Delphi notification when a file gets updated

Question

My app contains documents in its database. The users can open the documents in which case, the document gets saved to a temporary folder and gets opened on the user's computer.

I'd like to get a notification when one of these temporary files are changed, and offer the user to save the changed document back to the database.

What is the most simple way to do this in Delphi7? (I suppose it requires some shell magic or 3rd party component)

Thanks!

Solution 1

You can either:

1. use the Win32 API SHChangeNotifyRegister function to watch for changes in the temp folder, and then have your callback check if your temporary files are reporting changes.

2. since you know the exact file(s) you are interested in, you can manually monitor them directly for changes to their sizes and timestamps using FindFirstFile in a timer or thread.

Solution 2

You can detect changes in your temporary files (or any file) using the TJvChangeNotify component from the JEDI JVCL collection.

Solution 3

In addition to what RRuz and Remy Lebeau wrote:

Note that TJvChangeNotify in the JvChangeNotify unit makes use of the FindFirstChangeNotification API call; this is the MSDN documentation. Note it is a bit counter-intuitive: see the thread mentioned below on how to use it inside a while loop.

There is also the ReadDirectoryChanges API call, which is not wrapped by the JCL/JVCL, and has MSDN documentation here and there is a Delphi win32 example as well.

This thread explains the differences between the two API calls.

--jeroen

Solution 4

Also take a look at this: http://www.cromis.net/blog/downloads/directory-watch/ and How to monitoring directory for files in Delphi XE?

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Comments

[Steve]

Thanks for the info, gonna check these out as well.

[Steve]

I prefer not to use any JVCL components since I've found them to be kind of buggy. Not to talk about having to install gazilion components just to have the one you actually need...

[Server Overflow]

Please note there is a bug in that library. You need to add Terminate in TDirWatchThread.Execute (after SignalError(ErrorMessage)) - Without this it enters an infinite loop when you delete all files from folder then the folder itself ! Steps to reproduce this bug: create folder, monitor folder, put files in folder, delete ALL files from folder, delete folder, app freezes