Using AppDesigner with FileSystemWatcher

Question

Darrell 2020-6-29

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/556276-using-appdesigner-with-filesystemwatcher

回答： Geoff Hayes 2020-6-30

I am trying to create a MATLAB app that uses FileSystemWatcher to call an event handler each time a specific file has changed--using version 2018b. I have created the following two functions in Code View using the appdesigner; however the app never calls 'eventhandlerChanged' function. I've spent a lot of time trying to get this to work, so any help would be greatly appreciated.

 % Button pushed function: TestFSWButton
        function AddFSW(app, event)
            fileObj = System.IO.FileSystemWatcher('D:\Matlab\Work');
	    fileObj.Filter = 'test.csv';
	    fileObj.EnableRaisingEvents = true;
            addlistener(fileObj,'Changed',@app.eventhandlerChanged);
        end        
        
        function eventhandlerChanged(app,evt)
            tic;
            toc;    
        end   

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Darrell 2020-6-29

在 MATLAB Online 中打开

Geoff,

That worked! Below is the final code.

properties (Access = private)
    myFSW           % FileSystemWatcher object
end
function eventhandlerChanged(app,~,~)
    % do stuff
    disp('Successful!');
end 
% Button pushed function: TestButton
function AddFSW(app, event)
    app.myFSW = System.IO.FileSystemWatcher('D:\Matlab\Work');
    app.myFSW.Filter = 'test.csv';
    app.myFSW.EnableRaisingEvents = true;
    addlistener(app.myFSW,'Changed',@app.eventhandlerChanged);
end

Note. If you modify the test file using Notepad the method will fire twice; but if you are watching for an actual file it all works correctly. Thank you!

Geoff Hayes 2020-6-30

Glad it worked out! :)

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Answer 1

Geoff Hayes 2020-6-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/556276-using-appdesigner-with-filesystemwatcher#answer_458806

Summary of issue: from Create event listener bound to event source it shows that the call to addlistener returns an object. In the above code, this object is local to the AddFSW method and so would be destroyed when the method "completes" which would mean that we no longer have an object listening for changes to the file. The fix is to make the listener object a member of the app so that it exists for the lifetime of the app (or until removed or deleted if needed).