There any way to trigger an action if a file in a specified directory ( or in a subfolder ) without fetching all modification times every time ? I'm asking because i've to check this live
You need to use the QFileSystemWatcher.
More importantly, this is the signal you need to connect to:
void QFileSystemWatcher::fileChanged(const QString & path) [signal]
This signal is emitted when the file at the specified path is modified, renamed or removed from disk.
See also directoryChanged().
So, you could write something like this in your class or function:
...
QFileSystemWatcher watcher;
watcher.addPath("/My/Path/To/The/File");
QObject::connect(&watcher, SIGNAL(fileChanged(const QString&)), receiver, SLOT(handleFileChanged(const QString&)));
...
You're looking for QFileSystemWatcher.
Related
I am trying to watch the changes in a directory using QFileSystemModel. Whenever I rename a file in the root path, only the directoryLoaded() signal is emitted. I want the fileRenamed() signal to be emitted so that I know which file is renamed to a new name. Here is my code:
model = new QFileSystemModel;
model->setRootPath("C:/test/");
QObject::connect(model, SIGNAL(fileRenamed(const QString&, const QString&, const QString&)), this, SLOT(updateRename()));
QObject::connect(model, SIGNAL(directoryLoaded(const QString&)), this, SLOT(loadDir()));
I am afraid you expect too much from this QFileSystemModel class. It does not and cannot catch if the renaming operation happens outside of the model. I looked up all uses of fileRenamed() signal and it seems that the only place where it is emitted is here: https://code.woboq.org/qt5/qtbase/src/widgets/dialogs/qfilesystemmodel.cpp.html#933
And if you go a few lines above, you can see that this is triggered when the renaming happens inside this function https://code.woboq.org/qt5/qtbase/src/widgets/dialogs/qfilesystemmodel.cpp.html#873 In other words, if you use QFileSystemModel::setData() to set a name to an item, it will rename the item and emit the signal. And it is the only way to have the signal emitted.
And this is logical, if renaming happens outside of your program, then there is no certain way to find out that a certain file was renamed. Your application only observes that some file disappeared and another file with a different name emerged. Of course, you can check whether the timestamp and size of the file is the same, whether they are also in the same parent folder, maybe also check the file content... and only if these things match and the only difference is in the file names, then you can conclude that the file was renamed. But this is something you must program yourself. QFileSystemModel will not do it for you because it does not know your specific intentions.
QFileSystemWatcher watcher;
watcher.addPath("C:/watch");
QStringList directoryList = watcher.directories();
Q_FOREACH(QString directory, directoryList)
qDebug() << "Directory name" << directory <<"\n";
DirectoryWatcher* dw = new DirectoryWatcher;
QObject::connect(
&watcher, SIGNAL(directoryChanged(const QString&)),
dw, SLOT(modified(const QString&))
);
QObject::connect(
&watcher, SIGNAL(fileChanged(QString)),
dw, SLOT(modified(QString))
);
In this sample, modified() method called when;
a new file created
a file deleted
a file renamed
But, If i open a file in this folder and modify the content, after I save it, nothing called.
IF I add that specific file to the path like addPath("c:/watch/me.txt") then after modify it gets invoked.
But as you might know, there is a limitation on watcher. So I cannot watch hundreds of files every time.
How can I invoke modified() method on file modifications?
If you want a cross-platform solution, using Qt5::QFileSystemWatcher, you have no other way than adding each files from the directory you're watching to the QFileSystemWatcher object, hoping that you don't hit the file descriptors limitation.
If you want to use OS specific methods to watch filesystem, you can get some hints from this S/O answer : https://stackoverflow.com/a/931165/228634 but I'm pretty sure you'll have the same limitations.
I need to update the content of a field on my QWidget via a JSON file (updated in real time). I've read about functions readLine() and readAll() of QFile, but when I try a loop like :
while(true):
jsfile.readLine()
creation of objects, update of values, display etc ...
I lost the focus on my window. But I want to keep the control of the application with my buttons and obviously to watch the evolution of the JSON values.
I have thought that Qt manages itself the events and keeps the focus on the current window, but like I've said, it's not the case.
Is there a good solution (multi threads maybe) to use my window while the application reads the file (with new informations in real time)?
(With the constraint "real time" I can't read the whole file every time and I've no choice about the format of this file)
Update
I tried the thread method.
