title: Visual Studio: "This document is opened by another project"
body: <p>I spend most of my time developing controls for both WPF and Silverlight using the same codebase. To do this I add existing files from one project (say Silverlight) "as links" to the other (say WPF). For minor differences I use preprocessor directives like</p>
  
  <pre><code>#if SILVERLIGHT
  ...
  #else
  ...
  #endif
  </code></pre>
  
  <p>The code in these blocks is grayed out depending on the type of project you've opened the file from. So if you open your file from Silverlight project (where SILVERLIGHT is defined) the else part is gray and Intellisense doesn't work in it.</p>
  
  <p>In order for WPF part to be processed by IDE (with coloring and Intellisense support) you need to open the file from the WPF project. When you try to do that you get a message box saying that <strong>"This document is opened by another project"</strong> and when you click OK it displays that file in the context of the Silverlight project (not what I wanted to see). So I have to close the file, navigate to WPF project again and open the file again. This is very, very annoying.</p>
  
  <p>So the question is this: is there some sort of setting or add-on that would make Visual Studio reopen the file from the project where I double-clicked on it instead of showing that stupid message box and showing me that file from the "wrong" project?</p>