QNetworkDiskCache 类

QNetworkDiskCache 类提供非常基本的磁盘缓存。 更多...

头：	#include <QNetworkDiskCache>
qmake:	QT += network
Since:	Qt 4.5
继承：	QAbstractNetworkCache

该类在 Qt 4.5 引入。

• 所有成员列表，包括继承成员

公共函数

	QNetworkDiskCache (QObject * parent = nullptr)
virtual	~QNetworkDiskCache ()
QString	cacheDirectory () const
QNetworkCacheMetaData	fileMetaData (const QString & fileName ) const
qint64	maximumCacheSize () const
void	setCacheDirectory (const QString & cacheDir )
void	setMaximumCacheSize (qint64 size )

重实现公共函数

virtual qint64	cacheSize () const override
virtual QIODevice *	data (const QUrl & url ) override
virtual void	insert (QIODevice * device ) override
virtual QNetworkCacheMetaData	metaData (const QUrl & url ) override
virtual QIODevice *	prepare (const QNetworkCacheMetaData & metaData ) override
virtual bool	remove (const QUrl & url ) override
virtual void	updateMetaData (const QNetworkCacheMetaData & metaData ) override

公共槽

virtual void

clear () override

保护函数

virtual qint64

expire ()

详细描述

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

成员函数文档编制

QNetworkDiskCache:: QNetworkDiskCache ( QObject * parent = nullptr)

Creates a new disk cache. The parent 自变量会被传递给 QAbstractNetworkCache 的构造函数。

[override virtual slot] void QNetworkDiskCache:: clear ()

重实现： QAbstractNetworkCache::clear ().

[虚拟] QNetworkDiskCache:: ~QNetworkDiskCache ()

Destroys the cache object. This does not clear the disk cache.

QString QNetworkDiskCache:: cacheDirectory () const

Returns the location where cached files will be stored.

另请参阅 setCacheDirectory ().

[override virtual] qint64 QNetworkDiskCache:: cacheSize () const

重实现： QAbstractNetworkCache::cacheSize () const.

[override virtual] QIODevice *QNetworkDiskCache:: data (const QUrl & url )

重实现： 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.

注意： cacheSize () calls expire if the current cache size is unknown.

另请参阅 maximumCacheSize () 和 fileMetaData ().

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

返回 QNetworkCacheMetaData for the cache file fileName .

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

[override virtual] void QNetworkDiskCache:: insert ( QIODevice * device )

重实现： QAbstractNetworkCache::insert (QIODevice *device).

qint64 QNetworkDiskCache:: maximumCacheSize () const

Returns the current maximum size for the disk cache.

另请参阅 setMaximumCacheSize ().

[override virtual] QNetworkCacheMetaData QNetworkDiskCache:: metaData (const QUrl & url )

重实现： QAbstractNetworkCache::metaData (const QUrl &url).

[override virtual] QIODevice *QNetworkDiskCache:: prepare (const QNetworkCacheMetaData & metaData )

重实现： QAbstractNetworkCache::prepare (const QNetworkCacheMetaData &metaData).

[override virtual] bool QNetworkDiskCache:: remove (const QUrl & url )

重实现： 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.

另请参阅 cacheDirectory () 和 QDesktopServices::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 ().

另请参阅 maximumCacheSize ().

[override virtual] void QNetworkDiskCache:: updateMetaData (const QNetworkCacheMetaData & metaData )

重实现： QAbstractNetworkCache::updateMetaData (const QNetworkCacheMetaData &metaData).

内容

• 公共函数

• 重实现公共函数

• 公共槽

• 保护函数

• 详细描述