title: MVVM and Custom Controls?
body: <p>I'm working on PRISM application with modules, MVVM and so on. I understand PRISM pretty good now and I understand value of MVVM. All those things good to deliver <strong>business value</strong> which comes from testability, "uniformity" and so on.</p>
  
  <p>But now I'm stuck with certain interaction issues. I already spent hours and hours trying to see how I set focus in Silverlight via MVVM. All this additional behaviors, attached properties, triggers. It just seems like bunch of junk code with MVVM being root cause.</p>
  
  <p>For example, I need to create Lookup control which is basically textbox with button and popup window. This control itself needs lot of focus control, it needs to overlay view over parent (popups) and so on. It seems to be pretty easy to create it with code-behind, stick it into separate library and move on. My business forms will use this control inside my nice MVVM PRISM.</p>
  
  <p>So, question is.. Is it justified to use code-behind in isolated islands like controls and keep MVVM and TDD for actual code that brings business value?</p>
  
  <p>Is there line where you say "MVVM is not going to be used here" ?</p>