QT5 - Detecting when new files are added to a directory and retrieving their path-CodePudding

My problem is relatively simple. I have an application where I need to monitor a particular folder (the downloads folder, in my case) for added files. Whenever a file is added to that folder, I want to move that file to a completely different directory. I have been looking at QFileSystemWatcher; however, none of the signals it provides seems to be ideal for my situation.

Here is my current code:

connect(&m_fileWatcher, &QFileSystemWatcher::directoryChanged, this, &FileHandler::directoryChanged);

void FileHandler::directoryChanged(const QString &dir)
{
  qDebug() << "File changed...." << string;
  // Some other logic
}

This signal only gives me a string to work with which is the directory that witnessed a change. I don't know what kind of change took place (add, rename, or delete), and I also have no idea which file has changed.

I understand that I could store all of the files in the directory in some sort of data structure and do some other logic when this signal is emitted, but that doesn't seem very performant in this case since I'm dealing with the user's downloads folder (which could contain thousands of files).

How can I make this work? Should I refer to a different helper class provided by QT, or is there some other way I can do this while utilizing QFileSystemWatcher? I'm simply just looking for ideas.

Thank you.

CodePudding user response：

You’ve hit the limit of what the underlying OS provides: notification of change to the content of a directory.

If you wish to identify the file:

deleted you must have a prior list of files available for compare
added same as deleted
modified loop through the directory for the file with the most recent last modified date

IDK if you wish to use any specific filename container class from Qt or just a std::vector <std::filesystem::path> or the like for your cached folder contents.

CodePudding user response：

QFileSystemWatcher only notifies you that a change happened, but not the details of what was changed. So you will have to resort to OS-specific APIs to get the details. For instance, on Windows, you can use ReadDirectoryChangesW() instead of QFileSystemWatcher.