blag/post/qt-nearly-synchronous-qnetworkaccessmanager-calls.mdwn

   1 [[!meta title="Qt: (Nearly) synchronous QNetworkAccessManager calls"]]
   2 [[!meta date="2010-07-08"]]
   3 [[!meta author="rohieb"]]
   4 [[!meta license="CC-BY-SA 3.0"]]
   5
   6 The [QNetworkAccessManager][0] class is very user-friendly, but it makes
   7 asynchronous calls. I was in the need for synchronous calls to handle my
   8 HTTP communication, but I did not want the overhead of another thread,
   9 so I googled a bit and finally came up with a short call to an event
  10 loop that processed the request.  Like this:
  11
  12 [[!format c """
  13 QNetworkAccessManager * pnam = new QNetworkAccessManager(this);
  14 // the slot was declared at another place
  15 connect(pnam, SIGNAL(finished(QNetworkReply *)), this,
  16   SLOT(loginFinished(QNetworkReply*)));
  17 QNetworkRequest req(QUrl("http://foo.bar"));
  18 pnam->post(req, postData);
  19
  20 // execute an event loop to process the request (nearly-synchronous)
  21 QEventLoop eventLoop;
  22 // also dispose the event loop after the reply has arrived
  23 connect(pnam, SIGNAL(finished(QNetworkReply *)), &eventLoop, SLOT(quit()));
  24 eventLoop.exec();
  25 """]]
  26
  27 This way my user-defined slot for the `pnam->finished()` signal was
  28 called immediately, and I could be sure to have the HTTP reply at the
  29 end of this code snippet.
  30
  31 Found here: [Qt-Interest Mailing List: QNetworkAccessManager and
  32 QNetworkReply, synchronous][1]
  33
  34 [0]: http://doc.qt.nokia.com/4.6/qnetworkaccessmanager.html
  35 [1]: http://lists.qt.nokia.com/public/qt-interest/2010-April/022031.html
  36
  37 [[!tag howto programming multithreading network Qt signals slots]]