Question

I am currently writing a Particle System using XNA. What I’d like to do is use an external file (XML for example) and be able to modify this file, whilst the application is running, and once saved, the changes will be reflected in the Particle System.

My original proposal:
Use a FileWatcher (can’t remember the exact class name) to monitor the particle effect file and when the date changes, reload the file thus causing the changes to be made.

Any help would be appreciated.

Answer 1

You are on the right track.

Create a System.IO.FileSystemWatcher.
Subscribe to the Changed event.

When the Changed event occurs
   If the path/file extension corresponds to a buildable resource type
      Either
         Directly create and invoke a content importer and processor. (Xna 4.0)
      Or
         Use MSBuild to build a dummy content project.
      
      Replace references to the existing resource with the newly built resource
      Dispose of the old resource if necessary

Notes:

• The FileSystemWatcher sometimes
  generates multiple change events for
  a single change. Also, some
  programs, like photoshop save to a
  temporary file, then delete the
  original and rename the temporary
  file to the original name. My system
  buffers file system events and
  combines them into single events
  where possible. Because they are
  buffered this also allows me to apply
  the events to the content at an
  appropriate point in the program. If
  you don’t buffer these events could
  trigger while the resource you are
  trying to replace is in use.

• Shawn Hargreaves has written about Effect compilation and Content Pipeline automation in XNA Game Studio 4.0.

• AppHub has a Code Snippet WinForms Series 2: Content Loading which shows how to use MSBuild to build content dynamically. I have found this method is slower than invoking the importer and processor directly.

• In my system, all references to dynamic resources are indirect references. These indirect references are allocated and tracked by a resource manager. When a resource is dynamically built the resource manager replaces the actual reference inside the indirect reference. A resource changed event is generated through the indirect reference so clients can take action if required.