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How to use Windows Message Loop and Qt Application Exec?

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  • aha_1980A aha_1980

    Hi @YJCN,

    have you read the (still existing, wow!) links @SGaist recommended?

    You might be interested by QWidget's "winEvent":http://qt-project.org/doc/qt-4.8/qwidget.html#winEvent or QCoreApplication's "winEventFilter":http://qt-project.org/doc/qt-4.8/qcoreapplication.html#winEventFilter

    Regards

    Y Offline
    Y Offline
    YJCN
    wrote on last edited by
    #5

    @aha_1980 Thanks for your reply. I have read the links. In Qt5, the winEvent has been changed to nativeEvent. This is my code.But it doesn't work.

    
    bool MainWindow::nativeEvent(const QByteArray &eventType, void *message, long *result)
    {
        //Q_UNUSED(eventType);
        MSG* msg = reinterpret_cast<MSG*>(message);
        cout<<"in nativeEvent:"<<msg->message<<endl;
        if(msg->message==275)
        {
            //GetMessage(msg, NULL, NULL, NULL);
            TranslateMessage(msg);
            cout << "TranslateMessage" << endl;
            DispatchMessage(msg); // Ends up calling objectEventFnc
            cout << "DispatchMessage" << endl;
            return true;
        }
            return false;
    }
    
    jsulmJ 1 Reply Last reply
    0
    • Y YJCN

      @aha_1980 Thanks for your reply. I have read the links. In Qt5, the winEvent has been changed to nativeEvent. This is my code.But it doesn't work.

      
      bool MainWindow::nativeEvent(const QByteArray &eventType, void *message, long *result)
      {
          //Q_UNUSED(eventType);
          MSG* msg = reinterpret_cast<MSG*>(message);
          cout<<"in nativeEvent:"<<msg->message<<endl;
          if(msg->message==275)
          {
              //GetMessage(msg, NULL, NULL, NULL);
              TranslateMessage(msg);
              cout << "TranslateMessage" << endl;
              DispatchMessage(msg); // Ends up calling objectEventFnc
              cout << "DispatchMessage" << endl;
              return true;
          }
              return false;
      }
      
      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by jsulm
      #6

      @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

      But it doesn't work

      What exactly doesn't work?
      "Note: Events are only delivered to this event handler if the widget is has a native Window handle." from http://doc.qt.io/qt-5/qwidget.html#nativeEvent

      https://forum.qt.io/topic/113070/qt-code-of-conduct

      Y 1 Reply Last reply
      2
      • jsulmJ jsulm

        @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

        But it doesn't work

        What exactly doesn't work?
        "Note: Events are only delivered to this event handler if the widget is has a native Window handle." from http://doc.qt.io/qt-5/qwidget.html#nativeEvent

        Y Offline
        Y Offline
        YJCN
        wrote on last edited by
        #7

        @jsulm I use the Canon EDSDK to control the EOS 800D. I want to download image from camera. after taking picture. In EDSDK, the download is handled by callback function. I test in command line programm ,and there must be this code after sending a take picture command. Otherwise, the programm can't enter the callback funtion.

        MSG msg = { };
        while (GetMessage(&msg, NULL, 0, 0))
        {
            TranslateMessage(&msg);
            DispatchMessage(&msg);
        }
        

        There is the reason I find in Google.

        If you're using the EDSDK on Windows, you have to have a Windows message loop in your main thread, otherwise callbacks won't happen. (This is because the EDSDK uses the obsolete COM STA threading model instead of real threads.)
        

        https://social.microsoft.com/Forums/en-US/a431209c-be99-4394-88b3-59879cb790a4/objecteventhandler-callback-nevercalled?forum=Offtopic
        https://stackoverflow.com/questions/16839640/edsdk-callbacks-not-working/18624865

        mrjjM 1 Reply Last reply
        0
        • Y YJCN

          @jsulm I use the Canon EDSDK to control the EOS 800D. I want to download image from camera. after taking picture. In EDSDK, the download is handled by callback function. I test in command line programm ,and there must be this code after sending a take picture command. Otherwise, the programm can't enter the callback funtion.

