\inmodule QtCore More...

#include <qfilesystemwatcher.h>

Inheritance diagram for QFileSystemWatcher:

Collaboration diagram for QFileSystemWatcher:

Signals
void	fileChanged (const QString &path, QPrivateSignal)
	This signal is emitted when the file at the specified path is modified, renamed or removed from disk.

void	directoryChanged (const QString &path, QPrivateSignal)
	This signal is emitted when the directory at a specified path is modified (e.g., when a file is added or deleted) or removed from disk.

Signals inherited from QObject
void	destroyed (QObject *=nullptr)
	This signal is emitted immediately before the object obj is destroyed, after any instances of QPointer have been notified, and cannot be blocked.

void	objectNameChanged (const QString &objectName, QPrivateSignal)
	This signal is emitted after the object's name has been changed.

Public Member Functions
	QFileSystemWatcher (QObject *parent=nullptr)
	Constructs a new file system watcher object with the given parent.

	QFileSystemWatcher (const QStringList &paths, QObject *parent=nullptr)
	Constructs a new file system watcher object with the given parent which monitors the specified paths list.

	~QFileSystemWatcher ()
	Destroys the file system watcher.

bool	addPath (const QString &file)
	Adds path to the file system watcher if path exists.

QStringList	addPaths (const QStringList &files)
	Adds each path in paths to the file system watcher.

bool	removePath (const QString &file)
	Removes the specified path from the file system watcher.

QStringList	removePaths (const QStringList &files)
	Removes the specified paths from the file system watcher.

QStringList	files () const
	Returns a list of paths to files that are being watched.

QStringList	directories () const
	Returns a list of paths to directories that are being watched.

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)
	Constructs an object with parent object parent.

virtual	~QObject ()
	Destroys the object, deleting all its child objects.

virtual bool	event (QEvent *event)
	This virtual function receives events to an object and should return true if the event e was recognized and processed.

virtual bool	eventFilter (QObject watched, QEvent event)
	Filters events if this object has been installed as an event filter for the watched object.

QString	objectName () const

Q_WEAK_OVERLOAD void	setObjectName (const QString &name)
	Sets the object's name to name.

void	setObjectName (QAnyStringView name)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const
	Returns `true` if the object is a widget; otherwise returns `false`.

bool	isWindowType () const
	Returns `true` if the object is a window; otherwise returns `false`.

bool	isQuickItemType () const
	Returns `true` if the object is a QQuickItem; otherwise returns `false`.

bool	signalsBlocked () const noexcept
	Returns `true` if signals are blocked; otherwise returns `false`.

bool	blockSignals (bool b) noexcept
	If block is true, signals emitted by this object are blocked (i.e., emitting a signal will not invoke anything connected to it).

QThread *	thread () const
	Returns the thread in which the object lives.

bool	moveToThread (QThread *thread QT6_DECL_NEW_OVERLOAD_TAIL)
	Changes the thread affinity for this object and its children and returns `true` on success.

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
	This is an overloaded function that will start a timer of type timerType and a timeout of interval milliseconds.

int	startTimer (std::chrono::nanoseconds time, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)
	Kills the timer with timer identifier, id.

void	killTimer (Qt::TimerId id)

template<typename T >
T	findChild (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns the child of this object that can be cast into type T and that is called name, or \nullptr if there is no such object.

template<typename T >
QList< T >	findChildren (QAnyStringView aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	Returns all children of this object with the given name that can be cast to type T, or an empty list if there are no such objects.

template<typename T >
T	findChild (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

const QObjectList &	children () const
	Returns a list of child objects.

void	setParent (QObject *parent)
	Makes the object a child of parent.

void	installEventFilter (QObject *filterObj)
	Installs an event filter filterObj on this object.

void	removeEventFilter (QObject *obj)
	Removes an event filter object obj from this object.

QMetaObject::Connection	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=nullptr, const QObject receiver=nullptr, const char *member=nullptr) const

bool	disconnect (const QObject receiver, const char member=nullptr) const

void	dumpObjectTree () const
	Dumps a tree of children to the debug output.

void	dumpObjectInfo () const
	Dumps information about signal connections, etc.

bool	setProperty (const char *name, const QVariant &value)
	Sets the value of the object's name property to value.

bool	setProperty (const char *name, QVariant &&value)

QVariant	property (const char *name) const
	Returns the value of the object's name property.

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const
	Returns a pointer to the parent object.

bool	inherits (const char *classname) const
	Returns `true` if this object is an instance of a class that inherits className or a QObject subclass that inherits className; otherwise returns `false`.

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)
	\threadsafe

static QMetaObject::Connection	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::ContextTypeForFunctor< Func2 >::ContextType context, Func2 &&slot, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 &&slot)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)
	\threadsafe

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static bool	disconnect (const QMetaObject::Connection &)
	Disconnect a connection.

template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot)

template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject receiver, void **zero)

Protected Member Functions inherited from QObject
QObject *	sender () const
	Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns \nullptr.

int	senderSignalIndex () const

int	receivers (const char *signal) const
	Returns the number of receivers connected to the signal.

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)
	This event handler can be reimplemented in a subclass to receive timer events for the object.

virtual void	childEvent (QChildEvent *event)
	This event handler can be reimplemented in a subclass to receive child events.

virtual void	customEvent (QEvent *event)
	This event handler can be reimplemented in a subclass to receive custom events.

virtual void	connectNotify (const QMetaMethod &signal)

virtual void	disconnectNotify (const QMetaMethod &signal)

	QObject (QObjectPrivate &dd, QObject *parent=nullptr)

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Properties inherited from QObject
QString	objectName
	the name of this object

Related Symbols inherited from QObject
template< class T > T	qobject_cast (const QObject *object)
	Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList
	\macro Q_CLASSINFO(Name, Value)

Detailed Description

\inmodule QtCore

The QFileSystemWatcher class provides an interface for monitoring files and directories for modifications.

