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# QNetworkDiskCache Class Reference
[QtNetwork module]

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

Inherits QAbstractNetworkCache.

### Methods

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

## 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.

### QString QNetworkDiskCache.cacheDirectory (self)

Returns the location where cached files will be stored.

See also setCacheDirectory().

### int QNetworkDiskCache.cacheSize (self)

Reimplemented from QAbstractNetworkCache.cacheSize().

### QNetworkDiskCache.clear (self)

This method is also a Qt slot with the C++ signature `void clear()`.

Reimplemented from QAbstractNetworkCache.clear().

### QIODevice QNetworkDiskCache.data (self, QUrl)

Reimplemented from QAbstractNetworkCache.data().

### int QNetworkDiskCache.expire (self)

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() and fileMetaData().

### QNetworkCacheMetaData QNetworkDiskCache.fileMetaData (self, QString)

Returns the QNetworkCacheMetaData for the cache file fileName.

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

### QNetworkDiskCache.insert (self, QIODevice)

Reimplemented from QAbstractNetworkCache.insert().

### int QNetworkDiskCache.maximumCacheSize (self)

Returns the current maximum size for the disk cache.

See also setMaximumCacheSize().

### QNetworkCacheMetaData QNetworkDiskCache.metaData (self, QUrl)

Reimplemented from QAbstractNetworkCache.metaData().

### QIODevice QNetworkDiskCache.prepare (self, QNetworkCacheMetaData)

Reimplemented from QAbstractNetworkCache.prepare().

### bool QNetworkDiskCache.remove (self, QUrl)

Reimplemented from QAbstractNetworkCache.remove().

### QNetworkDiskCache.setCacheDirectory (self, QString)

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 cacheDirectory() and QDesktopServices.CacheLocation.

### QNetworkDiskCache.setMaximumCacheSize (self, int)

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().

### QNetworkDiskCache.updateMetaData (self, QNetworkCacheMetaData)

Reimplemented from QAbstractNetworkCache.updateMetaData().