Skip to main content

Observable.Timer throws ArgumentOutOfRangeException

We found this one out during testing in different time zones earlier this - if your app is going used in different time zones avoid using DateTime with Observable.Timer. In fact I guess the general message should be avoid DateTime all together in any apps use DateTimeOffset instead...

This code works from here in London but when run in Hong Kong throws an exception:

   1:  static void Main(string[] args)
   2:  {
   3:      var now = DateTimeOffset.Now;
   4:      Console.WriteLine("Time zone offset: " + now.Offset);
   5:   
   6:      var scheduler = NewThreadScheduler.Default;
   7:   
   8:      using(Observable.Timer(DateTime.MinValue, TimeSpan.FromSeconds(1), scheduler)
   9:          .Subscribe(Console.WriteLine))
  10:      {
  11:          Console.ReadLine();
  12:      }            
  13:  }

London time zone shows output as expected:
Where as when run for a time zone set to anything positive of London (offset = 0), e.g. Hong Kong (offset =  +8) you get an exception:
If you want to know why this is happening check out @leeoades post here, but simply because DateTime supports an implicit conversation to DateTimeOffset and the value is invalid after conversation this is why we're seeing this happen.

So it can be fixed easily enough by using any of the following alternatives:

   1:  Observable.Timer(DateTimeOffset.MinValue, TimeSpan.FromSeconds(1));
   2:   
   3:  // or...
   4:   
   5:  Observable.Timer(DateTimeOffset.Now, TimeSpan.FromSeconds(1));
   6:   
   7:  // or...
   8:   
   9:  var scheduler = NewThreadScheduler.Default;
  10:  Observable.Timer(scheduler.Now, TimeSpan.FromSeconds(1), scheduler);

I prefer the final alternative, it's better suited for testing because the scheduler can be mocked out and you can control the value of the Scheduler.Now.

Comments

Popular posts from this blog

Implementing a busy indicator using a visual overlay in MVVM

This is a technique we use at work to lock the UI whilst some long running process is happening - preventing the user clicking on stuff whilst it's retrieving or rendering data. Now we could have done this by launching a child dialog window but that feels rather out of date and clumsy, we wanted a more modern pattern similar to the way <div> overlays are done on the web. Imagine we have the following simple WPF app and when 'Click' is pressed a busy waiting overlay is shown for the duration entered into the text box. What I'm interested in here is not the actual UI element of the busy indicator but how I go about getting this to show & hide from when using MVVM. The actual UI elements are the standard Busy Indicator coming from the WPF Toolkit : The XAML behind this window is very simple, the important part is the ViewHost. As you can see the ViewHost uses a ContentPresenter element which is bound to the view model, IMainViewModel, it contains 3 child v

Showing a message box from a ViewModel in MVVM

I was doing a code review with a client last week for a WPF app using MVVM and they asked ' How can I show a message from the ViewModel? '. What follows is how I would (and have) solved the problem in the past. When I hear the words ' show a message... ' I instantly think you mean show a transient modal message box that requires the user input before continuing ' with something else ' - once the user has interacted with the message box it will disappear. The following solution only applies to this scenario. The first solution is the easiest but is very wrong from a separation perspective. It violates the ideas behind the Model-View-Controller pattern because it places View concerns inside the ViewModel - the ViewModel now knows about the type of the View and specifically it knows how to show a message box window: The second approach addresses this concern by introducing the idea of messaging\events between the ViewModel and the View. In the example below

Custom AuthorizationHandler for SignalR Hubs

How to implement IAuthorizationRequirement for SignalR in Asp.Net Core v5.0 Been battling this for a couple of days, and eventually ended up raising an issue on Asp.Net Core gitHub  to find the answer. Wanting to do some custom authorization on a SignalR Hub when the client makes a connection (Hub is created) and when an endpoint (Hub method) is called:  I was assuming I could use the same Policy for both class & method attributes, but it ain't so - not because you can't, because you need the signatures to be different. Method implementation has a resource type of HubInnovationContext: I assumed class implementation would have a resource type of HubConnectionContext - client connects etc... This isn't the case, it's infact of type DefaultHttpContext . For me I don't even need that, it can be removed completely  from the inheritence signature and override implementation. Only other thing to note, and this could be a biggy, is the ordering of the statements in th