MVVM视图模型参考视图

Question

I am required to use the mvvm pattern. I know that the viewmodel should not care about the view from what I been reading. As a result I don't know how to solve this problem:

I have a dll that basically turns a textbox and listview into an autocomplete control:

SomeDll.InitAutocomplete<string>(TextBox1, ListView1, SomeObservableCollection);

anyways I don't know how to call that method from the viewmodel using the mvvm patter. if I reference the controls in the view I will be braking the rules.

I am new to MVVM pattern and my company requires me to follow it. what will be the most appropriate way of solving this problem?

I know I will be able to solve it by passing the entire view to the viewmodel as a constructor parameter but that will totaly break the mvvm pattern just because I need to reference two controls in the view.

Answer 1

What you're doing here is a pure view concern, so I'd recommend doing it in the view (ie the code-behind). The view knows about the VM and its observable collection, so why not let the code behind make this call?

(I'd also recommend seeing if you can get a non-code/XAML API for "SomeDll", but I have no idea how much control you might have over that)

Answer 2

There are two things that I'd point out here -

First, this is effectively all View-layer code. As such, using code behind isn't necessarily a violation of MVVM - you're not bridging that View->ViewModel layer by including some code in the code behind, if necessary.

That being said, this is often handled more elegantly in one of two ways -

1. You could wrap this functionality into a new control - effectively an AutoCompleteTextBox control. This would allow you to include the "textbox" and "listview" visual elements into the control template, and bind to the completion items within Xaml.

2. You could turn this into an attached property (or Blend behavior), which would allow you to "attach" it to a text box, and add that functionality (all within xaml). The items collection would then become a binding on the attached property (or behavior).