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Xamarin C# activity on screen (un)lock event

Just wondering if there is an event In Xamarin for the activity class like OnStart, OnResume, OnPause etc. that gets fired when the user locks or unlocks their screen while the app is open, I've been looking for such an event in documentation etc, but I haven't been able to find it.
If there is no such event, then how can we create it?

Xamarin C# activity on screen (un)lock event
you could create a listener class to listen for android lock screen and unlock events，use broadcast to receive the state of screen.
first create a ScreenListener.cs :
public class ScreenListener
{
private Context mContext;
private ScreenBroadcastReceiver mScreenReceiver;
private static ScreenStateListener mScreenStateListener;
public ScreenListener(Context context)
{
mContext = context;
mScreenReceiver = new ScreenBroadcastReceiver();
}
/**
* screen BroadcastReceiver
*/
private class ScreenBroadcastReceiver : BroadcastReceiver
{
private String action = null;
public override void OnReceive(Context context, Intent intent)
{
action = intent.Action;
if (Intent.ActionScreenOn == action)
{ // screen on
mScreenStateListener.onScreenOn();
}
else if (Intent.ActionScreenOff == action)
{ // screen off
mScreenStateListener.onScreenOff();
}
else if (Intent.ActionUserPresent == action)
{ // unlock
mScreenStateListener.onUserPresent();
}
}
}
/**
* begin to listen screen state
*
* #param listener
*/
public void begin(ScreenStateListener listener)
{
mScreenStateListener = listener;
registerListener();
getScreenState();
}
/**
* get screen state
*/
private void getScreenState()
{
PowerManager manager = (PowerManager)mContext
.GetSystemService(Context.PowerService);
if (manager.IsScreenOn)
{
if (mScreenStateListener != null)
{
mScreenStateListener.onScreenOn();
}
}
else
{
if (mScreenStateListener != null)
{
mScreenStateListener.onScreenOff();
}
}
}
/**
* stop listen screen state
*/
public void unregisterListener()
{
mContext.UnregisterReceiver(mScreenReceiver);
}
/**
* regist screen state broadcast
*/
private void registerListener()
{
IntentFilter filter = new IntentFilter();
filter.AddAction(Intent.ActionScreenOn);
filter.AddAction(Intent.ActionScreenOff);
filter.AddAction(Intent.ActionUserPresent);
mContext.RegisterReceiver(mScreenReceiver, filter);
}
public interface ScreenStateListener
{// Returns screen status information to the caller
void onScreenOn();
void onScreenOff();
void onUserPresent();
}
}
then in the MainActivity.cs:
public class MainActivity : AppCompatActivity,ScreenStateListener
{
ScreenListener mScreenListener;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
SetContentView(Resource.Layout.activity_main);
mScreenListener = new ScreenListener(this);
}
protected override void OnDestroy()
{
base.OnDestroy();
mScreenListener.unregisterListener();
}
protected override void OnResume()
{
base.OnResume();
mScreenListener.begin(this);
}
public void onScreenOn()
{
Console.WriteLine("onScreenOn");
}
public void onScreenOff()
{
Console.WriteLine("onScreenOff");
}
public void onUserPresent()
{
Console.WriteLine("onUserPresent");
}
}

Here's a sample of Xamarin.Android activities lifecycle.
You can override any of the lifecycle methods like this:
protected override void OnResume() {
base.OnResume();
}
Like in native Android OnPause is fired when the system is about to put the activity into the background. OnResume is called when the activity is ready to start interacting with the user.
OnPause and OnResume can be used for your (un)lock events.

Showing Google Admob Interstitial ad in Xamarin Forms without delay

I'm working on Xamarin forms project and i have implemented Interstitial ad on all three platforms (Google admob doesn't support UWP). Ads are working fine but they are showing with a delay of 4 to 5 seconds. All i want is to finish that delay so they can show immediately.
PCL class.
public interface IAdmobInterstitial
{
void Show(string adUnit);
}
Droid Code.
public class InterstitialAdListener : AdListener
{
readonly InterstitialAd _ad;
public InterstitialAdListener(InterstitialAd ad)
{
_ad = ad;
}
public override void OnAdLoaded()
{
base.OnAdLoaded();
if (_ad.IsLoaded)
_ad.Show();
}
}
public class AdmobInterstitial : Controls.IAdmobInterstitial
{
InterstitialAd _ad;
public void Show(string adUnit)
{
var context = Android.App.Application.Context;
_ad = new InterstitialAd(context);
_ad.AdUnitId = adUnit;
var intlistener = new InterstitialAdListener(_ad);
intlistener.OnAdLoaded();
_ad.AdListener = intlistener;
var requestbuilder = new AdRequest.Builder().AddTestDevice("302E90D530B2193F59FDD7F22A11B45A");
_ad.LoadAd(requestbuilder.Build());
}
}
iOS Code.
public class AdmobInterstitial : IAdmobInterstitial
{
Interstitial _adInterstitial;
public void Show(string adUnit)
{
_adInterstitial = new Interstitial(adUnit);
var request = Request.GetDefaultRequest();
_adInterstitial.AdReceived += (sender, args) =>
{
if (_adInterstitial.IsReady)
{
var window = UIApplication.SharedApplication.KeyWindow;
var vc = window.RootViewController;
while (vc.PresentedViewController != null)
{
vc = vc.PresentedViewController;
}
_adInterstitial.PresentFromRootViewController(vc);
}
};
_adInterstitial.LoadRequest(request);
}
}
Calling interstitial ad on PCL page.
DependencyService.Get<IAdmobInterstitial>().Show("(id will come here)");
Navigation.PushAsync(new Page());
Ad is showing perfectly but with a delay. I want to show the ad first and then the page.

