The QNetworkDiskCache class provides a very basic disk cache. More...

#include <qnetworkdiskcache.h>

Inheritance diagram for QNetworkDiskCache:

Collaboration diagram for QNetworkDiskCache:

Public Slots
void	clear () override
	\reimp

Public Slots inherited from QAbstractNetworkCache
virtual void	clear ()=0
	Removes all items from the cache.

Public Slots inherited from QObject
void	deleteLater ()
	\threadsafe

Public Member Functions
	QNetworkDiskCache (QObject *parent=nullptr)
	Creates a new disk cache.

	~QNetworkDiskCache ()
	Destroys the cache object.

QString	cacheDirectory () const
	Returns the location where cached files will be stored.

void	setCacheDirectory (const QString &cacheDir)
	Sets the directory where cached files will be stored to cacheDir.

qint64	maximumCacheSize () const
	Returns the current maximum size for the disk cache.

void	setMaximumCacheSize (qint64 size)
	Sets the maximum size of the disk cache to be size.

qint64	cacheSize () const override
	\reimp

QNetworkCacheMetaData	metaData (const QUrl &url) override
	\reimp

void	updateMetaData (const QNetworkCacheMetaData &metaData) override
	\reimp

QIODevice *	data (const QUrl &url) override
	\reimp

bool	remove (const QUrl &url) override
	\reimp

QIODevice *	prepare (const QNetworkCacheMetaData &metaData) override
	\reimp

void	insert (QIODevice *device) override
	\reimp

QNetworkCacheMetaData	fileMetaData (const QString &fileName) const
	Returns the QNetworkCacheMetaData for the cache file fileName.

Public Member Functions inherited from QAbstractNetworkCache
virtual	~QAbstractNetworkCache ()
	Destroys the cache.

virtual QNetworkCacheMetaData	metaData (const QUrl &url)=0
	Returns the meta data for the url url.

virtual void	updateMetaData (const QNetworkCacheMetaData &metaData)=0
	Updates the cache meta date for the metaData's url to metaData.

virtual QIODevice *	data (const QUrl &url)=0
	Returns the data associated with url.

virtual bool	remove (const QUrl &url)=0
	Removes the cache entry for url, returning true if success otherwise false.

virtual qint64	cacheSize () const =0
	Returns the current size taken up by the cache.

virtual QIODevice *	prepare (const QNetworkCacheMetaData &metaData)=0
	Returns the device that should be populated with the data for the cache item metaData.

virtual void	insert (QIODevice *device)=0
	Inserts the data in device and the prepared meta data into the cache.

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.

void	moveToThread (QThread *thread)
	Changes the thread affinity for this object and its children.

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::milliseconds time, Qt::TimerType timerType=Qt::CoarseTimer)

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

template<typename T >
T	findChild (const QString &aName=QString(), 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 (const QString &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 >
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`.

Protected Member Functions
virtual qint64	expire ()
	Cleans the cache so that its size is under the maximum cache size.

Protected Member Functions inherited from QAbstractNetworkCache
	QAbstractNetworkCache (QObject *parent=nullptr)
	Constructs an abstract network cache with the given parent.

	QAbstractNetworkCache (QAbstractNetworkCachePrivate &dd, QObject *parent)

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)

Additional Inherited Members
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.

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 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

The QNetworkDiskCache class provides a very basic disk cache.

Since: 4.5 \inmodule QtNetwork

QNetworkDiskCache stores each url in its own file inside of the cacheDirectory using QDataStream. Files with a text MimeType are compressed using qCompress. Data is written to disk only in insert() and updateMetaData().

Currently you cannot share the same cache files with more than one disk cache.

QNetworkDiskCache by default limits the amount of space that the cache will use on the system to 50MB.

Note you have to set the cache directory before it will work.

A network disk cache can be enabled by:

QNetworkAccessManager *manager = new QNetworkAccessManager(this);
QNetworkDiskCache *diskCache = new QNetworkDiskCache(this);
QString directory = QStandardPaths::writableLocation(QStandardPaths::CacheLocation)
        + QLatin1StringView("/cacheDir/");
diskCache->setCacheDirectory(directory);
manager->setCache(diskCache);

When sending requests, to control the preference of when to use the cache and when to use the network, consider the following:

using namespace Qt::StringLiterals;
// do a normal request (preferred from network, as this is the default)
QNetworkRequest request(QUrl(u"http://qt-project.org"_s));
manager->get(request);
 
// do a request preferred from cache
QNetworkRequest request2(QUrl(u"http://qt-project.org"_s));
request2.setAttribute(QNetworkRequest::CacheLoadControlAttribute, QNetworkRequest::PreferCache);
manager->get(request2);

To check whether the response came from the cache or from the network, the following can be applied:

void replyFinished(QNetworkReply *reply) {
    QVariant fromCache = reply->attribute(QNetworkRequest::SourceIsFromCacheAttribute);
    qDebug() << "page from cache?" << fromCache.toBool();
}

Definition at line 15 of file qnetworkdiskcache.h.

Constructor & Destructor Documentation

◆ QNetworkDiskCache()

QNetworkDiskCache::QNetworkDiskCache ( QObject * parent = nullptr )

explicit

Creates a new disk cache.

The parent argument is passed to QAbstractNetworkCache's constructor.

Definition at line 71 of file qnetworkdiskcache.cpp.

◆ ~QNetworkDiskCache()

QNetworkDiskCache::~QNetworkDiskCache ( )

Destroys the cache object.

This does not clear the disk cache.

Definition at line 79 of file qnetworkdiskcache.cpp.

References d, and qDeleteAll().

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Member Function Documentation

◆ cacheDirectory()

QString QNetworkDiskCache::cacheDirectory ( ) const

Returns the location where cached files will be stored.

Definition at line 88 of file qnetworkdiskcache.cpp.

References d.

Referenced by expire().

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◆ cacheSize()

qint64 QNetworkDiskCache::cacheSize ( ) const

overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 125 of file qnetworkdiskcache.cpp.

References d, expire(), and qDebug.

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◆ clear

void QNetworkDiskCache::clear ( )

overrideslot

\reimp

Definition at line 537 of file qnetworkdiskcache.cpp.

References d, expire(), and qDebug.

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◆ data()

QIODevice * QNetworkDiskCache::data ( const QUrl & url )

overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 357 of file qnetworkdiskcache.cpp.

References QFileDevice::close(), d, file, QUrl::isValid(), QFile::open(), qDebug, QIODevice::readAll(), QIODeviceBase::ReadOnly, remove(), QIODeviceBase::Unbuffered, and url.

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◆ expire()

qint64 QNetworkDiskCache::expire ( )

protectedvirtual

Cleans the cache so that its size is under the maximum cache size.

Returns the current size of the cache.

When the current size of the cache is greater than the maximumCacheSize() older cache files are removed until the total size is less then 90% of maximumCacheSize() starting with the oldest ones first using the file creation date to determine how old a cache file is.

Subclasses can reimplement this function to change the order that cache files are removed taking into account information in the application knows about that QNetworkDiskCache does not, for example the number of times a cache is accessed.