Using .NET FileSystemWatcher to listen for new files

Hi,

I want to write a simple program that runs continuously and listens for the FileSystemWatcher events i.e. a new file has appeared in a folder. When the file arrives I want to process that file in some way. The following is code that I have been playing with:

function ImageSorter
%Start listeners for file new notifications
   fileObj = System.IO.FileSystemWatcher('C:\Dicom\');
   fileObj.EnableRaisingEvents = true;
   l1 = addlistener(fileObj, 'Created', @eventhandlerChanged);

%now I want the program to stop and listen for the events and not 
% continue to the end.
   h = figure('visible','off');
   waitfor(h);
   delete(l1);
end

function eventhandlerChanged(source,arg)
    arg.FullPath
end

If I insert a break point at the end of the ImageSorter program then it works and the eventhandlerChanged function is called when a new file appears in the folder C:\DICOM.

How do I make the function stop running to the end and wait for the listening events?

Jonathan

[Ashish Uthama]

how about putting in a 'pause'?

Answer 1

[Matthew Whitaker]

Jonathon, Here is an example of how to do it. Note you need to listen on the changed event and not the created event

function FileWatch(pathToWatch)
txtDetectedFiles = createFigure;
fileObj = System.IO.FileSystemWatcher(pathToWatch);
fileObj.EnableRaisingEvents = true;
changeListener =addlistener(fileObj, 'Changed', @onChange); %need to keep in scope

    function txtDetectedFiles = createFigure
        figHdl = figure('Name','FileWatcher',...
                              'Menubar','none',...
                              'Toolbar','none',...
                              'NumberTitle','off',...
                              'Units','normalized',...
                              'Position',[0.4,0.4,0.4,0.2]);

        uicontrol('Parent',figHdl,...
                     'Style','text',...
                     'Units','normalized',...
                     'Position',[0.1,0.9,0.8,0.08],...
                     'String',['Path Watched: ',pathToWatch]);

        uicontrol('Parent',figHdl,...
                      'Style','pushbutton',...
                      'String','Write a file to the watched path.',...
                      'Units','normalized',...
                      'Position',[0.1,0.6,0.5,0.2],...
                      'Callback',@cmdWriteFile);
        txtDetectedFiles = uicontrol('Parent',figHdl,...
                                                 'Style','edit',...
                                                 'Enable','inactive',...
                                                 'Units','normalized',...
                                                 'Position',[0.1,0.05,0.8,0.45],...
                                                 'Max',3);

    end %createFigure

    function cmdWriteFile(varargin)
        %create a simple text file in the watched folder
        tName = tempname;
        [~,tName] = fileparts(tName);
        fName =fullfile(pathToWatch,[tName,'.txt']);
        dlmwrite(fName,1:5);
    end %cmdWriteFile

    function onChange(~,evt)
        existStr = get(txtDetectedFiles,'String');
        if isempty(existStr)
            existStr = {};
        end %if

        existStr{length(existStr)+1} = ['New file Detected: ',char(evt.FullPath.ToString())];
        set(txtDetectedFiles,'String',existStr);
    end %onChange
end %FileWatch

[Jonathan Sykes]

I'd been struggling with that for too many hours and so your answer (which works really well) was very welcome. Many thanks!

[Matthew Whitaker]

Great , glad it helped! Can you set that you accept the answer?

Thanks

Matt

[Jagatpreet]

Your example was of great help. It provides me the answer to my two questions:

How can GUI be used while listening events

How to watch file system and send notification when new file is added programmatically.

Previously I was watching the file using timer function Thanks a lot

Answer 2

[E]

Hi , Im trying to use this piece of code but i have no need in the button that creates new files so i commented the following lines:

uicontrol('Parent',figHdl,...
                    'Style','pushbutton',...
                    'String','Write a file to the watched path.',...
                    'Units','normalized',...
                    'Position',[0.1,0.6,0.5,0.2],...
                    'Callback',@cmdWriteFile);

and its corresponding callback:

 function cmdWriteFile(varargin)
        %create a simple text file in the watched folder
        tName = tempname;
        [~,tName] = fileparts(tName);
        fName =fullfile(pathToWatch,[tName,'.txt']);
        dlmwrite(fName,1:5);
    end %cmdWriteFile

After doing so, the listener is not listening and onCahnge() is not running on change...

any ides how are my actions related to the listener?

Thanks!

[Mr.Dong]

I have the same problem，so how you deal with it?