QNetworkDiskCache Class▲
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Header: QNetworkDiskCache
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CMake:
find_package(Qt6 REQUIRED COMPONENTS Network)
target_link_libraries(mytarget PRIVATE Qt6::Network)
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qmake: QT += network
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Inherits: QAbstractNetworkCache
Detailed Description▲
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);
diskCache->setCacheDirectory("cacheDir");
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:
// do a normal request (preferred from network, as this is the default)
QNetworkRequest request(QUrl(QString("http://qt-project.org")));
manager->get(request);
// do a request preferred from cache
QNetworkRequest request2(QUrl(QString("http://qt-project.org")));
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();
}Member Function Documentation▲
[explicit] QNetworkDiskCache::QNetworkDiskCache(QObject *parent = nullptr)▲
Creates a new disk cache. The parent argument is passed to QAbstractNetworkCache's constructor.
[virtual] QNetworkDiskCache::~QNetworkDiskCache()▲
Destroys the cache object. This does not clear the disk cache.
QString QNetworkDiskCache::cacheDirectory() const▲
[override virtual] qint64 QNetworkDiskCache::cacheSize() const▲
Reimplements: QAbstractNetworkCache::cacheSize() const.
[override virtual] void QNetworkDiskCache::clear()▲
Reimplements: QAbstractNetworkCache::clear().
[override virtual] QIODevice *QNetworkDiskCache::data(const QUrl &url)▲
Reimplements: QAbstractNetworkCache::data(const QUrl &url).
[virtual protected] qint64 QNetworkDiskCache::expire()▲
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.
cacheSize() calls expire if the current cache size is unknown.
See Also▲
See also maximumCacheSize(), 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.
[override virtual] void QNetworkDiskCache::insert(QIODevice *device)▲
Reimplements: QAbstractNetworkCache::insert(QIODevice *device).
qint64 QNetworkDiskCache::maximumCacheSize() const▲
[override virtual] QNetworkCacheMetaData QNetworkDiskCache::metaData(const QUrl &url)▲
Reimplements: QAbstractNetworkCache::metaData(const QUrl &url).
[override virtual] QIODevice *QNetworkDiskCache::prepare(const QNetworkCacheMetaData &metaData)▲
[override virtual] bool QNetworkDiskCache::remove(const QUrl &url)▲
Reimplements: QAbstractNetworkCache::remove(const QUrl &url).
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▲
See also cacheDirectory(), QStandardPaths::CacheLocation
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▲
See also maximumCacheSize()