AutoCAD 2016: Calling commands from external events using .NET

Last week we introduced the ExecuteInCommandContextAsync() method and saw it in action from a context menu click event. In today’s post we’re going to see how it can be used for a lot more: we’re going to use it to respond to external, operating system-level events (although admittedly we’re handling the event in-process to AutoCAD via .NET).

What we’re actually going to do is fire off a command inside AutoCAD – in our case we’re going to use RECTANG to create square polylines – each time we find that a file has been placed in a particular folder (in our case “c:\temp\files”, although the actually location isn’t particularly important).

Here’s what we’re aiming for – this recording shows AutoCAD on the left and an Explorer window pointed at “c:\temp\files” on the right.

Of course the specific event we’re responding to – in our case the Changed event on a FileSystemWatcher – isn’t really the point. The point is that this mechanism allows you to react to things happening outside AutoCAD, calling AutoCAD commands in reaction.

Here’s the C# code, to show how it’s working. Something to bear in mind… we’re only adding squares until there are as many as files in the tracked folder: more work would be needed to remove squares as files get deleted or moved away. But this is simply an example of hooking such an event into AutoCAD – I didn’t see much point in adding that kind of complexity to the code.

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Runtime;
using System;
using System.IO;
 
namespace CommandFromAppContext
{
  public class Commands
  {
    const int columns = 10;
    const string path = "c:\\temp\\files";
 
    private FileSystemWatcher _fsw = null;
    private int _fileNum = 0;
    private int _filesTotal = 0;
    private bool _drawing = false;
 
    [CommandMethod("EC")]
    public void EventCommand()
    {
      var dm = Application.DocumentManager;
      var doc = dm.MdiActiveDocument;
      if (doc == null)
        return;
 
      var ed = doc.Editor;
 
      // We'll start by creating one square for each file in the 
      // specified location. The nSquares() function uses some
      // global state for the index and the total count
 
      _fileNum = 0;
      _filesTotal = Directory.GetFiles(path).Length;
 
      nSquares(ed);
 
      // Create a FileSystemWatcher for the path, looking for
      // write changes and drawing more squares as needed
 
      if (_fsw == null)
      {
        _fsw = new FileSystemWatcher(path, "*.*");
        _fsw.Changed += (o, s) => nSquaresInContext(dm, ed, path);
        _fsw.NotifyFilter = NotifyFilters.LastWrite;
        _fsw.EnableRaisingEvents = true;
 
        ed.WriteMessage("\nWatching \"{0}\" for changes.", path);
      }
    }
 
    [CommandMethod("ECX")]
    public void StopEventCommand()
    {
      var dm = Application.DocumentManager;
      var doc = dm.MdiActiveDocument;
      if (doc == null)
        return;
 
      var ed = doc.Editor;
 
      if (_fsw != null)
      {
        _fsw.Dispose();
        _fsw = null;
      }
 
      ed.WriteMessage("\nNo longer watching folder.");
    }
 
#pragma warning disable 1998
 
    private async void nSquaresInContext(
      DocumentCollection dc, Editor ed, string path
    )
    {
      // We'll set the total as it may well have changed (hence the
      // need for global state rather than using an argument)
 
      _filesTotal = Directory.GetFiles(path).Length;
 
      // Protect the command-calling function with a flag to avoid
      // eInvalidInput failures
 
      if (!_drawing)
      {
        _drawing = true;
 
        // Call our square creation function asynchronously
 
        await dc.ExecuteInCommandContextAsync(
          async (o) => nSquares(ed),
          null
        );
 
        _drawing = false;
      }
    }
 
#pragma warning restore 1998
 
    private void nSquares(Editor ed)
    {
      // Draw squares until we have enough (the total might
      // change, hence the need for global state)
 
      for (; _fileNum < _filesTotal; _fileNum++)
      {
        // Determine the position in our grid
 
        int xoff = _fileNum % columns,
            yoff = _fileNum / columns;
 
        // Create our polyline via the RECTANG command
 
        ed.Command(
          "._rectang",
          String.Format("{0},{1}", xoff, yoff),
          String.Format("{0},{1}", xoff + 1, yoff + 1),
          "_regen"
        );
      }
    }
  }
}