Question

I’m creating custom control and because I need to do lot’s of binding inside a style/template it makes perfect sense to go with MVVM. Where do I declare dependency properties then?

Do they stay in control class? How do I link them to VM?

Answer 1

See my answer to your other question about custom controls and view models. Here’s the short version:

1. Custom controls shouldn’t have view models.
2. Don’t set the data context of your own control. That’s reserved for the consumer.
3. All of your dependency properties should be declared in your MyCustomControl.cs file.
4. Use TemplateBinding in your genric.xaml because it’s more efficient that Binding.

To put it another way, what’s the view model for a Border or a Button? Answer: they don’t have one because they’re just controls. UserControls have view models, but controls just present and interact with the data which you give them (where? In your UserControl). Custom control development is probably the hardest thing for a seasoned MVVM developer: your reflex is to make a view model, but that reflex is unfortunately wrong. I know because I’ve made this mistake myself.