Talk Nerdy To Me

I’ve recently started experimenting with NHibernate – the C#/.NET version of the Hibernate O/R matpping tool that was originally developed for Java. The Java version is very powerful, and I’m a huge fan of it. The C#/.NET version is, for the most part, a straight port of the Java code base (and an ugly port, in some ways). Nevertheless, it appears to be just as robust as its predecessor.

Be warned, however, that the NHibernate DLLs require a high level of trust in the ASP.NET environment they’re deployed to. I spent an entire weekend beating my head against a wall trying to get a simple app up on my GoDaddy account. I suspect NHibernate probably wasn’t designed with a medium trust environment in mind. I was able to make a few tweaks to get the code running with fewer permissions requirements. However, the permissions required to enable dynamic proxies – a fundamental part of the NHibernate architecture – are non-negotiable.

I learned from GoDaddy tech support that their Deluxe Windows plan, a shared host environment, simply doesn’t allow those permissions. I’d need to upgrade to a dedicated server, and that’s just a little too pricey for an environment simply for experimentation. I was able to get NHibernate working without any hacks at Webhost4life, but I thought I’d share what I tried first at GoDaddy just to help you understand the permissions implications if you’re in a medium trust environment — and how you might need to address them on your own projects.

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Vincenty’s Formula is an iterative solution for calculating the distance and direction between two points along the surface of Earth. For clarity, I’ve stripped out portions of the code I’ve put up for discussion, but you can download the entire C# source code from here. If you prefer Java, please see the Java version of this discussion.

Several years ago, I stumbled on a great pastime called “geocaching.” It’s a worldwide treasure hunting game where participants use handheld GPS receivers to find hidden “caches” - small boxes filled with prizes, trinkets, and “travel bugs“. The caches are hidden by other participants who post nothing more than the latitude and longitude on a website like Geocaching.com. My children and I have had a blast. It’s a great way for a grown man to justify playing in the woods (and buying an expensive gadget!) under the pretense of “playing with the kids.” With over 420,000 caches in 222 countries on all continents (including Antarctica!) there are bound to be several near you.

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Here’s a nasty bug that crept into one of my team’s projects recently. When will equivalent C# objects fail to compare as equal? The answer is “when operator== doesn’t work as expected.”

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All you geniuses and rocket scientists out there probably already know this, but I just stumbled on it, and I think it’s kind of cool. Did you know you can customize the adding and removing of C# event handlers? I didn’t.

I’m going to end this post with the question “Yes, but what’s it good for?” You folks with the Ph. D. in C#, feel free to scroll to the bottom and post your answers. For my fellow mortals out there, let me recap what I’m talking about.

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Okay, so I blogged about how C# BindingList<T> serialization is broken and how to fix it. The problem centers around filling a BindingList subtype with items that implement INotifyPropertyChanged. This enables your list to fire ListChanged events indicating ItemChanged whenever a property of a list item changes. Unfortunately, serializing and deserializing the list causes the ItemChanged notification to stop firing unless you take steps to properly rebuild the list. This happens because C# event handlers aren’t serializable, and .NET fails to rewire the listeners.

A colleague of mine asked for a quick example to demonstrate the problem, so I whipped up this test case.

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I previously blogged about how to use the C# INotifyPropertyChanged interface with BindingList<T> instances so that your lists properly fire the ListChanged event with a ListChangedType of ItemChanged.

In that post, I also alluded to the fact that BindingList<T> is flawed with regard to serialization of BindingList<T> subtypes. The problem has to do with the fact that BindingList<T> listens for PropertyChanged events on any of its list items that implement INotifyPropertyChanged. However, because event handlers are not serializable, those listener connections are lost during the serialization process for subtypes, and they don’t get rewired when the list is deserialized. It’s straightforward to do that, but the implementation is missing from the .NET SDK, so we have to write it ourselves.

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After reading Bil Simser’s discussion on DataTable vs. BindingList<T>, I’m convinced that BindingList<T> is the way to go for representing domain objects in C#. However, effective use of BindingList does require a certain amount of planning and forethought on the part of the developer. There are a number of things you can do to increase your chances of success with BindingList, but this post is about having your list items implement INotifyPropertyChanged in order to propagate change events through the BindingList itself.

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