Launching a Viewmodel inside a Timer elapsed not working

Question

I am trying to launch another view model inside a timer event. When I skipped this timer event, it seems that the launcher is being used fine. However, if the launch is done during within the event it doesn't. Can someone please see where the problem is?

using System.Timers;
using Caliburn.Micro.Xamarin.Forms;
using MyProject.Resources;
using System.Windows.Input;
using Xamarin.Forms;
using System.Diagnostics;

namespace MyProject.ViewModels
{
    public class PairingDeviceViewModel : BaseScreen {
    public INavigationService NavigationService { get; set; }

    private Timer timer;
    private const float MAX = 20;
    private string percentage;
    private float rate;

    public float Rate { get => rate; set => Set(ref rate, value); }
    public string Percentage { get => percentage; set => Set(ref percentage, value); }


    protected override void OnInitialize()
    {
        base.OnInitialize();

        timer = new Timer
        {
            Interval = MAX,
        };
    }

    protected override void OnActivate()
    {
        base.OnActivate();
        timer.Elapsed += Timer_Elapsed;
        timer.Start();
    }

    protected override void OnDeactivate(bool close)
    {
        base.OnDeactivate(close);
        timer.Elapsed -= Timer_Elapsed;
    }

    private void Timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        Debug.WriteLine($"Timer_Elapsed");
        Debug.WriteLine($"Rate {Rate}");
        Rate++;
        Percentage = string.Format(StringResources.PercentageNumber, Rate);
        NotifyOfPropertyChange(() => Percentage);
        if (Rate == MAX)
        {
            timer.Stop();
            Debug.WriteLine($"navigation begins");
            NavigationService.NavigateToViewModelAsync<ConfigurationListViewModel>();
        }
        Debug.WriteLine($"Timer_Elapsed END");
    }

    public ICommand SkipBluetoothScanning => new Command(() => {
        timer.Stop();
        NavigationService.NavigateToViewModelAsync<ConfigurationListViewModel>();
    });
}

So on my Timer_elapsed method, I am calling the NavigationService.NavigateToViewModelAsync<>.. once the Rate is equal to MAX. The problem with this one is that this condition Rate==MAX has been called more than once.

Please see the log file.

Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Timer_Elapsed
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Rate 0
Timer_Elapsed END
Timer_Elapsed
Rate 11
Timer_Elapsed END
Timer_Elapsed
Rate 12
Timer_Elapsed END
Timer_Elapsed
Rate 13
Timer_Elapsed END
Timer_Elapsed
Rate 14
Timer_Elapsed END
Timer_Elapsed
Rate 15
Timer_Elapsed END
Timer_Elapsed
Rate 16
Timer_Elapsed END
Timer_Elapsed
Timer_Elapsed END
Rate 17
Timer_Elapsed
Rate 18
Timer_Elapsed END
Timer_Elapsed
Rate 19
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
navigation begins
Timer_Elapsed END
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
Timer_Elapsed END
Timer_Elapsed END
Timer_Elapsed END
Timer_Elapsed END
Timer_Elapsed END
Timer_Elapsed END
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
Timer_Elapsed END
Timer_Elapsed END
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
Timer_Elapsed END
Timer_Elapsed END
[InputMethodManager] HSIFW - flag : 0 Pid : 6116
Timer_Elapsed END

Is DispatcherTimer a better solution for this or another feature if ever?

Thanks a lot.

first, comparing floats with "==" is risky. If you are incrementing by 1 it would be better to use ints. Also, the default interval for timer is 100ms, is that really the granularity you need? — Jason, May 29 '19 at 14:59
I can increase the timer.interval. It should be ok for me. And since the Timer.Interval is a float, this is why I used the Rate as a float as well. The problem I have is that the condition `if(Rate == Max) is being called many times. — Paula Kristin, May 29 '19 at 15:03
https://stackoverflow.com/questions/1530069/comparing-floating-point-values%3E — Jason, May 29 '19 at 15:05
Thanks Jason. Is this the only possible reason why the `NavigateToViewModelAsync` isn't called? — Paula Kristin, May 29 '19 at 15:13
Actually I also have to do this as well to make it complete. if (Math.Abs(Rate - MAX) < double.Epsilon). Please add it to your solution so I can mark it as the answer. Thanks! — Paula Kristin, Jun 03 '19 at 08:13

Leo Zhu · Accepted Answer · 2019-06-03T08:17:42.337

1

you could lock the thread to avoid duplicate execution like this:

private void Timer_Elapsed(object sender, ElapsedEventArgs e)
  {
     lock (this)
        {
         if (Math.Abs(Rate - MAX) < double.Epsilon){
             //something you want to do
               ...
            }
        }
  }

edited Jun 03 '19 at 08:17

answered May 30 '19 at 02:11

Leo Zhu

15,726
1
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Thanks, I will try it out. – Paula Kristin May 31 '19 at 09:34

Launching a Viewmodel inside a Timer elapsed not working

1 Answers1