NSTimer versus Timer in Xamarin.iOS - when to use what?

Question

Is there a rule when to use the native NSTimer versus the .NET alternatives?

System.Windows.Forms.Timer
System.Timers.Timer
System.Threading.Timer

Stephane Delcroix · Answer 1 · 2013-10-15T07:25:47.883

If you aim for portability, I'd use a .NET timer (see below) except if you have no other choices (like a NSTimer argument for a method call).

My all time favourite timer is unfortunately not listed in your question, is the one offered by the Task class:

await Task.Delay (20);
//do something after the delay

Usage is very simple. So instead of this Timer code:

void f() {
    var timer = new Timer(2000);
    timer.Elapsed += OnTimerElapsed;
    timer.Start ();
    Console.WriteLine ("Timer started, control is back here");
}

void OnTimerElasped (object o, EventArgs e)
{
    Console.WriteLine ("tick");
}

You can use this:

void f() {
    StartTimer ();
    Console.WriteLine ("Timer started, control is back here");
}

async void StartTimer ()
{
    while (true) {
        await Task.Delay (2000);
        Console.WriteLine ("tick");
    }
}

or if you want a single execution:

async void StartTimer ()
{
    await Task.Delay (2000);
    Console.WriteLine ("tick");
}

Which is a real benefit, as you don't need to keep the timer as instance variable just to be able to .Stop() it.

I find this form more streamlined. Just like we dismissed the goto statement years ago (GOTO isn't dead. It's on the island with Elvis and Joe Dassin), it's time to think about our callbacks overuse.

Task.Delay() is not really a timer, is it? I mean, I cannot really schedule things. — Krumelur, Oct 14 '13 at 19:32
I see it, and use it, as a timer. it can schedule code (placed after the await) to be executed. It's just more streamlined, without the need for delegates. — Stephane Delcroix, Oct 14 '13 at 20:00
And a repeating timer would then be while(true) { await Task.Delay(20); }? — Krumelur, Oct 14 '13 at 20:03

score 9 · Answer 2 · edited Nov 17 '17 at 13:57

9

I suggest to use NSTimer.

Xamarin 5.10:

var sampleTimer = NSTimer.CreateRepeatingScheduledTimer (TimeSpan.FromSeconds (5.0), delegate {

    //Write Action Here
                });

and add a line To start the timer!

sampleTimer.Fire();

Stop after use:

    sampleTimer.Invalidate ();
    sampleTimer.Dispose ();
    sampleTimer = null;

edited Nov 17 '17 at 13:57

UserID0908

98
1
15

answered Mar 17 '16 at 09:50

Alvin George

14,148
92
64

Out of interest, what is your reasoning for choosing NSTimer over .net timers? – MattjeS Jun 20 '17 at 13:42

score 6 · Accepted Answer · answered Oct 08 '13 at 12:10

6

IMO the prime rule is that anytime some types (or methods) offers duplicated features between .NET and the platform you're currently working on, you must consider your long term cross-platform goals for your application and that particular bit of code (reuse).

IOW code using NSTimer will only work on iOS and OSX. Using a .NET timer will work on Windows, Android and, of course, iOS and OSX.

answered Oct 08 '13 at 12:10

poupou

43,413
6
77
174

Is it true what James has replied about the auto release pools? – Krumelur Oct 08 '13 at 12:29
1

The ThreadPool already has internal support for `NSAutoreleasePool` and support for `Thread` was added in 5.2, see http://spouliot.wordpress.com/2011/12/01/threading-and-pooling/ OTOH support for `Task` and `BackgroundWorker` still need special support (reusing the same thread needs to drain the pool) http://forums.xamarin.com/discussion/6404/memory-leaks-and-nsautoreleasepool – poupou Oct 08 '13 at 12:51
@poupou +1 I am sure I read about this issue a while ago, wasn't sure it had been addressed. I have deleted my answer based on your documentation link :) – James Oct 08 '13 at 12:57

score 2 · Answer 4 · edited May 23 '17 at 12:02

Some answers recommend using .net timers for cross-platform goals. But the problem is that Timer class is not available in some PCL profiles (at least the profile Xamarin uses). In those cases, the workaround involves using Task.Delay() as @stephane-delcroix suggested. I even created a PclTimer utility class for that matter.

BUT...

I found a situation where Task.Delay() won´t work properly on iOS. If you try to use it within a background task:

var taskId = UIApplication.SharedApplication.BeginBackgroundTask(() => {});
// run your timer logic here with Task.Delay()

you´ll find out that the intervals become corrupted (delayed), not respecting the interval you set on Task.Delay(interval).

In that scenario, NSTimer.CreateRepeatingScheduledTimer() works totally fine.

So I would say:

Do you need to run the timer in a background task? => Use NSTimer
You don´t need background tasks? => use .NET

score 1 · Answer 5 · answered Nov 12 '15 at 16:58

I agree with Poupou and Stephane, but I would also say "it depends". If you need to implement the timer in a common or shared part .Net alternatives are the best. Since the question is about Xamarin.iOS (not Xamarin.Android or Xamarin.Forms) I would like to add the following not listed (so far) solution that works for me and it's very simple.

NSTimer timer = NSTimer.CreateRepeatingScheduledTimer(TimeSpan.FromSeconds(3), delegate { MyMethod(); });

It Calls MyMethod(); every 3 seconds.

NSTimer versus Timer in Xamarin.iOS - when to use what?

5 Answers5