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February 22, 2012 mgroves 0 Comments
Tags: INotifyPropertyChanged Cecil MSBuild NotifyPropertyWeaver

One of the problems with object-oriented programming that AOP aims to solve is excessive boilerplate. And there's no more stark example of excessive boilerplate than the use of INotifyPropertyChanged.

NotifyPropertyWeaver is a tool that adds an MSBuild task to your project. It will find all your implementations of INotifyPropertyChanged and rewrite the properties to do all the notification code for you. So you don't have to worry about mistyping that property name string, and you don't have to worry about refactoring when you rename or remove properties.

In this code example below, the first file is a typical implementation of INotifyPropertyChanged, done entirely by hand. Notice all the noise and duplication: explicit backing properties, multiple calls to NotifyPropertyChanged to account for the derived property, the use of a string that exactly matches the property names. And this is a class with only three properties. Imagine if you had a whole bunch more properties, and imagine the maintenance problem to add/remove/change one of the derived properties!

The second file is an example of how you would do the exact same thing using NotifyPropertyWeaver. You don't have to write the NotifyPropertyChanged method, or call it in the setters, or write backing properties. This class is so much easier to read and maintain. The third file is actually a look at the class after it's been compiled, run through NotifyPropertyWeaver, and then disassembled with Telerik's JustDecompile. Look familiar? It's almost exactly the same as the hand-coded implementation.

And finally, the fourth file is the change that will be made to your project file when you add NotifyPropertyWeaver with NuGet. It calls a task that uses Mono.Cecil to rewrite the code for you. You don't need to reference the build task DLL in your project.

NotifyPropertyWeaver is a tool that does a single task, but this approach (an MSBuild post-compiler task) can be used to implement other AOP features. Fody is a tool by the creator of NotifyPropertyWeaver to do just that.


Matthew D. Groves

About the Author

Matthew D. Groves lives in Central Ohio. He works remotely, loves to code, and is a Microsoft MVP.

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