内容

• 公共函数
• 重实现公共函数
• 公共槽
• 保护函数
• 详细描述

QNetworkDiskCache 类

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

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

• 所有成员列表，包括继承成员

公共函数

	QNetworkDiskCache (QObject * parent = Q_NULLPTR)
	~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
virtual QIODevice *	data (const QUrl & url )
virtual void	insert (QIODevice * device )
virtual QNetworkCacheMetaData	metaData (const QUrl & url )
virtual QIODevice *	prepare (const QNetworkCacheMetaData & metaData )
virtual bool	remove (const QUrl & url )
virtual void	updateMetaData (const QNetworkCacheMetaData & metaData )

• 7 public functions inherited from QAbstractNetworkCache
• 32 公共函数继承自 QObject

公共槽

virtual void

clear ()

• 1 公共槽继承自 QAbstractNetworkCache
• 1 公共槽继承自 QObject

保护函数

virtual qint64

expire ()

• 9 保护函数继承自 QObject

额外继承成员

• 1 特性继承自 QObject
• 2 信号继承自 QObject
• 11 静态公共成员继承自 QObject

详细描述

The QNetworkDiskCache class provides a very basic disk cache.

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 = Q_NULLPTR)

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

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 ().

[虚拟] qint64 QNetworkDiskCache:: cacheSize () const

重实现自 QAbstractNetworkCache::cacheSize ().

[virtual slot] void QNetworkDiskCache:: clear ()

重实现自 QAbstractNetworkCache::clear ().

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

重实现自 QAbstractNetworkCache::data ().

[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.

[虚拟] void QNetworkDiskCache:: insert ( QIODevice * device )

重实现自 QAbstractNetworkCache::insert ().

qint64 QNetworkDiskCache:: maximumCacheSize () const

Returns the current maximum size for the disk cache.

另请参阅 setMaximumCacheSize ().

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

重实现自 QAbstractNetworkCache::metaData ().

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

重实现自 QAbstractNetworkCache::prepare ().

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

重实现自 QAbstractNetworkCache::remove ().

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 ().

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

重实现自 QAbstractNetworkCache::updateMetaData ().