          MSG msg = { };
          while (GetMessage(&msg, NULL, 0, 0))
          {
              TranslateMessage(&msg);
              DispatchMessage(&msg);
          }
          

          There is the reason I find in Google.

          If you're using the EDSDK on Windows, you have to have a Windows message loop in your main thread, otherwise callbacks won't happen. (This is because the EDSDK uses the obsolete COM STA threading model instead of real threads.)
          

          https://social.microsoft.com/Forums/en-US/a431209c-be99-4394-88b3-59879cb790a4/objecteventhandler-callback-nevercalled?forum=Offtopic
          https://stackoverflow.com/questions/16839640/edsdk-callbacks-not-working/18624865

          mrjjM Offline
          mrjjM Offline
          mrjj
          Lifetime Qt Champion
          wrote on last edited by
          #8

          @YJCN
          Hi
          in case that nativeEvent simply cannot work with decade-old COM crap (1998)
          there is always the options of using a plain c++ app that will handle the downloading / save to file and
          you simply call it with QProcess from Qt GUI app.

          Y 1 Reply Last reply
          3
          • mrjjM mrjj

            @YJCN
            Hi
            in case that nativeEvent simply cannot work with decade-old COM crap (1998)
            there is always the options of using a plain c++ app that will handle the downloading / save to file and
            you simply call it with QProcess from Qt GUI app.

            Y Offline
            Y Offline
            YJCN
            wrote on last edited by
            #9

            @mrjj The Canon 's demo is using MFC. Why MFC could use?

            jsulmJ mrjjM 2 Replies Last reply
            0
            • Y YJCN

              @mrjj The Canon 's demo is using MFC. Why MFC could use?

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by
              #10

              @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

              Why MFC could use?

              Because it is Microsofts own GUI framework using the Windows event loop...

              https://forum.qt.io/topic/113070/qt-code-of-conduct

              1 Reply Last reply
              2
              • Y YJCN

                @mrjj The Canon 's demo is using MFC. Why MFC could use?

                mrjjM Offline
                mrjjM Offline
                mrjj
                Lifetime Qt Champion
                wrote on last edited by
                #11

                @YJCN
                MFC is very old too :)

                Anyway i wonder with that line

                if(msg->message==275)

                means ? where did u get this magic number from ?

                Y 1 Reply Last reply
                0
                • mrjjM mrjj

                  @YJCN
                  MFC is very old too :)

                  Anyway i wonder with that line

                  if(msg->message==275)

                  means ? where did u get this magic number from ?

                  Y Offline
                  Y Offline
                  YJCN
                  wrote on last edited by
                  #12

                  @mrjj
                  This my CMD programm code

                  int main (){       
                          EdsCameraRef camera;
                  	EdsUInt32 tv;
                          init_camera(camera);
                  	//start_liveview(camera);
                  	//TakePicture(camera);
                  	
                  	take_photo(camera,1,1000);
                  	//TakePhoto();
                  	//dispose(camera);
                  	cout << "before message" << endl;
                  	MSG msg;
                  	while (GetMessage(&msg, NULL, NULL, NULL))
                  	{
                  		cout << "in while" << " msg.message:"<<msg.message<<endl;
                  		TranslateMessage(&msg);
                  		cout << "TranslateMessage" << endl;
                  		DispatchMessage(&msg); // Ends up calling objectEventFnc
                  		cout << "DispatchMessage" << endl;
                  		break;
                  	}
                  	cout << "after message" << endl;
                          EdsCloseSession(camera);
                  	cout << "EdsCloseSession(camera);";
                  	EdsTerminateSDK();
                  	system("pause");
                          return 0;
                  

                  This is output
                  0_1537429196448_3c672381-54c0-4382-832e-91e484ab0433-image.png

                  1 Reply Last reply
                  0
                  • mrjjM Offline
                    mrjjM Offline
                    mrjj
                    Lifetime Qt Champion
                    wrote on last edited by mrjj
                    #13

                    HI
                    ahh, so 275 is the ID for what SDK is doing.
                    So you call
                    init_camera(camera); in main window also ?
                    (and take_photo(camera,1,1000);
                    and camera is a member variable in main window so it doesn't run out of scope?

                    but you never see 275 ? in natvieEvent?

