Question

I have this class to run functions in some amount of time:

namespace Test
{
    public static class At
    {
        private static void ExecuteDelayedAction(object o)
        {
            (o as Action).Invoke();
        }

        public static void Do(Action action, TimeSpan delay, int interval = Timeout.Infinite)
        {
            new Timer(new TimerCallback(At.ExecuteDelayedAction), action, Convert.ToInt32(delay.TotalMilliseconds), interval);
        }
        public static void Do(Action action, DateTime dueTime, int interval = Timeout.Infinite)
        {
            if (dueTime >= DateTime.Now) Do(action, dueTime - DateTime.Now, interval);
        }
        public static void Do(Action action, int delay, int interval = Timeout.Infinite)
        {
            Do(action, TimeSpan.FromMilliseconds(delay), interval);
        }
    }
}

And also in my application I have two pages – Login.xaml and MainPage.xaml. Just for test purposes I’ve puth the following code in MainPage constructor:

public MainPage()
{
    InitializeComponent();
    At.Do(delegate { Debug.WriteLine("MainPage"); }, 5000);
}

My problem is as follows: if application opens MainPage first then timer works fine and delegate gets executed. If, however, application opens Login first and then navigates to MainPage then timer just fails silently. Why is it happening and how can it be fixed?

Answer 1

I suspect that the timer you are creating is being garbage-collected (GC’ed), as you are not holding a reference to it anywhere but just dropping the reference to the newly created timer.

As navigating between pages will cause quite a bit of memory to be created, a GC may be triggered then.

Try fixing it by keeping a reference to the timer object around. I would create a Do class instance which you could hide a private timer inside, and keep a reference to that. However if you want to keep your current static class design you could just return an object that is the timer.

    public static object Do(Action action, TimeSpan delay, int interval = Timeout.Infinite)
    {
        var t = new Timer(new TimerCallback(At.ExecuteDelayedAction), action, Convert.ToInt32(delay.TotalMilliseconds), interval);
        return t;
    }

and then you need to store a reference to your timer with your page.

public MainPage()
{
    InitializeComponent();
    this.doObject = At.Do(delegate { Debug.WriteLine("MainPage"); }, 5000);
}

Of course, if the MainPage is GC’ed then your timer will be too, but you can fix that by changing the scope of your timer to what is appropriate for the action you want to run.