studio 2019 mac for the first time, you will come across a new interface for opening a creating the projects.

Open Visual Studio Mac >>Create New Project or select open recent application.

The available templates will appear on a mac like below. Select Xamarin.Forms application with different mobile platforms.

Add Google Play Service NuGet Package:
After click on Next Button, The Xamairn Project template will generate and load the solutions into the local system. We need to install Xamarin.GooglePlayServices.Auth nuget package to our Android project for SMS Retriever API.
 Right click on Android Project >> Add Nuget Package >> Select or Search “Xamarin.GooglePlayServices.Auth”>> Install the Latest version of Google play service.

Create UI Design:
Create simple UI Design with one Entry and Button Control using Xaml in Xamarin Forms library.
<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="" xmlns:x="" xmlns:local="clr-namespace:ReadOTPXamarinAndroid" x:Class="ReadOTPXamarinAndroid.MainPage">
   <StackLayout Padding="15" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand" BackgroundColor="White">
        <Entry  PlaceholderColor="Black" Placeholder="Enter OTP" x:Name="smSEntry"></Entry>
        <Button Text="Wait for sms"  Clicked="ImageButton_OnClicked"></Button>

The Design Look like below 
Dependency Service
DependencyService allows apps to call into platform-specific functionality from shared code. This functionality enables Xamarin.Forms apps to do anything that a native app can do. We need to create a interface design will define how you interact with platform-specific functionality. Here, reading OTP will support only android Platform and IOS will support with Autofill so create DependencyService interface for Listen to sms retriever. Create new class and interface for CommonServices.
using Xamarin.Forms;

namespace ReadOTPXamarinAndroid
    public static class CommonServices
        public static void ListenToSmsRetriever()
    public interface IListenToSmsRetriever
        void ListenToSmsRetriever();


Messaging Center subscribe:
Xamarin.Forms MessagingCenter enables different components to communicate without having to know anything about each other besides a simple Message contract. The MessagingCenter is a static class with Subscribe and Send methods that are used throughout the solution.
Subscribe - Listen for messages with a certain signature and perform some action when they are received. Multiple subscribers can be listening for the same message.
Send - Publish a message for listeners to act upon. If no listeners have subscribed then the message is ignored.
Here, we are creating utility for subscribe message listener, it will help for if any new message recived the device notify to the solutions.
using System;
using System.Collections.Generic;
using System.Text;
using Xamarin.Forms;

namespace ReadOTPXamarinAndroid
   public static class Utilities
        private static readonly object cc = new object();
        public static void Subscribe<TArgs>(this object subscriber, Events eventSubscribed, Action<TArgs> callBack)
            MessagingCenter.Subscribe(subscriber, eventSubscribed.ToString(), new Action<object, TArgs>((e, a) => { callBack(a); }));
        public static void Notify<TArgs>(Events eventNotified, TArgs argument)
            MessagingCenter.Send(cc, eventNotified.ToString(), argument);

Create Enum for message Event type 
using System;
namespace ReadOTPXamarinAndroid
    public enum Events
Code Behind Design View:
The Code Behind add the Subscribe message listener and if any message receive from message app with specific format, it will get notify and read the meesage and assign the OTP value into the Entry Box.   
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
namespace ReadOTPXamarinAndroid
    public partial class MainPage : ContentPage
        public MainPage()
            this.Subscribe<string>(Events.SmsRecieved, code =>
                smSEntry.Text = code;
        private void ImageButton_OnClicked(object sender, EventArgs e)
ListenToSms Dependency:
Let start create dependency to android project ,if you are not added Xamarin.GooglePlayServices.Auth NuGet package, try to add before going to create Instance.
Get an instance of SmsRetrieverClient, used to start listening for a matching SMS message. 

SmsRetrieverClient client = SmsRetriever.GetClient(Application.Context);

Starts SmsRetriever, which waits for ONE matching SMS message until timeout (5 minutes). The matching SMS message will be sent via a Broadcast Intent .
            var task = client.StartSmsRetriever();
Listen for success/failure of the start Task. 
using Java.Lang;
using ReadOTPXamarinAndroid.Droid;
using Application = Android.App.Application;

[assembly: Dependency(typeof(ListenToSms))]

namespace ReadOTPXamarinAndroid.Droid
    public class ListenToSms : IListenToSmsRetriever
        public void ListenToSmsRetriever()
            SmsRetrieverClient client = SmsRetriever.GetClient(Application.Context);
            var task = client.StartSmsRetriever();
            task.AddOnSuccessListener(new SuccessListener());
            task.AddOnFailureListener(new FailureListener());
        private class SuccessListener : Object, IOnSuccessListener
            public void OnSuccess(Object result)
        private class FailureListener : Object, IOnFailureListener
            public void OnFailure(Exception e)

