Run the methods in background which are in ViewModels in Xamarin.ios - ios

Question

I am working on Xamarin.iOS application. I want some part of my currently running features should also run in background. I have a System.Timer which is in the App.cs(Load on start) and added TimerElapsed event in one of the viewcontroller through which control passes to ViewModel on timer elapsed and executes all function.
Now I want the same feature should run in background also but unable to get thoughts how to achieve it. Can anyone help me on this?
Thanks.

Answer 1

The simplest way to do it would be something like this
//Some async method
await Task.Run(async () =>
{
// Code you want to run asynchronously
});
Goodluck!
In case of queries revert!

Answer 2

Backround (when you send your application to background with home button) is a little bit complicated in IOS. You can achive in several ways
1) beginBackgroundTaskWithExpirationHandler but it has some limitation with time
2) locationUpdate event - but with timer it will work not very good. it more suteble when you need check something frome time to time
3) Make you app Player. Player can work even if it is in background
Im using method 3, and it works fine for me
You need add permission for background audio in plist file
<key>UIBackgroundModes</key>
<array>
<string>audio</string>
</array>
Then in your AppDelegate you need modify FinishedLaunching method
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
...
var currentSession = AVAudioSession.SharedInstance();
currentSession.SetCategory(AVAudioSessionCategory.Playback, AVAudioSessionCategoryOptions.MixWithOthers);
currentSession.SetActive(true);
...
}
And add next section, I also put it in AppDelegat
#region Background Work
private BackgroundTask _backgroundTask;
private readonly Lazy<TouchLogger> _logger = new Lazy<TouchLogger>(() => new TouchLogger());
public override void DidEnterBackground(UIApplication uiApplication)
{
base.DidEnterBackground(uiApplication);
startBackgroundTask();
}
public override void WillEnterForeground(UIApplication uiApplication)
{
base.WillEnterForeground(uiApplication);
if (_backgroundTask == null)
{
_backgroundTask = new BackgroundTask(_logger.Value);
}
else if (_backgroundTask.IsRunned)
{
_backgroundTask.Stop();
_logger.Value.Info("Background", "Task stopped");
}
}
private void startBackgroundTask()
{
_logger.Value.Info("Background", "startBackgroundTask() called");
var needBackgroundActivity = true;// if you timer is running set true, if not false
if (needBackgroundActivity)
{
if (_backgroundTask == null)
_backgroundTask = new BackgroundTask(_logger.Value);
_backgroundTask.Start();
_logger.Value.Info("Background", "Task runned");
}
}
private class BackgroundTask
{
private const string EmptySoundFileName = "Sounds/empty";//wav file, I use 4 sec long file with no sound
private TouchLogger _logger;
private AVAudioPlayer _player;
private NSTimer _debugTimer;
public bool IsRunned { get; private set; }
public BackgroundTask(TouchLogger logger)
{
_logger = logger;
}
public void Start()
{
IsRunned = true;
if (_player != null && _player.Playing)
{
Stop();
}
var bundle = NSBundle.MainBundle.PathForResource(EmptySoundFileName, "wav");
var sound = new NSUrl(bundle);
_player = AVAudioPlayer.FromUrl(sound);
_player.NumberOfLoops = -1;
_player.Volume = 0.1f;
_player.PrepareToPlay();
_player.Play();
startDebugTimer();
}
public void Stop()
{
IsRunned = false;
if (_player != null && _player.Playing)
{
_player.Stop();
_player.Dispose();
_player = null;
}
stopTimer(ref _debugTimer);
}
private void startDebugTimer()
{
initAndStartTimer(ref _debugTimer, 5,
() => _logger.Value.Info("Background", "Background is fine!"));
}
private void initAndStartTimer(ref NSTimer timer, int intervalMin, Action action)
{
timer?.Invalidate();
if (action != null)
timer =
NSTimer.CreateRepeatingScheduledTimer(
TimeSpan.FromMinutes(intervalMin),
t => action());
}
private void stopTimer(ref NSTimer timer)
{
timer?.Invalidate();
timer = null;
}
}
#endregion
TouchLogger - send some messages to console, for checking background, you can remove it. Same with _debugTimer, it just write state of background worker avery 5 min.
If something not working tell me, i did it long time ago, so maybe missed something