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Internal/Contributor docs for the Qt SDK. Note: These are NOT official API docs; those are found at https://doc.qt.io/
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QNetworkDiskCache Class Reference

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.
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 isQmlObjectType () const
 Returns whether the object has been created by the QML engine or ownership has been explicitly set via QJSEngine::setObjectOwnership().
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.

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
 Returns the given object cast to type T if the object is of type T (or of a subclass); otherwise returns \nullptr.
 \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 16 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 76 of file qnetworkdiskcache.cpp.

◆ ~QNetworkDiskCache()

QNetworkDiskCache::~QNetworkDiskCache ( )

Destroys the cache object.

This does not clear the disk cache.

Definition at line 84 of file qnetworkdiskcache.cpp.

Member Function Documentation

◆ cacheDirectory()

QString QNetworkDiskCache::cacheDirectory ( ) const

Returns the location where cached files will be stored.

Definition at line 93 of file qnetworkdiskcache.cpp.

◆ cacheSize()

qint64 QNetworkDiskCache::cacheSize ( ) const
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 130 of file qnetworkdiskcache.cpp.

◆ clear

void QNetworkDiskCache::clear ( )
overrideslot

\reimp

Definition at line 532 of file qnetworkdiskcache.cpp.

◆ data()

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

\reimp

Implements QAbstractNetworkCache.

Definition at line 354 of file qnetworkdiskcache.cpp.

◆ 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.

Note
cacheSize() calls expire if the current cache size is unknown.
See also
maximumCacheSize(), fileMetaData()

Definition at line 467 of file qnetworkdiskcache.cpp.

◆ fileMetaData()

QNetworkCacheMetaData QNetworkDiskCache::fileMetaData ( const QString & fileName) const

Returns the QNetworkCacheMetaData for the cache file fileName.

If fileName is not a cache file QNetworkCacheMetaData will be invalid.

Definition at line 334 of file qnetworkdiskcache.cpp.

◆ insert()

void QNetworkDiskCache::insert ( QIODevice * device)
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 192 of file qnetworkdiskcache.cpp.

◆ maximumCacheSize()

qint64 QNetworkDiskCache::maximumCacheSize ( ) const

Returns the current maximum size for the disk cache.

See also
setMaximumCacheSize()

Definition at line 427 of file qnetworkdiskcache.cpp.

◆ metaData()

QNetworkCacheMetaData QNetworkDiskCache::metaData ( const QUrl & url)
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 318 of file qnetworkdiskcache.cpp.

◆ prepare()

QIODevice * QNetworkDiskCache::prepare ( const QNetworkCacheMetaData & metaData)
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 148 of file qnetworkdiskcache.cpp.

◆ remove()

bool QNetworkDiskCache::remove ( const QUrl & url)
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 271 of file qnetworkdiskcache.cpp.

◆ setCacheDirectory()

void QNetworkDiskCache::setCacheDirectory ( const QString & cacheDir)

Sets the directory where cached files will be stored to cacheDir.

QNetworkDiskCache will create this directory if it does not exists.

Prepared cache items will be stored in the new cache directory when they are inserted.

See also
QStandardPaths::CacheLocation

Definition at line 109 of file qnetworkdiskcache.cpp.

◆ setMaximumCacheSize()

void QNetworkDiskCache::setMaximumCacheSize ( qint64 size)

Sets the maximum size of the disk cache to be size.

If the new size is smaller then the current cache size then the cache will call expire().

See also
maximumCacheSize()

Definition at line 440 of file qnetworkdiskcache.cpp.

◆ updateMetaData()

void QNetworkDiskCache::updateMetaData ( const QNetworkCacheMetaData & metaData)
overridevirtual

\reimp

Implements QAbstractNetworkCache.

Definition at line 392 of file qnetworkdiskcache.cpp.

The documentation for this class was generated from the following files: