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How to output sms on textview on sms Recieve?

I've made this simple app for recieving sms,When I receive a message I want to output this on my TextView,upuntil now for testing I was just doing
that inside a button .You recieve a message ,click on the button and you get the sms on textview.If I try to do this without a button ,at the start of compilation
I get a null reference exception.Can anyone help me on this ?
//----------MainActivity.cs---------------
using Android.App;
using Android.OS;
using Android.Support.V7.App;
using Android.Runtime;
using Android.Widget;
using Android.Content;
using Android.Telephony;
using Android.Provider;
using Android.Util;
using Java.Lang;
using System.Text.RegularExpressions;
using Xamarin.Essentials;
using System;
using Android;
using Android.Support.V4.Content;
using Android.Content.PM;
namespace Sms_Receiver2
{
[Activity(Label = "#string/app_name", Theme = "#style/AppTheme", MainLauncher = true)]
public class MainActivity : AppCompatActivity
{
public Receiver1 _receiver; // Receiver class
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.activity_main);
TextView translatedPhoneWord = FindViewById<TextView>(Resource.Id.TranslatedPhoneword);
Button translateButton = FindViewById<Button>(Resource.Id.TranslateButton);
if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.ReadSms) != (int)Permission.Granted)
{
RequestPermissions(new string[] { Manifest.Permission.ReadSms, Manifest.Permission.SendSms, Manifest.Permission.ReceiveSms }, 0);
}
translateButton.Click += (s, e) =>
{};
translatedPhoneWord.Text = _receiver.message;// null reference exception
}
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
{
Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}
protected override void OnResume()
{
base.OnResume();
_receiver = new Receiver1();
IntentFilter filter = new IntentFilter();
filter.AddAction("android.provider.Telephony.SMS_RECEIVED");
filter.AddAction("android.provider.Telephony.SMS_DELIVER");
RegisterReceiver(_receiver, filter);
}
protected override void OnPause()
{
base.OnPause();
UnregisterReceiver(_receiver);
}
}
}
//---------Reciever.cs -------------
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.Telephony;
using Android.Provider;
namespace Sms_Receiver2
{
[BroadcastReceiver(Enabled = true, Exported = true, Permission = "android.permission.BROADCAST_SMS")]
[IntentFilter(new[] { "android.provider.Telephony.SMS_RECEIVED", "android.provider.Telephony.SMS_DELIVER" }, Priority = (int)IntentFilterPriority.HighPriority)]
public class Receiver1 : BroadcastReceiver
{
public string message, address = "";
public static readonly string INTENT_ACTION = "android.provider.Telephony.SMS_RECEIVED";
public override void OnReceive(Context context, Intent intent)
{
if (intent.HasExtra("pdus"))
{
var smsArray = (Java.Lang.Object[])intent.Extras.Get("pdus");
foreach (var item in smsArray)
{
var sms = SmsMessage.CreateFromPdu((byte[])item);
address = sms.OriginatingAddress;
message = sms.MessageBody;
Toast.MakeText(context, "Number :" + address + "Message : " + message, ToastLength.Short).Show();
}
}
}
}
}

Slight modification of your code works
[Activity(Label = "#string/app_name", Theme = "#style/AppTheme.NoActionBar", MainLauncher = true)]
public class MainActivity : AppCompatActivity
{
private SMSBroadcastReceiver _receiver;
private TextView _smsTextView; //Textview where list of received sms will show
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.activity_main);
_smsTextView = FindViewById<TextView>(Resource.Id.smstextview);
_receiver = new SMSBroadcastReceiver();
_receiver.SmsActionDelegate = InokeOnNewSMS;
IntentFilter filter = new IntentFilter();
filter.AddAction("android.provider.Telephony.SMS_RECEIVED");
filter.AddAction("android.provider.Telephony.SMS_DELIVER");
RegisterReceiver(_receiver, filter);
}
//this method will be invoked when new sms is received in the broadcast received
public void InokeOnNewSMS(string address, string message)
{
_smsTextView.Text += $"{address} : {message}\n\n";
}
}
[BroadcastReceiver(Enabled = true, Exported = true, Permission = "android.permission.BROADCAST_SMS")]
[IntentFilter(new[] { "android.provider.Telephony.SMS_RECEIVED", "android.provider.Telephony.SMS_DELIVER" }, Priority = (int)IntentFilterPriority.HighPriority)]
public class SMSBroadcastReceiver : BroadcastReceiver
{
public string message = "", address = "";
public static readonly string INTENT_ACTION = "android.provider.Telephony.SMS_RECEIVED";
public Action<string, string> SmsActionDelegate;
public override void OnReceive(Context context, Intent intent)
{
if (intent.HasExtra("pdus"))
{
var smsArray = (Java.Lang.Object[])intent.Extras.Get("pdus");
foreach (var item in smsArray)
{
var sms = SmsMessage.CreateFromPdu((byte[])item);
address = sms.OriginatingAddress;
message = sms.MessageBody;
SmsActionDelegate?.Invoke(address, message);
Toast.MakeText(context, "Number :" + address + "Message : " + message, ToastLength.Short).Show();
}
}
}
}