Since: 4.2 \reentrant

QFileSystemWatcher monitors the file system for changes to files and directories by watching a list of specified paths.

Call addPath() to watch a particular file or directory. Multiple paths can be added using the addPaths() function. Existing paths can be removed by using the removePath() and removePaths() functions.

QFileSystemWatcher examines each path added to it. Files that have been added to the QFileSystemWatcher can be accessed using the files() function, and directories using the directories() function.

The fileChanged() signal is emitted when a file has been modified, renamed or removed from disk. Similarly, the directoryChanged() signal is emitted when a directory or its contents is modified or removed. Note that QFileSystemWatcher stops monitoring files once they have been renamed or removed from disk, and directories once they have been removed from disk.

\list

Notes: \list
On systems running a Linux kernel without inotify support, file systems that contain watched paths cannot be unmounted.

The act of monitoring files and directories for modifications consumes system resources. This implies there is a limit to the number of files and directories your process can monitor simultaneously. On all BSD variants, for example, an open file descriptor is required for each monitored file. Some system limits the number of open file descriptors to 256 by default. This means that addPath() and addPaths() will fail if your process tries to add more than 256 files or directories to the file system monitor. Also note that your process may have other file descriptors open in addition to the ones for files being monitored, and these other open descriptors also count in the total. \macos uses a different backend and does not suffer from this issue. \endlist \endlist

See also: QFile, QDir

Definition at line 16 of file qfilesystemwatcher.h.

Constructor & Destructor Documentation

◆ QFileSystemWatcher() [1/2]

QFileSystemWatcher::QFileSystemWatcher ( QObject * parent = nullptr )

Constructs a new file system watcher object with the given parent.

Definition at line 220 of file qfilesystemwatcher.cpp.

◆ QFileSystemWatcher() [2/2]

QFileSystemWatcher::QFileSystemWatcher	(	const QStringList &	paths,
		QObject *	parent = nullptr )

Constructs a new file system watcher object with the given parent which monitors the specified paths list.

Definition at line 230 of file qfilesystemwatcher.cpp.

References addPaths().

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◆ ~QFileSystemWatcher()

QFileSystemWatcher::~QFileSystemWatcher ( )

Destroys the file system watcher.

Definition at line 240 of file qfilesystemwatcher.cpp.

Member Function Documentation

◆ addPath()

bool QFileSystemWatcher::addPath ( const QString & path )

Adds path to the file system watcher if path exists.

The path is not added if it does not exist, or if it is already being monitored by the file system watcher.

If path specifies a directory, the directoryChanged() signal will be emitted when path is modified or removed from disk; otherwise the fileChanged() signal is emitted when path is modified, renamed or removed.

If the watch was successful, true is returned.

Reasons for a watch failure are generally system-dependent, but may include the resource not existing, access failures, or the total watch count limit, if the platform has one.

Note: There may be a system dependent limit to the number of files and directories that can be monitored simultaneously. If this limit is been reached, path will not be monitored, and false is returned.

See also: addPaths(), removePath()

Definition at line 266 of file qfilesystemwatcher.cpp.

References addPaths(), and qWarning.

Referenced by QV4L2CameraDevices::QV4L2CameraDevices().

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◆ addPaths()

QStringList QFileSystemWatcher::addPaths ( const QStringList & paths )

Adds each path in paths to the file system watcher.

Paths are not added if they not exist, or if they are already being monitored by the file system watcher.

If a path specifies a directory, the directoryChanged() signal will be emitted when the path is modified or removed from disk; otherwise the fileChanged() signal is emitted when the path is modified, renamed, or removed.

The return value is a list of paths that could not be watched.

Reasons for a watch failure are generally system-dependent, but may include the resource not existing, access failures, or the total watch count limit, if the platform has one.

Note: There may be a system dependent limit to the number of files and directories that can be monitored simultaneously. If this limit has been reached, the excess paths will not be monitored, and they will be added to the returned QStringList.

See also: addPath(), removePaths()

Definition at line 311 of file qfilesystemwatcher.cpp.

References d, empty_paths_pruned(), engine, QString::mid(), QObject::objectName, Q_UNLIKELY, qCDebug, qWarning, and QString::startsWith().

Referenced by QFileSystemWatcher(), and addPath().

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◆ directories()

QStringList QFileSystemWatcher::directories ( ) const

Returns a list of paths to directories that are being watched.

See also: files()

Definition at line 451 of file qfilesystemwatcher.cpp.

References d.

◆ directoryChanged

void QFileSystemWatcher::directoryChanged	(	const QString &	path,
		QPrivateSignal	)

signal

This signal is emitted when the directory at a specified path is modified (e.g., when a file is added or deleted) or removed from disk.

Note that if there are several changes during a short period of time, some of the changes might not emit this signal. However, the last change in the sequence of changes will always generate this signal.

See also: fileChanged()

Referenced by QV4L2CameraDevices::QV4L2CameraDevices().

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◆ fileChanged

void QFileSystemWatcher::fileChanged	(	const QString &	path,
		QPrivateSignal	)

signal

This signal is emitted when the file at the specified path is modified, renamed or removed from disk.

Note: As a safety measure, many applications save an open file by writing a new file and then deleting the old one. In your slot function, you can check watcher.files().contains(path). If it returns false, check whether the file still exists and then call addPath() to continue watching it.