Auto-refreshing triggered by changes in directory for ArcPy?

Question

I have a directory change monitor python script which monitors any changes happened in a directory, I want to trigger Arcmap auto refreshing whenever a change has been detected (eg. a new line added to a file). I tried to launch the monitor program within arcmap python command window using execfile("myprogram.py"). The problem I encountered is that once the script starts to monitor and auto-refresh, the arcmap main window was locked and frozen, no way to stop it except shutting down the arcmap, although I can see the auto-refresh happened whenever there is a change. Is there a way to run the monitor script in a separate process or background without locking or freezing the main window? Here is my monitor script which is borrowed from Tim Golden,

    import os
    import win32file
    import win32con
    import arcpy

    # Search for the new data
    ACTION = {
       1: "Created",
       2: "Deleted",
       3: "Updated",
       4: "Renamed from something",
       5: "Renamed to something"
    }


    FILE_LIST_DIRECTORY = 0X0001
    path_to_watch = "C:\Directory"

    hDir = win32file.CreateFile(
          path_to_watch,
         FILE_LIST_DIRECTORY,
         win32con.FILE_SHARE_READ | win32con.FILE_SHARE_WRITE |   win32con.FILE_SHARE_DELETE,
         None,
          win32con.OPEN_EXISTING,
          win32con.FILE_FLAG_BACKUP_SEMANTICS,
          None
     )


     while 1:
        results = win32file.ReadDirectoryChangesW(
            hDir,
            1024,
            True,
            win32con.FILE_NOTIFY_CHANGE_FILE_NAME |
            win32con.FILE_NOTIFY_CHANGE_DIR_NAME |
            win32con.FILE_NOTIFY_CHANGE_ATTRIBUTES |
            win32con.FILE_NOTIFY_CHANGE_SIZE |
            win32con.FILE_NOTIFY_CHANGE_LAST_WRITE |
            win32con.FILE_NOTIFY_CHANGE_SECURITY,
            None,
            None
         )

    for action, file in results:
        full_filename = os.path.join(path_to_watch, file)
        print full_filename, ACTION.get(action, "Unknown")
        arcpy.RefreshActiveView()

Answer 1

Here is the absolute nuts and bolts of the method:

IDynamicMap gDynamicMap;
IDynamicDisplay gDynamicDisplay;
FileSystemWatcher eLogWatcher;
bool gLOGchanged = false;

protected override void OnClick()
{
    IMap pMap = ArcMap.Document.FocusMap;
    gDynamicMap = (IDynamicMap)pMap;
    if (!gDynamicMap.DynamicMapEnabled) gDynamicMap.DynamicMapEnabled = true;
    gDynamicMap.DynamicDrawRate = (int)RefreshRate.Value; // set your refresh rate here
    
    // wire dynamic events
    ((IDynamicMapEvents_Event)gDynamicMap).DynamicMapFinished += new IDynamicMapEvents_DynamicMapFinishedEventHandler(OnTimerElapsed);
    ((IDynamicMapEvents_Event)gDynamicMap).AfterDynamicDraw += new IDynamicMapEvents_AfterDynamicDrawEventHandler(OnAfterDynamicDraw);
    
    // start the watcher
    eLogWatcher = new FileSystemWatcher();
    eSnavWatcher.Path = BaseFolderPath.Text + "\\pos";
    eSnavWatcher.Filter = "*.log"; // set this or you'll get events for every file that changes
    eSnavWatcher.NotifyFilter = NotifyFilters.LastWrite; // this too, limit the events
    eSnavWatcher.Changed += new FileSystemEventHandler(eSnavWatcher_Changed);
    eSnavWatcher.EnableRaisingEvents = true;
}
private void OnTimerElapsed(IDisplay Display, IDynamicDisplay dynamicDisplay)
{
    # do some processing in here, the map is already being refreshed
    # it is safe to do nothing here if !gLOGchanged - nothing to do.
    if (gLOGchanged)
    {
        # do your reading here
        gLOGchanged = false; // reset!
    }
}

void OnAfterDynamicDraw(esriDynamicMapDrawPhase DynamicMapDrawPhase, IDisplay Display, IDynamicDisplay dynamicDisplay)
{
    # draw graphics to the screen here
}

void eSnavWatcher_Changed(object sender, FileSystemEventArgs e)
{
    gLOGchanged = true;
}

The key here is the DynamicMap and DynamicDisplay which fires every interval continuously. In order to draw graphics you need to use DynamicSymbols (not standard symbols).

Using a FileSystemWatcher I set a boolean if a file is changed and then with the regular refresh detect that boolean indicating the file has changed. Note: with buffering the file may not change when you think it does, the FileSystemWatcher responds only when the file on disc has changed.

This code comes from a working tool that plots the course of a vehicle in real time (or near enough to) on a notebook to tell if the vehicle is going off course and correct before the data captured is invalid.