title: how to asynchronously update viewmodel property based on selection of another property
body: <p>Say I have some kind of list control in the view from which I select a name and this sets a 'SelectedName' property in the viewmodel.  When a name is selected I then want to asynchronously fetch a set of data associated with that name and set another property with that data which will then update another control in the view bound to that other data property.</p>
  
  <p>Can't use async/await with properties so can't make the request and assignment in the 'SelectedName' setter.</p>
  
  <p>What is MVVM best practice for this case?</p>
  
  <p>I was thinking maybe the selection of name could also trigger execution of a command (RelayAsyncCommand) in the viewmodel which could do the async fetch and assignment work. But is there any guarantee that the 'SelectedName', which would be needed by the command, would be updated before the command executes? </p>