title: UI action in middle of MvxCommand
body: <p>I am using MvvmCross, but this may be general command binding.</p>
  
  <p>When user click a button, the application require an extra input data before proceed to what I want to do in the actual command. The problem that I cannot call an UI action in middle of ViewModel, so just binding MvxCommand (or any ICommand) would not work.</p>
  
  <p>One may ask  why:
  1) I don't put an input on the UI and user can enter data before click button -> I don't have space.
  2) Make default data, and let user change it later -> This my first though, but user tend to forget to change it later!!</p>
  
  <p>So can someone come up with a solution? The only thing I can think of is forgetting command binding, and have code behind pop the ui for extra data, then call a method in view model!</p>
  
  <p>Thanks</p>