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.
Labels:
Location: London Borough of Hackney, London N16 1AZ, UK

Comments

Post a Comment

Popular posts from this blog

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 ...
5 comments
Read more

WPF tips & tricks: Dispatcher thread performance

Not blogged for an age, and I received an email last week which provoked me back to life. It was a job spec for a WPF contract where they want help sorting out the performance of their app especially around grids and tabular data. I thought I'd shared some tips & tricks I've picked up along the way, these aren't probably going to solve any issues you might be having directly, but they might point you in the right direction when trying to find and resolve performance issues with a WPF app. First off, performance is something you shouldn't try and improve without evidence, and this means having evidence proving you've improved the performance - before & after metrics for example. Without this you're basically pissing into the wind, which can be fun from a developer point of view but bad for a project :) So, what do I mean by ' Dispatcher thread performance '? The 'dispatcher thread' or the 'UI thread' is probably the most ...
Post a Comment
Read more

Managing themes in WPF

Having just published Simple.Wpf.Terminal as a nuget package I wanted the ability to skin the user control - the more flexibility in the way it looks the more likely it will be used by other devs :) Before getting into the detail, lets look at the solution working in the test harness for my WPF F# REPL Engine , shown below are four different themes applied dynamically at run-time - no recompilation required to change the theme: Previously in larger WPF apps I've relied upon third-party control vendors like Telerik to provide theming support. Typically they provide good solutions to the problem with multiple themes supported as standard, and when you're already using their third party controls the use of their themes makes sense. But when you're developing a small UI component you don't want to add (& support) such a large footprint just to add themes to your niche control. A theme is a collection of Styles grouped into a ResourceDictionary in WPF. A ...
Post a Comment
Read more