foreground service never stop xamarin android

i have xamarin android application that read from clipboard and write to it. it uses foreground services if the user hit the button. the problem is when the user hit the button again the services disappear from running services but still doing it's job (editing copied text). how can i completely stop it from working?
foreground.cs:
public override IBinder OnBind(Intent intent)
{
return null;
}
public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
{
Clipboard.ClipboardContentChanged += async (o, e) =>
{
var text = await Clipboard.GetTextAsync();
Toast.MakeText(this, text, ToastLength.Long).Show();
if (text.Contains("#"))
{
await Clipboard.SetTextAsync(text.Replace("#", ""));
}
};
Notification notif = ReturnNotif();
StartForeground(1, notif);
return StartCommandResult.NotSticky;
}
public override void OnDestroy()
{
base.OnDestroy();
}
public override void OnCreate()
{
base.OnCreate();
}
public override bool StopService(Intent name)
{
StopForeground(true);
StopSelf();
return base.StopService(name);
}
MainActivity.cs:
if (id == Resource.Id.myService)
{
if (count != 1)
{
count = 1;
var intent = new Intent(this, typeof(foreground));
intent.SetAction("No");
if (Build.VERSION.SdkInt >= BuildVersionCodes.O)
{
StartForegroundService(intent);
}
else
{
StartService(intent);
}
}
else
{
var intent = new Intent(this,typeof(foreground));
StopService(intent);
Toast.MakeText(this, "Service Stopped", ToastLength.Long).Show();
count = 0;
}
}
what i am doing wrong ?
Edit :
Service will completely stops if the app is removed from recently used apps.