So, I choose to create my thread instance into the main (with my main window) and connect here. But, when I run the program, I've this error :
no matching member function for call to 'connect'
Reader reader;
QObject::connect(controler, SIGNAL(ready()),
reader, SLOT(received()));
According to this error, I've thought that the reason was main don't inherits of Object, and so, I've move the connection ans the creation of thread instance into my main window.
Reader reader;
QObject::connect(reader, SIGNAL(newobject(QJsonObject)),
this, SLOT(displayJSON(QJsonObject)));
With this one, I've the same error while I've already connect lot of widget into this class without any error.
What can be the problem ?
Update 2
I've a solution when I give as argument my main window (controler) in reader's constructor and connect into this one but, if possible, I would an explanation for the previous problem.
The current problem that I have is that signals are emit well but slots are executed after the end the application (so after the end of the thread's execution and not during)
This isn't really the subject of this topic so we can close this one.
You can use QThread (Qt documentation: QThread) class to create a thread, which will read your file. The main thread will execute your GUI application and it will be available during file reading.
You can find a simple example in documentation for creating your thread:
class WorkerThread : public QThread
{
Q_OBJECT
void run() Q_DECL_OVERRIDE {
QString result;
/* ... here is the expensive or blocking operation ... */
emit resultReady(result);
}
signals:
void resultReady(const QString &s);
};
void MyObject::startWorkInAThread()
{
WorkerThread *workerThread = new WorkerThread(this);
connect(workerThread, &WorkerThread::resultReady, this, &MyObject::handleResults);
connect(workerThread, &WorkerThread::finished, workerThread, &QObject::deleteLater);
workerThread->start();
}
You can modify this example for your purpose. For example, WorkerThread for your task may be something like this:
class WorkerThread : public QThread
{
Q_OBJECT
void run() Q_DECL_OVERRIDE {
while(!stopFlag)
{
// read JSON file to QByteArray. Use QFile and QTextStream
// use QJsonDocument to read JSON content
// find what is new in JSON
emit signalSomethingNew(/*parameters*/);
QThread::currentThread()->msleep(/*timeout*/);
}
}
signals:
void signalSomethingNew(/*parameters*/);
};
At the end you must implement slot on your QWidget for signalSomethingNew(/*parameters*/) and make connection:
connect(yourThread, &WorkingThread::signalSomethingNew, youWidget, &YouWidget::yourSlot);
For working with JSON data: QJsonDocument
I'm interpreting your question as "my application is unresponsive whilst doing work" rather than "my focus jumped to another window" - please comment if you meant something different.
You have a choice of options:
Create and run a background QThread to do the work. Have it emit signals (connected to your widgets using Qt::QueuedConnection - the default) when it has results to display.
This is a good solution when the worker has a lot of computation to do, or needs all the input to be read before it can start. It works very well when the target system has processors available with no other work to do.
Use a QSocketNotifier to signal your GUI thread when some of the input becomes available (note that the name is misleading - it actually works on all kinds of file descriptor, not just sockets).
This is appropriate when the algorithm is simple and incremental - i.e. if a small chunk of input can be read and processed quickly.
Incorporate periodic calls to processEvents() in your algorithm:
auto *const dispatcher = QThread::currentThread()->eventDispatcher;
while (line = json.readLine()) {
doSomethingWith(line);
if (dispatcher)
dispatcher->processEvents();
}
This won't work unless you can modify the algorithm like this - if the loop is in somebody else's (closed) code, then you'll need one of the other solutions.
I have a C++ plugin that watches for file changes with QFileSystemWatcher and connects it's fileChanged signal with a custom QML type slot like this:
//In the custom QML type constructor
QObject::connect(&this->_watcher, SIGNAL(fileChanged(QString)),
this, SLOT(fileChangedSlot(QString)));
The slot function:
void CustomQMLTypeClass::fileChangedSlot(QString file)
{
Q_UNUSED(file);
emit fileChanged();
}
In the QML side:
CustomQMLType{
fileUri: "some/file/path/file.format"
onFileChanged: console.log("File changed")
}
While running the program all goes right, but when I do, i.e.:
echo "sth" >> some/file/path/file.format
More than once, the notification is only triggered once. Why? O.o
Apparently the problem is with QFileSystemWatcher, it sometimes worked and some others don't.
As I can handle the cost, my quick solution was to alter the slot:
void CustomQMLTypeClass::fileChangedSlot(QString &file)
{
_watcher.removePath(file);
_watcher.addPath(file);
emit fileChanged();
}
Now it works as expected but don't know why and couldn't get to understand neither with QFileSystemWatcher's source. Finally I decided KDE's KDirWatch is way better.
