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Thread: QNetworkAccessManager within QThread

  1. #1
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    Default QNetworkAccessManager within QThread

    Hey,

    I'm trying to make an application that is designed to grab data from a website in a thread but for some reason, despite having no errors in compile/run, the slot never seems to get fired.

    Heres my code:

    Qt Code:
    1. void itemthread::run() {
    2. int i;
    3. QTextStream out(stdout, QIODevice::WriteOnly);
    4. for(i=1; i < 10; i++) {
    5. out << i;
    6. QNetworkAccessManager *manager = new QNetworkAccessManager();
    7. connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(gotData(QNetworkReply *)));
    8.  
    9. QString url_string = QString("http://www.someurl.com?arg=%1").arg(i);
    10. QUrl url(url_string);
    11.  
    12. QNetworkRequest request;
    13. request.setUrl(url);
    14. request.setRawHeader("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)");
    15.  
    16. manager->get(request);
    17. }
    18. }
    To copy to clipboard, switch view to plain text mode 

    "itemthread" is a class that extends QThread. My slot "gotData" never seems to be fired, no matter how long you leave the program running. I had to remove this from new QNetworkAccessManager because it was causing a error during runtime ("QObject: Cannot create children for a parent that is in a different thread.").

    How can I request URLs while inside a QThread?

    Thanks,

    Tom

  2. #2
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    Default Re: QNetworkAccessManager within QThread

    My guess is that your thread does not have an event loop. Try a simple experiment and create a QEventLoop and call exec on it.

    Also, I assume that you are taking care of delete the allocated network managers and such somewhere.

  3. #3
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    Default Re: QNetworkAccessManager within QThread

    Make sure that you have gotData(QNetworkReply *) is defined in your *.h file as a slot.

    If you have it defined as a standard function the compiler will not give you an error but it will not work.

    Something like:

    slot:
    void gotData(QNetworkReply *trigger);

    BTW: I found this out the hard way.

  4. #4
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    Default Re: QNetworkAccessManager within QThread

    I have the same problem, when i put the code in the constructor the slot is working but when i put it in the run method it doesn't work , someone know why ?

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    Default Re: QNetworkAccessManager within QThread

    Quote Originally Posted by hassinoss View Post
    someone know why ?
    Yes, easy, you have done something wrong.

    Cheers,
    _

  6. #6
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    Default Re: QNetworkAccessManager within QThread

    This is my code
    Qt Code:
    1. Manager::Manager(QWidget *parent)
    2. {
    3. m_url.setUrl("http://time.jsontest.com/");
    4. m_request.setUrl(m_url);
    5. connect(&m_networkManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(onResult(QNetworkReply*)));*/
    6. m_networkManager.get(m_request);
    7. }
    8.  
    9. void Manager::onResult(QNetworkReply* reply)
    10. {
    11. if(reply)
    12. {
    13. QString data = (QString) reply->readAll();
    14.  
    15. ......;
    16. }
    17. }
    18.  
    19. void Manager::run()
    20. {
    21. while(true)
    22. {
    23.  
    24. }
    25. }
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    whene i put the code in the constructor in the run method it doesn't work , there is any problem with doing this

  7. #7
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    Default Re: QNetworkAccessManager within QThread

    Well, assuming that "Manager" is a QThread, it has a weird parent (QWidget can't live in a secondary thread).

    Also the networkmanager is created in the context of the thread running the manager constructor, so it will do its event processing in that thread, not in the context of the "Manager" thread.

    Your run() method also looks suspiciously like it doesn't run the thread's event loop, but since the code is missing this is just a wild guess.

    Cheers,
    _

  8. #8
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    Default Re: QNetworkAccessManager within QThread

    I changed the run method with a method with a loop for with 10 loops, and i see that it wait the end of the loop and it enter after that to the onResult method 10 times.

  9. #9
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    Default Re: QNetworkAccessManager within QThread

    So your loop enters event processing by calling exec() and each time your slot is invoked you quit() the event loop and continue in your outer loop?

    Why not just count the invocations and quit on the last one?

    Cheers,
    _

  10. #10
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    Default Re: QNetworkAccessManager within QThread

    No what i want is for each loop the onResult must be invoked, but im my case its invoked just until the end of the loop.

  11. #11
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    Default Re: QNetworkAccessManager within QThread

    Your posting is missing the code for the loop. Again.

    What do you need the thread for anyway?

    Cheers,
    _

  12. #12
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    Default Re: QNetworkAccessManager within QThread

    The is the same in the constructor , i just replace it

    this is the code for the loop :

    Qt Code:
    1. void Manager::run()
    2. {
    3. while(true)
    4. {
    5. m_url.setUrl("http://time.jsontest.com/");
    6. m_request.setUrl(m_url);
    7. connect(&m_networkManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(onResult(QNetworkReply*)));*/
    8. m_networkManager.get(m_request);
    9. }
    10. }
    To copy to clipboard, switch view to plain text mode 

    i need the thread to send many requests and get many replies.

  13. #13
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    Default Re: QNetworkAccessManager within QThread

    Quote Originally Posted by hassinoss View Post
    The is the same in the constructor , i just replace it

    this is the code for the loop :

    Qt Code:
    1. void Manager::run()
    2. {
    3. while(true)
    4. {
    5. m_url.setUrl("http://time.jsontest.com/");
    6. m_request.setUrl(m_url);
    7. connect(&m_networkManager, SIGNAL(finished(QNetworkReply*)), this, SLOT(onResult(QNetworkReply*)));*/
    8. m_networkManager.get(m_request);
    9. }
    10. }
    To copy to clipboard, switch view to plain text mode 
    And you disconnect where? Or do you want to multiply the number of slot invocation on each loop?
    The network manager is still owned by the main thread (the thread that created it), so is the receiver object (this).
    All processing other than the loop happens in the creating thread.

    Are you sure that is what you want?

    Quote Originally Posted by hassinoss View Post
    i need the thread to send many requests and get many replies.
    No, I mean, what do you need the thread for. Sending and receiving multiple requests does not need threads, so you must have some other reason do use one, no?

    Cheers,
    _

  14. #14
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    Default Re: QNetworkAccessManager within QThread

    What i want exactly is recover data from the web service in real time ( every seconde for example) that's why i used the threads, is there an other way to do this i can use it ?

  15. #15
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    Default Re: QNetworkAccessManager within QThread

    Have you tested that it does not work with just the main thread?

    Cheers,
    _

  16. #16
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    Default Re: QNetworkAccessManager within QThread

    What do you mean by the main thread ?

  17. #17
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    Default Re: QNetworkAccessManager within QThread

    The thread executing QApplication::exec()

    Cheers,
    _

  18. #18
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    Default Re: QNetworkAccessManager within QThread

    I didn't get realy what you mean but Wysoka answered me in the other Thread http://www.qtcentre.org/threads/6008...iples-requests

    Thanx for your help

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