In your MyForegroundService.cs. Just add StopForeground(true) in OnDestroy() method like following code.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
namespace ForegroundServiceDemo
{
[Service]
class MyForegroundService : Service
{
public const int SERVICE_RUNNING_NOTIFICATION_ID = 10000;
[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
CreateNotificationChannel();
string messageBody = "service starting";
// / Create an Intent for the activity you want to start
Intent resultIntent = new Intent(this,typeof(Activity1));
// Create the TaskStackBuilder and add the intent, which inflates the back stack
TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);
stackBuilder.AddNextIntentWithParentStack(resultIntent);
// Get the PendingIntent containing the entire back stack
PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, PendingIntentFlags.UpdateCurrent);
var notification = new Notification.Builder(this, "10111")
.SetContentIntent(resultPendingIntent)
.SetContentTitle("Foreground")
.SetContentText(messageBody)
.SetSmallIcon(Resource.Drawable.main)
.SetOngoing(true)
.Build();
StartForeground(SERVICE_RUNNING_NOTIFICATION_ID, notification);
//do you work
return StartCommandResult.Sticky;
}
public override void OnDestroy()
{
base.OnDestroy();
StopForeground(true);
}
public override IBinder OnBind(Intent intent)
{
return null;
}
void CreateNotificationChannel()
{
if (Build.VERSION.SdkInt < BuildVersionCodes.O)
{
return;
}
var channelName = Resources.GetString(Resource.String.channel_name);
var channelDescription = GetString(Resource.String.channel_description);
var channel = new NotificationChannel("10111", channelName, NotificationImportance.Default)
{
Description = channelDescription
};
var notificationManager = (NotificationManager)GetSystemService(NotificationService);
notificationManager.CreateNotificationChannel(channel);
}
}
}
When you want to stop it. Just call following code.
Android.App.Application.Context.StopService(intent);
Here is my code in the Activity.
public class MainActivity : AppCompatActivity
{
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.activity_main);
Button button1 = FindViewById<Button>(Resource.Id.button1);
Button button2 = FindViewById<Button>(Resource.Id.button2);
button2.Click += Button2_Click;
button1.Click += Button1_Click;
}
Intent intent;
private void Button2_Click(object sender, System.EventArgs e)
{
// stop foreground service.
Android.App.Application.Context.StopService(intent);
}
private void Button1_Click(object sender, System.EventArgs e)
{
intent = new Intent(Android.App.Application.Context, typeof(MyForegroundService));
// start foreground service.
if (Android.OS.Build.VERSION.SdkInt >= Android.OS.BuildVersionCodes.O)
{
StartForegroundService(intent);
}
}
Here is running GIF.
====Update====
the expected behavior is : when service stopped user can copy and paste normally without the service interference
You can use following way to achieve that.Use Clipboard.ClipboardContentChanged += Clipboard_ClipboardContentChanged; to execute the behavior, use Clipboard.ClipboardContentChanged -= Clipboard_ClipboardContentChanged; to disable the behavior in the OnDistory method.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Xamarin.Essentials;
namespace ForegroundServiceDemo
{
[Service]
class MyForegroundService : Service
{
public const int SERVICE_RUNNING_NOTIFICATION_ID = 10000;
[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
CreateNotificationChannel();
string messageBody = "service starting";
Clipboard.ClipboardContentChanged += Clipboard_ClipboardContentChanged;
// / Create an Intent for the activity you want to start
Intent resultIntent = new Intent(this,typeof(Activity1));
// Create the TaskStackBuilder and add the intent, which inflates the back stack
TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);
stackBuilder.AddNextIntentWithParentStack(resultIntent);
// Get the PendingIntent containing the entire back stack
PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, PendingIntentFlags.UpdateCurrent);
var notification = new Notification.Builder(this, "10111")
.SetContentIntent(resultPendingIntent)
.SetContentTitle("Foreground")
.SetContentText(messageBody)
.SetSmallIcon(Resource.Drawable.main)
.SetOngoing(true)
.Build();
StartForeground(SERVICE_RUNNING_NOTIFICATION_ID, notification);
//do you work
return StartCommandResult.Sticky;
}
private async void Clipboard_ClipboardContentChanged(object sender, EventArgs e)
{
//throw new NotImplementedException();
var text = await Clipboard.GetTextAsync();
Toast.MakeText(this, text, ToastLength.Long).Show();
if (text.Contains("#"))
{
await Clipboard.SetTextAsync(text.Replace("#", ""));
}
}
public override void OnDestroy()
{
base.OnDestroy();
Clipboard.ClipboardContentChanged -= Clipboard_ClipboardContentChanged;
StopForeground(true);
}
public override IBinder OnBind(Intent intent)
{
return null;
}
void CreateNotificationChannel()
{
if (Build.VERSION.SdkInt < BuildVersionCodes.O)
{
return;
}
var channelName = Resources.GetString(Resource.String.channel_name);
var channelDescription = GetString(Resource.String.channel_description);
var channel = new NotificationChannel("10111", channelName, NotificationImportance.Default)
{
Description = channelDescription
};
var notificationManager = (NotificationManager)GetSystemService(NotificationService);
notificationManager.CreateNotificationChannel(channel);
}
}
}
Here is run GIF.

To prevent this issues, add a "myServiceIsRunning" bool value in the Properties dictionary when you start your foreground method like this:
Application.Current.Properties["myServiceIsRunning"] = true
With a get function or whatever you want, before start the foreground method, verify if the key "myServiceIsRunning" exist, and if it exist, how is his status:
public bool getRunningStateMyService(){
bool myServiceIsRunningValue;
if (Application.Current.Properties.ContainsKey("myServiceIsRunning"))
{
myServiceIsRunningValue = Convert.ToBoolean(Application.Current.Properties["myServiceIsRunning"]);
}
else
{
myServiceIsRunningValue = false;
}
return locationServiceIsRunning;
}
After you get the value, with a simple if{}/else{}, you can choose to start a new instance or not if you're service is running or not. Or, in you're case just prevent the foreground method continue to run.
Don't forget to set your value to false when you destroy the foreground method.
the Properties dictionary can store data trought closing app to. you can have more infos here:
https://learn.microsoft.com/fr-fr/xamarin/xamarin-forms/app-fundamentals/application-class#Properties_Dictionary

java.lang.IllegalArgumentException: No such service ComponentInfo{/com.SampleApp.AttendanceApp.ServiceClass}

