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Bindings Not Updating in WPF / Silverlight? Common Mistakes

Introduction

Yesterday I was working on a small prototype, which I will be blogging about shortly, and ran across the common problem of my bindings not updating. A very common problem, and one that’s usually a very simple fix once you’ve tracked it down.

Yes, I’m an Idiot!

Normally my ViewModels inherit from my ViewModelBase base class, which provides a RaisePropertyChanged method and, when in debug mode, uses reflection to check if the property name is valid. Now I’d recently refactored the code so this particular ViewModel wasn’t using the base class, so my first instinct was that I’d simply mistyped the property name magic string in the event – but that was all fine.

I threw in a few breakpoints and I could see my ViewModel was changing, I could see the OnPropertyChanged method being hit, but there didn’t seem to be any listeners and as a result my UI was just ignoring the changes.

After a few minutes of head scratching I noticed that although my class was firing the PropertyChanged event correctly, I hadn’t added INotifyPropertyChanged to my class declaration when I removed the base class! So although I was firing an event that looked like INotifyPropertyChanged.PropertyChanged, I was actually just firing my own event with the same name :-)

Conclusion

So there you have it, I’m an idiot :-) The moral of the story is, when your bindings aren’t working check the obvious:

  1. The property name is correct. A base class that checks this in debug mode can be useful, or failing that, watch the Output window.
  2. Check you are actually implementing INotifyPropertyChanged and not just firing events that happen to have the same name :-)
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Posted in Silverlight, WPF.

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