QNetworkDiskCache Class Reference
^{^{[QtNetwork module]}}

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

Methods

__init__ (self, QObject parent = None)
QString cacheDirectory (self)
int cacheSize (self)
clear (self)
QIODevice data (self, QUrl url)
int expire (self)
QNetworkCacheMetaData fileMetaData (self, QString fileName)
insert (self, QIODevice device)
int maximumCacheSize (self)
QNetworkCacheMetaData metaData (self, QUrl url)
QIODevice prepare (self, QNetworkCacheMetaData metaData)
bool remove (self, QUrl url)
setCacheDirectory (self, QString cacheDir)
setMaximumCacheSize (self, int size)
updateMetaData (self, QNetworkCacheMetaData metaData)

Detailed Description

The QNetworkDiskCache class provides a very basic disk cache.

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

Currently you can not share the same cache files with more then 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.nokia.com")));
 manager->get(request);

 // do a request preferred from cache
 QNetworkRequest request2(QUrl(QString("http://qt.nokia.com")));
 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();
 }

Method Documentation

QNetworkDiskCache.init (self, QObject parent = None)

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

Creates a new disk cache. The parent argument is passed to QAbstractNetworkCache's constructor.

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() and fileMetaData().