I am using Xamarin Android to build an app which should allow the app to keep sending a driver's location every 15 minutes so that I can keep track of his movement. I used JobScheduler to get this done. My project is very simple now and only contains the following 3 files:
MainActivity.cs
AttendancePage.cs (Content page, interact with UI button to start the service)
ServiceClass.cs
Methods in Main Activity.cs
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
scheduler = (JobScheduler)GetSystemService(JobSchedulerService);
LoadApplication(new App()); //This line will then jump to AttendancePage.cs
}
public void ScheduleJob()
{
ComponentName componentName = new ComponentName(this, Java.Lang.Class.FromType(typeof(ServiceClass)));
JobInfo info = new JobInfo.Builder(123, componentName)
.SetPersisted(true)
.SetPeriodic(60000)
.Build();
int resultCode = scheduler.Schedule(info); //The error show when hit this line.
if (resultCode == JobScheduler.ResultSuccess)
{
Log.Info("Message", "Job Schedule!");
}
else
{
Log.Info("Message", "Job shceduling failed");
}
}
public void CancelJob()
{
scheduler.Cancel(123);
}
AttendancePage.cs
public partial class AttendancePage : ContentPage
{
MainActivity main = new MainActivity();
public AttendancePage()
{
InitializeComponent();
Title = "Attendance App";
}
//Button OnClickEvent
async void ScheduleJob(object s, EventArgs e)
{
main.ScheduleJob();
}
//Button OnClickEvent
async void CancelJob(object s, EventArgs e)
{
main.CancelJob();
}
}
ServiceClass.cs
[Service(Name = "com.SampleApp.AttendanceApp.ServiceClass", Permission = "android.permission.BIND_JOB_SERVICE")]
public class ServiceClass : JobService
{
public ServiceClass()
{
}
public override bool OnStartJob(JobParameters jobParamsOnStart)
{
doBackgroundWork(jobParamsOnStart);
return true;
}
private void doBackgroundWork(JobParameters jobParam)
{
//My code to send driver's location
TestingPage.GetGPS();
JobFinished(jobParam, false);
}
public override bool OnStopJob(JobParameters jobParamsOnStop)
{
return false;
}
}
I have added the service tag inside AndroidManifest.xml as well.
<service android:name=".ServiceClass"
android:permission="android.permission.BIND_JOB_SERVICE"
android:exported="true" />
I have no idea why the error is still there. The error is from the line scheduler.Schedule(JobInfo). Anyone has another possible solution? I am frustrated on solving this. Will the reason be I can't debug on the service but only can straight away run in release mode? Please help.

Froms shared code it works in Xamarin.Android project , however here is a Xamarin.Forms project . It can not work.
In AttendancePage.cs , you create a new MainActivity to invoke the native method ScheduleJob and CancelJob . This will not find the JobScheduler in native ,then it will return null .
No such service ComponentInfo{/com.SampleApp.AttendanceApp.ServiceClass}
If you want to invoke native method , you can have a try with DependencyService in Xamarin Forms .
At least need to create a Interface in Forms to invoke :
public interface IJobSchedulerService
{
//Start JobSchedule
void StartJobSchedule();
//Cancel JobSchedule
void CancelJobSchedule();
}
Then can invoke in Xamarin Forms as follow :
async void ScheduleJob(object s, EventArgs e)
{
DependencyService.Get<IJobSchedulerService>().StartJobSchedule();
}
//Button OnClickEvent
async void CancelJob(object s, EventArgs e)
{
DependencyService.Get<IJobSchedulerService>().CancelJobSchedule();
}
Now you need to implement the IJobSchedulerService in native android .Create the JobSchedulerDependcenyService:
public class JobSchedulerDependcenyService : IJobSchedulerService
{
JobScheduler jobScheduler;
public JobSchedulerDependcenyService()
{
jobScheduler = (JobScheduler)MainActivity.Instance.GetSystemService(Android.Content.Context.JobSchedulerService);
}
public void StartJobSchedule()
{
ComponentName componentName = new ComponentName(MainActivity.Instance, Java.Lang.Class.FromType(typeof(DownloadJob)));
JobInfo jobInfo = new JobInfo.Builder(1, componentName)
.SetOverrideDeadline(0)
.Build();
//var jobScheduler = (JobScheduler)GetSystemService(JobSchedulerService);
var scheduleResult = jobScheduler.Schedule(jobInfo);
if (JobScheduler.ResultSuccess == scheduleResult)
{
var snackBar = Snackbar.Make(MainActivity.Instance.FindViewById(Android.Resource.Id.Content), "jobscheduled_success", Snackbar.LengthShort);
snackBar.Show();
}
else
{
var snackBar = Snackbar.Make(MainActivity.Instance.FindViewById(Android.Resource.Id.Content), "jobscheduled_failure", Snackbar.LengthShort);
snackBar.Show();
}
}
public void CancelJobSchedule()
{
jobScheduler.CancelAll();
}
}
Here you will find the MainActivity.Instance inside it , that's a static instance defined by self in MainActivity.
public static MainActivity Instance { set; get; }
protected override void OnCreate(Bundle savedInstanceState)
{
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(savedInstanceState);
Instance = this;
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
LoadApplication(new App());
}

