MATLAB: File modification alert from windows api

apiimagemodificationtimerupdatewindows

Hello!

I want my matlab program to receive a notification from or through the windows api whenever a file is externally modified (a picture) so that it can immediately load the new file. I am basically trying to avoid using a timer function as that one only looks for changes once a time interval and when i make the interval too small it produces problems.

Thanks!

Best Answer

You may be able to use the .NET interface, using the FileSystemWatcher class.

Here's a simple example in MATLAB (assuming you have an image called "mypicture.jpg" in the current folder:

% Watch this folder
w = System.IO.FileSystemWatcher(pwd);
% Watch a particular image file
w.Filter = 'mypicture.jpg';
% Notify when the file changes
w.NotifyFilter = System.IO.NotifyFilters.LastWrite;
% Create a listener for change
addlistener(w, 'Changed', @changedFcn);
% Start watching.
w.EnableRaisingEvents = true;

You also need to create a function like this:

function changedFcn(obj, eData)
   fprintf('Changed: %s\n', char(eData.FullPath));
end

Try modifying the image.

Related Solutions

MATLAB: Errors with polling directory for new files to process

while true
  clc;    
  warning('off','images:initSize:adjustingMag');
  loadimg = imread(full_filename);
  %processing section
end

This is an infinite loop, which processes the same image again and again. I assume that omitting the "while true" solves the problem directly.

If some warnigns would be shown, clc will hide them soon. Therefore I never use this function, because the output to the command window contains valuable debug information.

Note: Polling wastes some processing time, therefore an callback approach might be more usefull. But I'm not sure how this can be compiled and in works under Windows only:

w = System.IO.FileSystemWatcher(pwd);
% Watch a particular file type:
w.Filter = '*.jpg';
% Notify when the file changes
w.NotifyFilter = System.IO.NotifyFilters.LastWrite;
w.NotifyFilter = System.IO.NotifyFilters.DirectoryName
w.NotifyFilter = w.NotifyFilter Or System.IO.NotifyFilters.FileName
w.NotifyFilter = w.NotifyFilter Or System.IO.NotifyFilters.Attributes
w.IncludeSubdirectories = True
% Create a listener for change
addlistener(w, 'Changed', @changedFcn);
% Start watching.
w.EnableRaisingEvents = true;
function changedFcn(obj, eData)
   fprintf('Changed: %s\n', char(eData.FullPath));
   ...
end

MATLAB: Automatic import into matlab after time period

You can use a timer for that:

t = timer;
t.Period = 49 * 60;
t.TimerFcn = importfcn; %for you to define with signature: function importfcn(obj, event)
t.ExecutionMode = 'fixedRate';

Alternatively, on Windows, you could use .Net System.IO.FileSystemWatcher to raise an event whenever the file is modified

fsw = System.IO.FileSystemWatcher();
fsw.Path = 'somefolder';
fsw.Filter = 'filename.csv';
fsw.EnableRaisingEvents = true;
listenerhandle = addlistener(fsw, 'Changed', importfcn);
%signature of importfcn is function importfcn(sender, eventargs)
%add a small delay in importfcn before reading the file as the event is raised
%to make sure that file modification is complete

Best Answer

Related Solutions

MATLAB: Errors with polling directory for new files to process

MATLAB: Automatic import into matlab after time period

Related Question