QFileSystemWatcher not updating on file change

Christian Ehrlicher

You need to specify which filesystem watcher backend is used and what filesystem you're working on.
Also a minimal, compilable example is needed.

Aleksey_K

@Christian-Ehrlicher said in QFileSystemWatcher not updating on file change:

You need to specify which filesystem watcher backend is used and what filesystem you're working on.
Also a minimal, compilable example is needed.

etx4. what minimal example? I just connect QFileSystemWatcher::fileChanged to a class slot. And it triggers in UI app when I edit a file in an editor. If if do it in tests:

void write_data(const std::string &content, const std::string &file_Name)
{
    std::ofstream output_file(file_Name, std::ios_base::out | std::ios_base::trunc);
    output_file << content;
    output_file.flush();
}

imitating file change, the signal and therefore my class slot does not trigger for some reason.

Christian Ehrlicher

If you want a solution you should provide the developer a good working base. Creating a simple example and providing essential information to a bug report is therefore a good idea to get your bug fixed. Otherwise it might get closed because it's not reproducible for the developer. But it's up to you - just don't blame us when the bug is closed with 'Needs more info'.

J.Hilk

@Aleksey_K
here,

you're welcome.

#include <QApplication>

#include <ios>
#include <fstream>

#include <QFileSystemWatcher>
#include <QPushButton>
#include <QFile>
#include <QDebug>

void write_data(const std::string &content, const std::string &file_Name)
{
    std::ofstream output_file(file_Name, std::ios_base::out | std::ios_base::trunc);
    output_file << content;
    output_file.flush();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QFile f(QCoreApplication::applicationDirPath() + "/testFile.txt");
    qDebug() << QCoreApplication::applicationDirPath() + "/testFile.txt";
    Q_ASSERT(f.open(QIODevice::WriteOnly));
    f.write("asdasdasdasdas");
    f.close();

    QFileSystemWatcher watcher({QCoreApplication::applicationDirPath()});
    QObject::connect(&watcher, &QFileSystemWatcher::fileChanged, [](const QString &path)->void{qDebug() << "File changed"<< path;});

    QPushButton btn("Modify File");
    QObject::connect(&btn, &QPushButton::clicked, [fileName = QCoreApplication::applicationDirPath() + "/testFile.txt"]()->void{
        write_data("blublbub", fileName.toStdString());
    });
    btn.show();


    return a.exec();
}

Aleksey_K

@Christian-Ehrlicher said in QFileSystemWatcher not updating on file change:

If you want a solution you should provide the developer a good working base. Creating a simple example and providing essential information to a bug report is therefore a good idea to get your bug fixed. Otherwise it might get closed because it's not reproducible for the developer. But it's up to you - just don't blame us when the bug is closed with 'Needs more info'.

No problem:

DataClass.h:

#pragma once

#include <QDebug>
#include <QFileSystemWatcher>

class DataClass : public QObject
{
    Q_OBJECT
public:
    DataClass()
    {
        connect(&m_fileWatcher, &QFileSystemWatcher::fileChanged, //
                this, &DataClass::reloadData);
    }

    void reloadData(QString fileName)
    {
        emit dataLoaded();
        m_fileWatcher.addPath(fileName);
        qDebug() << "Data reloaded!";
    }

signals:
    void dataLoaded();

private:
    QFileSystemWatcher m_fileWatcher;
};

BugReproTest.cpp:

#include "DataClass.h"

#include <gtest/gtest.h>

#include <cstdlib>
#include <fstream>
#include <iostream>

#include <QSignalSpy>
#include <QString>

void write_data(const std::string &content, const std::string &file_Name)
{
    std::ofstream output_file(file_Name, std::ios_base::out | std::ios_base::trunc);
    output_file << content;
    output_file.flush();
}

TEST(BugRepro, fileWatcher)
{
    DataClass data;
    QString fileName = "./test_file";
    write_data("1", fileName.toStdString());

    QSignalSpy dataLoadedSpy(&data, SIGNAL(dataLoaded()));
    ASSERT_NO_THROW(data.reloadData(fileName));
    ASSERT_EQ(dataLoadedSpy.count(), 1);
    dataLoadedSpy.pop_front();

    write_data("2", fileName.toStdString());
    ASSERT_EQ(dataLoadedSpy.count(), 1);
    dataLoadedSpy.pop_front();
}

Aleksey_K

@J-Hilk said in QFileSystemWatcher not updating on file change:

@Aleksey_K
here,
you're welcome.

Thanks a lot! I've also added mine above. Are You able to repro? I'm able to repro with Your example as well! Thanks again!

J.Hilk

@Aleksey_K said in QFileSystemWatcher not updating on file change:

Are You able to repro

I'm,
I also tested QFile, instead of fstream and that also does not trigger QFileSystemWatcher

Aleksey_K

@J-Hilk said in QFileSystemWatcher not updating on file change:

@Aleksey_K said in QFileSystemWatcher not updating on file change:

Are You able to repro

I'm,
I also tested QFile, instead of fstream and that also does not trigger QFileSystemWatcher

Confirm, I also mentioned that.

Aleksey_K

@J-Hilk said in QFileSystemWatcher not updating on file change:

@Aleksey_K said in QFileSystemWatcher not updating on file change:

Are You able to repro

I'm,
I also tested QFile, instead of fstream and that also does not trigger QFileSystemWatcher

You created wrong example - need to monitor the file, not dir. I've modified it and it works:

#include <QApplication>

#include <fstream>
#include <ios>

#include <QDebug>
#include <QFile>
#include <QFileSystemWatcher>
#include <QPushButton>

void write_data(const std::string &content, const std::string &file_Name)
{
    std::ofstream output_file(file_Name, std::ios_base::out | std::ios_base::trunc);
    output_file << content;
    output_file.flush();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QString fileName = QCoreApplication::applicationDirPath() + "/testFile.txt";
    QFile f(fileName);
    qDebug() << fileName;
    Q_ASSERT(f.open(QIODevice::WriteOnly));
    f.write("asdasdasdasdas");
    f.close();

    QFileSystemWatcher watcher({ fileName });
    QObject::connect(
            &watcher, &QFileSystemWatcher::fileChanged,
            [](const QString &path) -> void { qDebug() << "File changed" << path; });

    QPushButton btn("Modify File");
    QObject::connect(&btn, &QPushButton::clicked,
                     [fileName = QCoreApplication::applicationDirPath()
                              + "/testFile.txt"]() -> void {
                         write_data("blublbub", fileName.toStdString());
                     });
    btn.show();

    return a.exec();
}

Mine variant does not!

Aleksey_K

No event loop in my test - that is the problem.

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QFileSystemWatcher not updating on file change