Xamarin Android Background Service crashes when the Application get closed

Hello, I want to build an app, in which you can start a service, which runs intependenly and creates a notification, and this service should constantly proof, if the DateTime.Now.Date is bigger than a spezific Date.
When I execute the code below, the notification gets displayed, but when I am closing the app, a few secondes later I get two times an information that the app crashed and I dont know why.
I cant even debug the code because this anly happens when the application is closed....
I hope you can help me thanks!
Here is my code:
namespace App
{
[Activity(Label = "App", MainLauncher = true, Icon = "#drawable/icon")]
public class MainActivity : Activity
{
int count = 1;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.Main);
// Get our button from the layout resource,
// and attach an event to it
Button button = FindViewById<Button>(Resource.Id.MyButton);
button.Click += delegate {
button.Text = string.Format("{0} clicks!", count++);
StartService(new Intent(this, typeof(backgroudservice)));
};
}
}
public class backgroudservice : Service
{
public override IBinder OnBind(Intent intent)
{
return null;
}
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
newnotification("Title", "Text: ", 0);
new Task(() => {
DoWork();
Thread.Sleep(1000);
}).Start();
return StartCommandResult.Sticky;
}
public void DoWork()
{
if (DateTime.Now.Date > Convert.ToDateTime("2016-03-29").Date)
{
cancelnotification(0);
StopSelf();
}
}
public override void OnDestroy()
{
base.OnDestroy();
cancelnotification(0);
}
private void newnotification(string titel, string text, int id)
{
Notification.Builder builder = new Notification.Builder(this)
.SetContentTitle(titel)
.SetContentText(text)
.SetSmallIcon(Resource.Drawable.droidlogo_small)
.SetAutoCancel(false)
.SetVisibility(NotificationVisibility.Public)
.SetContentIntent(PendingIntent.GetActivity(this, 0, new Intent(this, typeof(MainActivity)), PendingIntentFlags.OneShot));
// Build the notification:
Notification notification = builder.Build();
notification.Flags = NotificationFlags.NoClear;
//notification.ContentIntent = new Intent(this,typeof(login));
// Get the notification manager:
NotificationManager notificationManager = GetSystemService(Context.NotificationService) as NotificationManager;
// Publish the notification:
notificationManager.Notify(id, notification);
}
private void cancelnotification(int id)
{
NotificationManager notificationManager = GetSystemService(Context.NotificationService) as NotificationManager;
notificationManager.Cancel(id);
}
}
}

I solved it, I forgot the [Service] above my class, now it works!
[Service]
public class backgroudservice : Service
{
...
}

You might try moving the call to cancelnotification in your service's OnDestroy to before the call to the base method, i.e.:
public override void OnDestroy()
{
cancelnotification(0);
base.OnDestroy();
}

what wrong with my code?

My app always crashes when emulating the output shows unhandled exception.
I'm new to android and c#, so a little patience will be appreciated!!
namespace timer2
{
[Activity(Label = "timer2", MainLauncher = true, Icon = "#drawable/icon")]
public class MainActivity : Activity
{
static Button start, stop;
static TextView time;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
start = FindViewById<Button>(Resource.Id.start);
stop = FindViewById<Button>(Resource.Id.stop);
time = FindViewById<TextView>(Resource.Id.textView1);
SetContentView(Resource.Layout.Main);
time.Text = "00:03:00";
Counterclass timer = new Counterclass(180000, 1000);
start.Click += delegate
{
timer.Start();
};
stop.Click += delegate
{
timer.Cancel();
};
}
public class Counterclass : CountDownTimer
{
public Counterclass(long millisInFuture, long countDownInterval) :base(millisInFuture, countDownInterval)
{
}
public override void OnFinish()
{
time.Text = "Ready";
}
public override void OnTick(long millisUntilFinished)
{
long millis = millisUntilFinished;
string hms = String.Format("%02d:%02d:%02d", TimeSpan.FromMilliseconds(millis).Hours,
TimeSpan.FromMilliseconds(millis).Minutes - TimeSpan.FromHours(TimeSpan.FromMilliseconds(millis).Hours).Minutes,
TimeSpan.FromMilliseconds(millis).Seconds - TimeSpan.FromMinutes(TimeSpan.FromMilliseconds(millis).Minutes).Seconds);
time.Text = hms;
}
}
}
}

You need to set the content view before finding the controls:
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
SetContentView(Resource.Layout.Main);
start = FindViewById<Button>(Resource.Id.start);
stop = FindViewById<Button>(Resource.Id.stop);
time = FindViewById<TextView>(Resource.Id.textView1);