Whenever I select a file in my QFileDialog the accepted signal is fired and the window closes. I want to keep the window open so I can select multiple files and then capture the signal fired when "open" is clicked.
QFileDialog* myDialog = new QFileDialog(this);
myDialog->setFileMode(QFileDialog::ExistingFiles);
myDialog->setVisible(true);
What signals should I be connecting here to achieve this effect?
The QFileDialog::ExistingFiles should guarantee that multiple files can be selected. Given that, you can connect to the signal:
void QFileDialog::filesSelected(const QStringList & selected)
Directly from the documentation:
When the selection changes for local operations and the dialog is accepted, this signal is emitted with the (possibly empty) list of selected files.
However, if you are only interested in collecting such files, you can totally avoid signal-slot and write (taken again from the documentation):
QStringList fileNames;
if (dialog.exec())
fileNames = dialog.selectedFiles();
Note that in this case dialog object has been created on the stack (which is the common approach for such objects).
Your code looks fine to me. I believe you are double clicking on the file inside the dialog instead of holding on the Ctrl and single clicking on all the files you need.
You can optionally use an event filter and ignore the double click event.
Once you click on Open, you can get a list of all the file paths in the QStringList given by QFileDialog::selectedFiles(). Also it's better to use a stack variable here and use exec method to launch it as pointed out by BaCaRoZzo.
QFileDialog myDialog(this);
myDialog.setFileMode(QFileDialog::ExistingFiles);
if(myDialog.exec())
{
qDebug() << myDialog.selectedFiles();
}
Whenever I select a file in my QFileDialog the accepted signal is fired and the window closes. I want to keep the window open so I can select multiple files
All other answers is just solution for selection many files one time and CLOSE window after Open button pressing. Get my solution, it is not very simple because it required lot of work:
I used lamda expressions and new signals and slots syntax in my answer, but you can use old syntax or add
CONFIG += c++11
to the .pro file and use lambdas.
Subclass QFileDialog:
Header:
#ifndef CUSTOMFILEDIALOG_H
#define CUSTOMFILEDIALOG_H
#include <QFileDialog>
#include <QDebug>
class CustomFileDialog : public QFileDialog
{
Q_OBJECT
public:
explicit CustomFileDialog(QWidget *parent = 0);
void setDefaultGeo(QRect);
signals:
void newPathAvailable(QStringList list);
public slots:
private:
bool openClicked;
QRect geo;
};
#endif // CUSTOMFILEDIALOG_H
When you click open, you hide your dialog, not close! Cpp:
#include "customfiledialog.h"
CustomFileDialog::CustomFileDialog(QWidget *parent) :
QFileDialog(parent)
{
openClicked = false;
connect(this,&QFileDialog::accepted,[=]() {
openClicked = true;
qDebug() << openClicked;
this->setGeometry(geo);
this->show();
emit newPathAvailable(this->selectedFiles());
});
}
void CustomFileDialog::setDefaultGeo(QRect rect)
{
geo = rect;
}
Usage:
CustomFileDialog *dialog = new CustomFileDialog;
QStringList fileNames;
dialog->setFileMode(QFileDialog::ExistingFiles);
dialog->show();
dialog->setDefaultGeo(dialog->geometry());
connect(dialog,&CustomFileDialog::newPathAvailable,[=](QStringList path) {
qDebug() << path;
});
Why do you need setDefaultGeo? Without this method, your window will move after Open pressing.
What we get?
I open filedialog and select two files:
I clicked Open, but window didn't close! You can choose new files again and again!
One more file and so on:
Window will closed only when user press Close button, but you will have all path which user choose.
As you said:
I want to keep the window open so I can select multiple files
You get this.
I don't think anyone has understood the question (or it could be just me looking for my own solution)...
I had the same issue. As soon as I clicked a file the dialog would close. I couldn't ever select a file and then click "Open" because the dialog instantly closed as soon as I single clicked a file.
related: qtcentre.org/threads/48782-QFileDialog-single-click-only
It turns out it was my linux os settings (under mouse). File opening was set to single-click. I still feel like something external might have toggled this but that is just speculation. It appears Qt was going the right thing. Check another application, like kate on KDE and see if it has the same behavior. That is what clued me in to the source of my issue.