Broadcast Receiver:
The BroadcastReceiver that will be listening to the broadcasts of the above SmsRetreieverClient.SMS Retriever API has provided us with an intent filter SmsRetriever.SmsRetrievedAction which we will use to register our BroadcastReceiver, which we’re going name as SMSBroadcastReceiver, and implement as following.
using System.Linq;
using System.Text.RegularExpressions;
using Android.App;
using Android.Content;
using Android.Gms.Common.Apis;
using Com.Google.Android.Gms.Auth.Api.Phone;
using ReadOTPXamarinAndroid;

namespace ReadOTPXamarinAndroid.Droid
    [BroadcastReceiver(Enabled = true, Exported = true)]
    [IntentFilter(new[] { SmsRetriever.SmsRetrievedAction })]
    public class SmsReceiver : BroadcastReceiver
        private static readonly string[] OtpMessageBodyKeywordSet = { "DevEnvExe Generated OTP" }; //You must define your own Keywords
        public override void OnReceive(Context context, Intent intent)

                if (intent.Action != SmsRetriever.SmsRetrievedAction) return;
                var bundle = intent.Extras;
                if (bundle == null) return;
                var status = (Statuses)bundle.Get(SmsRetriever.ExtraStatus);
                switch (status.StatusCode)
                    case CommonStatusCodes.Success:
                        var message = (string)bundle.Get(SmsRetriever.ExtraSmsMessage);
                        var foundKeyword = OtpMessageBodyKeywordSet.Any(k => message.Contains(k));
                        if (!foundKeyword) return;
                        var code = ExtractNumber(message);
                        Utilities.Notify(Events.SmsRecieved, code);
                    case CommonStatusCodes.Timeout:

            catch (System.Exception)
                // ignored
        private static string ExtractNumber(string text)
            if (string.IsNullOrEmpty(text)) return "";
            var number = Regex.Match(text, @"\d+").Value;
            return number;

We have done code for now; it will go for testing. Before going to demo let we re consider the format of SMS, in that we need to get know about Application Hash key, Ley you follow below step for generate application hash key  
Generate Application Hash Key Helper
The hash string is made of your app’s package name and your app’s public key certificate. To generate the hash code, just run the following C# Method to generate hash to be included in your SMS message.
You need to make sure you are generate hash key and append to the OTP message, Without the correct hash, your app won't receive the message callback. 
Hash key will generate once per app and stored. Then you can remove this helper class from your code and create new class into the native android project.

using System;
using System.Linq;
using System.Text;
using Android.Content;
using Android.Content.PM;
using Android.Util;
using Java.Security;
using Java.Util;

namespace ReadOTPXamarinAndroid.Droid.Helper
    public class AppHashKeyHelper
        private static string HASH_TYPE = "SHA-256";
        private static int NUM_HASHED_BYTES = 9;
        private static int NUM_BASE64_CHAR = 11;

        /// <summary>
        /// Retrieve the app signed package signature
        /// known as signed keystore file hex string
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        private static string GetPackageSignature(Context context)
            PackageManager packageManager = context.PackageManager;
            var signatures = packageManager.GetPackageInfo(context.PackageName, PackageInfoFlags.Signatures).Signatures;
            return signatures.First().ToCharsString();

        /// <summary>
        /// Gets the app hash key.
        /// </summary>
        /// <returns>The app hash key.</returns>
        /// <param name="context">Android app Context.</param>
        public static string GetAppHashKey(Context context)
            string keystoreHexSignature = GetPackageSignature(context);

            String appInfo = context.PackageName + " " + keystoreHexSignature;
                MessageDigest messageDigest = MessageDigest.GetInstance(HASH_TYPE);
                byte[] hashSignature = messageDigest.Digest();

                hashSignature = Arrays.CopyOfRange(hashSignature, 0, NUM_HASHED_BYTES);
                String base64Hash = Android.Util.Base64.EncodeToString(hashSignature, Base64Flags.NoPadding | Base64Flags.NoWrap);
                base64Hash = base64Hash.Substring(0, NUM_BASE64_CHAR);

                return base64Hash;
            catch (NoSuchAlgorithmException e)
                return null;
You can call the GetAppHashkey method into MainActivity and debug the solution and get the hash key value.
Demo and Download Source Code:
The Application Ready now and you can also download the source code from Github , start the application using Android Emulator and click Phone icon from extended controls and add the message as per follow format with hash key. 

In this article, you learned about Verify OTP Automatically in Android without SMS read permission using Xamarin Forms. I hope this article will help you. Please leave your feedback/query using the comments box, and if you like this article, please share it with your friends.