File changed in QFileSystemWatcher is never triggered

AkshayFP

I am trying to get QFileSystemWatcher::fileChanged trigger by creating a text file in the added path.

I am using Qt 6.5 on MSVC2019.

Here is an example code:

main.cpp

FileWatchService watcher(&app);
watcher.addPath("C:\\Users\\gollaha\\backup");

filewatchservice.h

class FileWatchService : public QObject
{
    Q_OBJECT
public:
    explicit FileWatchService(QObject *parent = nullptr);
    ~FileWatchService();

    QFileSystemWatcher *_watcher;

    void addPath(const QString &path);

signals:
    void contentChanged(const QString &path, const QString whatChanged);

private slots:
    void directoryChanged(const QString &path);
    void fileChanged(const QString &path);
};

filewatchservice.cpp

FileWatchService::FileWatchService(QObject *parent)
    : QObject{parent}
{
    _watcher = new QFileSystemWatcher(this);

    connect(_watcher, &QFileSystemWatcher::fileChanged, this, &FileWatchService::fileChanged);
    connect(_watcher, &QFileSystemWatcher::directoryChanged, this, &FileWatchService::directoryChanged);
}

FileWatchService::~FileWatchService()
{
    if (_watcher != NULL) {
        delete _watcher;
    }
}

void FileWatchService::addPath(const QString &path)
{
    _watcher->addPath(path);
}

void FileWatchService::directoryChanged(const QString &path)
{
    qDebug() << "directory" << path;
    emit contentChanged(path, "director");
}

void FileWatchService::fileChanged(const QString &path)
{
    qDebug() << "file" << path;

    emit contentChanged(path, "file");
}

fileChanged is never triggered even though I added a text to the path. Any help here is appreciated.

Update

I have also tried this:

main.cpp

QFileSystemWatcher *_watcher = new QFileSystemWatcher(&app);
_watcher->addPath("C:\\Users\\gollaha\\backup");
QObject::connect(_watcher, &QFileSystemWatcher::fileChanged, &app, [](QString file){qDebug() << file;});
QObject::connect(_watcher, &QFileSystemWatcher::directoryChanged, &app, [](QString file){qDebug() << file;});

I am able to trigger directoryChanged but not fileChanged

ChrisW67

@AkshayFP As the docs say, fileChanged() is triggered if path is not a directory. You cannot watch a file that does not exist. If you create or modify a file in a directory that is monitored then directoryChanged() is emitted.

On Linux this looks like:

/tmp/test$ cat main.cpp
#include <QCoreApplication>
#include <QDebug>
#include <QFileSystemWatcher>

int main(int argc, char **argv) {
        QCoreApplication app(argc, argv);

        QFileSystemWatcher w;
        w.addPath("/tmp/test");
        QObject::connect(&w, &QFileSystemWatcher::fileChanged,      &app, [](QString file){qDebug() << "file:" << file;});
        QObject::connect(&w, &QFileSystemWatcher::directoryChanged, &app, [](QString file){qDebug() << "dir: " << file;});

        return app.exec();
}

/tmp/test$ make
make: Nothing to be done for 'first'.

/tmp/test$ ./test &
[1] 4227

/tmp/test$ touch . # modify the directory directly
dir:  "/tmp/test"

/tmp/test$ touch anewfile # new file in the directory
dir:  "/tmp/test"

/tmp/test$ touch main.cpp # an existing file is modified
dir:  "/tmp/test"

/tmp/test$ rm anewfile # delete the file we created
dir:  "/tmp/test"

I imagine that Windows behaviour is the same.

Christian Ehrlicher

addPath() returns a bool to see ifit was successful. Also is backup a directory or a file?
See the documentation.

AkshayFP

@Christian-Ehrlicher it does return true. And backup is a folder name. When I try to add a file to backup folder, only the directoryChanged is detected.

Christian Ehrlicher

@AkshayFP said in File changed in QFileSystemWatcher is never triggered:

When I try to add a file to backup folder, only the directoryChanged is detected.

So it's working as expected.

AkshayFP

@Christian-Ehrlicher Wait, so when does fileChanged triggered? That means every time I add a file or a folder, I need to add the path of it to the watcher?

ChrisW67

@AkshayFP As the docs say, fileChanged() is triggered if path is not a directory. You cannot watch a file that does not exist. If you create or modify a file in a directory that is monitored then directoryChanged() is emitted.

On Linux this looks like:

/tmp/test$ cat main.cpp
#include <QCoreApplication>
#include <QDebug>
#include <QFileSystemWatcher>

int main(int argc, char **argv) {
        QCoreApplication app(argc, argv);

        QFileSystemWatcher w;
        w.addPath("/tmp/test");
        QObject::connect(&w, &QFileSystemWatcher::fileChanged,      &app, [](QString file){qDebug() << "file:" << file;});
        QObject::connect(&w, &QFileSystemWatcher::directoryChanged, &app, [](QString file){qDebug() << "dir: " << file;});

        return app.exec();
}

/tmp/test$ make
make: Nothing to be done for 'first'.

/tmp/test$ ./test &
[1] 4227

/tmp/test$ touch . # modify the directory directly
dir:  "/tmp/test"

/tmp/test$ touch anewfile # new file in the directory
dir:  "/tmp/test"

/tmp/test$ touch main.cpp # an existing file is modified
dir:  "/tmp/test"

/tmp/test$ rm anewfile # delete the file we created
dir:  "/tmp/test"

I imagine that Windows behaviour is the same.