QQmlNetworkAccessManagerFactory Class

Detailed Description

A QML engine uses QNetworkAccessManager for all network access. By implementing a factory, it is possible to provide the QML engine with custom QNetworkAccessManager instances with specialized caching, proxy and cookies support.

• The QNetworkDiskCache can be used as a request cache with QNetworkDiskCache.
• Using QNetworkProxy, traffic sent by the QNetworkAccessManager can be tunnelled through a proxy.
• Cookies can be saved for future requests by adding a QNetworkCookieJar.

To implement a factory, subclass QQmlNetworkAccessManagerFactory and implement the virtual create() method, then assign it to the relevant QML engine using QQmlEngine::setNetworkAccessManagerFactory(). For instance, the QNetworkAccessManager objects created by the following snippet will cache requests.

 class CachingNetworkAccessManagerFactory : public QQmlNetworkAccessManagerFactory
 {
 public:

     inline QNetworkAccessManager *create(QObject *parent) override
     {
         QNetworkAccessManager *networkAccessManager = new QNetworkAccessManager(parent);
         QNetworkDiskCache *diskCache = new QNetworkDiskCache(parent);
         diskCache->setCacheDirectory("requestCache");
         networkAccessManager->setCache(diskCache);

         return networkAccessManager;
     }
 };

The factory can then be passed to the QML engine so it can instantiate the QNetworkAccessManager with the custom behavior.

 CachingNetworkAccessManagerFactory networkManagerFactory;
 engine->setNetworkAccessManagerFactory(&networkManagerFactory);

Note the QML engine may create QNetworkAccessManager instances from multiple threads. Because of this, the implementation of the create() method must be reentrant. In addition, the developer should be careful if the signals of the object to be returned from create() are connected to the slots of an object that may be created in a different thread:

• The QML engine internally handles all requests, and cleans up any QNetworkReply objects it creates. Receiving the QNetworkAccessManager::finished() signal in another thread may not provide the receiver with a valid reply object if it has already been deleted.
• Authentication details provided to QNetworkAccessManager::authenticationRequired() must be provided immediately, so this signal cannot be connected as a Qt::QueuedConnection (or as the default Qt::AutoConnection from another thread).

For more information about signals and threads, see Threads and QObjects and Signals and Slots Across Threads.