                    Y 1 Reply Last reply
                    0
                    • mrjjM mrjj

                      HI
                      ahh, so 275 is the ID for what SDK is doing.
                      So you call
                      init_camera(camera); in main window also ?
                      (and take_photo(camera,1,1000);
                      and camera is a member variable in main window so it doesn't run out of scope?

                      but you never see 275 ? in natvieEvent?

                      Y Offline
                      Y Offline
                      YJCN
                      wrote on last edited by
                      #14

                      @mrjj Yes. I put the code(init_camera(camera) and take_photo(camera,1,1000) ) in Button's slot function, after taking picture, the programm can't enter callback function(handleObjectEvent) and there is no 275 in natvieEvent.

                      mrjjM 1 Reply Last reply
                      0
                      • Y YJCN

                        @mrjj Yes. I put the code(init_camera(camera) and take_photo(camera,1,1000) ) in Button's slot function, after taking picture, the programm can't enter callback function(handleObjectEvent) and there is no 275 in natvieEvent.

                        mrjjM Offline
                        mrjjM Offline
                        mrjj
                        Lifetime Qt Champion
                        wrote on last edited by
                        #15

                        Hi
                        and just to be 100% sure
                        camera is NOT a local variable in Button's slot function, but in the .h file as a true member of
                        main maindiw (in .h file) ?
                        (im checking its not a death by scope issue)

                        If unsure what i ask, please show full Button's slot function. :)

                        Y 1 Reply Last reply
                        0
                        • mrjjM mrjj

                          Hi
                          and just to be 100% sure
                          camera is NOT a local variable in Button's slot function, but in the .h file as a true member of
                          main maindiw (in .h file) ?
                          (im checking its not a death by scope issue)

                          If unsure what i ask, please show full Button's slot function. :)

                          Y Offline
                          Y Offline
                          YJCN
                          wrote on last edited by
                          #16

                          @mrjj This is Button's slot function code

                          void MainWindow::on_pushButton_2_clicked()
                          {
                              EdsCameraRef camera;
                              init_camera(camera);
                              //start_liveview(camera);
                              //TakePicture(camera);
                              take_photo(camera,1,1000);
                              //TakePhoto();
                              //dispose(camera);
                              cout << "before message" << endl;
                              MSG msg;
                              while (::GetMessage(&msg, NULL, NULL, NULL))
                              {
                                  TranslateMessage(&msg);
                                  DispatchMessage(&msg); // Ends up calling objectEventFnc
                                  break;
                              }
                              cout << "after message" << endl;
                              EdsCloseSession(camera);
                              cout << "EdsCloseSession(camera);";
                              EdsTerminateSDK();
                          }
                          
                          
                          jsulmJ 1 Reply Last reply
                          0
                          • Y YJCN

                            @mrjj This is Button's slot function code

                            void MainWindow::on_pushButton_2_clicked()
                            {
                                EdsCameraRef camera;
                                init_camera(camera);
                                //start_liveview(camera);
                                //TakePicture(camera);
                                take_photo(camera,1,1000);
                                //TakePhoto();
                                //dispose(camera);
                                cout << "before message" << endl;
                                MSG msg;
                                while (::GetMessage(&msg, NULL, NULL, NULL))
                                {
                                    TranslateMessage(&msg);
                                    DispatchMessage(&msg); // Ends up calling objectEventFnc
                                    break;
                                }
                                cout << "after message" << endl;
                                EdsCloseSession(camera);
                                cout << "EdsCloseSession(camera);";
                                EdsTerminateSDK();
                            }
                            
                            
                            jsulmJ Offline
                            jsulmJ Offline
                            jsulm
                            Lifetime Qt Champion
                            wrote on last edited by jsulm
                            #17

                            @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

                            while (::GetMessage(&msg, NULL, NULL, NULL))
                            {
                            TranslateMessage(&msg);
                            DispatchMessage(&msg); // Ends up calling objectEventFnc
                            break;
                            }

                            You execute this loop only once (because of the break).
                            Shouldn't you call break after you got the message you need?

                            @mrjj camera is local :-) but I don't thin this is the issue here.