So i just solved this.
Here is the code.
PCL Class. Add another function to your interface.
public interface IAdmobInterstitial
{
void Show(string adUnit);
void Give();
}
Droid code. Put _ad.Show() in the new function.
public class InterstitialAdListener : AdListener
{
readonly InterstitialAd _ad;
public InterstitialAdListener(InterstitialAd ad)
{
_ad = ad;
}
public override void OnAdLoaded()
{
base.OnAdLoaded();
//if (_ad.IsLoaded)
// _ad.Show();
}
}
public class AdmobInterstitial : Controls.IAdmobInterstitial
{
InterstitialAd _ad;
public void Show(string adUnit)
{
var context = Android.App.Application.Context;
_ad = new InterstitialAd(context);
_ad.AdUnitId = adUnit;
var intlistener = new InterstitialAdListener(_ad);
intlistener.OnAdLoaded();
_ad.AdListener = intlistener;
var requestbuilder = new AdRequest.Builder().AddTestDevice("302E90D530B2193F59FDD7F22A11B45A");
_ad.LoadAd(requestbuilder.Build());
}
public void Give()
{
if (_ad.IsLoaded)
_ad.Show();
}
}
Now, call the function Show() in the constructor of your MainPage in PCL and call the function Give() when you press the button for the next page.
public MainPage()
{
InitializeComponent();
DependencyService.Get<IAdmobInterstitial>().Show("ca-app-pub-3940256099942544/1033173712");
}
private void button_Clicked(object sender, EventArgs e)
{
DependencyService.Get<IAdmobInterstitial>().Give();
Navigation.PushAsync(new Percentage());
}
This is only for Android. Same goes for iOS as well.
I hope it helps the other programmers. :)

Xamarin C# MainAvtivity.Intent is null

I'm Creating a Call Diverting app using Xamarin. What i am doing is with the press of a button a command is triggerd and using DependencyService i call the Android specific implementaion of the Call Diverter Method.
Now I'm having a problam where the instance of the MainActivity Context for the StartActivity Method is null. I'm suspecting that this is the cause of the error i get when i running the app: 'Target of StartActivity is null (NullReferenceException)'
but i dont know how to fix this. i thought i'm doing everything right but i'm getting an exception.
this is my code so far: Android Project Call diverting method implementation
[assembly: Dependency(typeof(CallDiverter_Android))]
namespace CallDiverter2.Droid
{
public class CallDiverter_Android : ICallDiverter
{
public void DivertCall(string callForwardString)
{
var context = MainActivity.Instance;
//Divert call code
try
{
//String callForwardString = "**21*1234567890#";
Intent callIntent = new Intent(Intent.ActionCall); // ACTION_CALL
Android.Net.Uri uri = Android.Net.Uri.Parse(callForwardString);
callIntent.SetData(uri);
context.StartActivity(callIntent);
//Forms.Context.StartActivity(callIntent);
}
catch (Exception)
{
throw;
}
}
public void StopCallDiverting()
{
//Stop the call diverting action
}
}
}
The instance in the MainActivity class:
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
internal static MainActivity Instance { get; private set; }
protected override void OnCreate(Bundle bundle)
{
Instance = this;
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(bundle);
global::Xamarin.Forms.Forms.Init(this, bundle);
LoadApplication(new App());
}
}

Android C#:Listening for Volume button presses in background service

I'm creating an Android App in C# Xamarin.
Is there a way to "listen" for volume up/down key presses when an App goes into "background" mode, i.e. when a user "locks" their phone?
I've created several Service objects and made them "resident" by issuing the command 'StartCommandResult.Sticky'.
Any sample C# Xamarin code would be much appreciated.

You do not need to create a background service, just start a another task to listen the volume control. If the application do not be killed the task will run on the background.
public class MainActivity : Activity
{
private int currentVolume;
public AudioManager mAudioManager;
private int maxVolume;
private bool isDestory;
Android.Media.MediaPlayer player;
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
player = Android.Media.MediaPlayer.Create(this, Resource.Raw.SampleAudio);
SetContentView (Resource.Layout.Main);
mAudioManager = (AudioManager)GetSystemService(Context.AudioService);
maxVolume = mAudioManager.GetStreamMaxVolume(Stream.Music);
onVolumeChangeListener();
player.Start();
}
protected override void OnDestroy()
{
base.OnDestroy();
isDestory = true;
}
private Task voluemChangeTask;
public void onVolumeChangeListener()
{
currentVolume = mAudioManager.GetStreamVolume(Stream.Music);
voluemChangeTask = new Task(ChangeVolume);
voluemChangeTask.Start();
}
public void ChangeVolume()
{
while (!isDestory)
{
int count = 0;
try
{
Thread.Sleep(20);
}
catch (Exception e)
{
}
if (currentVolume < mAudioManager.GetStreamVolume(Stream.Music))
{
System.Console.WriteLine("volunm+");
count++;
currentVolume = mAudioManager.GetStreamVolume(Stream.Music);
mAudioManager.SetStreamVolume(Stream.Music, currentVolume, VolumeNotificationFlags.RemoveSoundAndVibrate);
}
if (currentVolume > mAudioManager.GetStreamVolume(Stream.Music))
{
System.Console.WriteLine("volunm-");
count++;
currentVolume = mAudioManager.GetStreamVolume(Stream.Music);
mAudioManager.SetStreamVolume(Stream.Music, currentVolume, VolumeNotificationFlags.RemoveSoundAndVibrate);
}
}
}
}
I have tested it in the real device with screen lock and got the log:

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();
}