                            https://forum.qt.io/topic/113070/qt-code-of-conduct

                            mrjjM JonBJ 2 Replies Last reply
                            4
                            • jsulmJ jsulm

                              @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

                              while (::GetMessage(&msg, NULL, NULL, NULL))
                              {
                              TranslateMessage(&msg);
                              DispatchMessage(&msg); // Ends up calling objectEventFnc
                              break;
                              }

                              You execute this loop only once (because of the break).
                              Shouldn't you call break after you got the message you need?

                              @mrjj camera is local :-) but I don't thin this is the issue here.

                              mrjjM Offline
                              mrjjM Offline
                              mrjj
                              Lifetime Qt Champion
                              wrote on last edited by
                              #18

                              @jsulm
                              I agree, it should not run out of scope if it works like we think :)
                              But you are right, maybe it just get first MSG as then it breaks.

                              1 Reply Last reply
                              0
                              • jsulmJ jsulm

                                @YJCN said in How to use Windows Message Loop and Qt Application Exec?:

                                while (::GetMessage(&msg, NULL, NULL, NULL))
                                {
                                TranslateMessage(&msg);
                                DispatchMessage(&msg); // Ends up calling objectEventFnc
                                break;
                                }

                                You execute this loop only once (because of the break).
                                Shouldn't you call break after you got the message you need?

                                @mrjj camera is local :-) but I don't thin this is the issue here.

                                JonBJ Offline
                                JonBJ Offline
                                JonB
                                wrote on last edited by
                                #19

                                @YJCN

                                @jsulm said in How to use Windows Message Loop and Qt Application Exec?:

                                Shouldn't you call break after you got the message you need?

                                Indeed, the loop picks up the first message and that's it. What makes you think that message is the right/only one which needs to be processed this way? It could be any old message....

                                Y 1 Reply Last reply
                                1
                                • JonBJ JonB

                                  @YJCN

                                  @jsulm said in How to use Windows Message Loop and Qt Application Exec?:

                                  Shouldn't you call break after you got the message you need?

                                  Indeed, the loop picks up the first message and that's it. What makes you think that message is the right/only one which needs to be processed this way? It could be any old message....

                                  Y Offline
                                  Y Offline
                                  YJCN
                                  wrote on last edited by
                                  #20

                                  @jsulm @JonB @mrjj Yes, you are right !!! I comment the "break" . It works well!! THANK YOU!☺☺☺☺☺☺☺☺☺☺

                                  JonBJ 1 Reply Last reply
                                  3
                                  • Y YJCN

                                    @jsulm @JonB @mrjj Yes, you are right !!! I comment the "break" . It works well!! THANK YOU!☺☺☺☺☺☺☺☺☺☺

                                    JonBJ Offline
                                    JonBJ Offline
                                    JonB
                                    wrote on last edited by
                                    #21

                                    @YJCN
                                    You have to do more than just comment out the break, if that's what you're saying. If that's all you do the ::GetMessage() loop will never exit, and your code will never return from on_pushButton_2_clicked(), e.g. you cannot press it again to take another photo. Presumably you need to find out whatever is the final message your camera issues on taking a photo and exit the loop once that has been received.

                                    Y 1 Reply Last reply
                                    2
                                    • JonBJ JonB

                                      @YJCN
                                      You have to do more than just comment out the break, if that's what you're saying. If that's all you do the ::GetMessage() loop will never exit, and your code will never return from on_pushButton_2_clicked(), e.g. you cannot press it again to take another photo. Presumably you need to find out whatever is the final message your camera issues on taking a photo and exit the loop once that has been received.

                                      Y Offline
                                      Y Offline
                                      YJCN
                                      wrote on last edited by
                                      #22

                                      @JonB Yes. I just use a five times for loop to solve it . ^_^

                                      JonBJ 1 Reply Last reply
                                      0
                                      • Y YJCN

                                        @JonB Yes. I just use a five times for loop to solve it . ^_^

                                        JonBJ Offline
                                        JonBJ Offline
                                        JonB
                                        wrote on last edited by
                                        #23

                                        @YJCN
                                        I don't know if your response is serious or amused. Doing it "five times" is very flaky. Isn't there a particular message number you get which you need to wait for to indicate it's now OK to leave the loop?

                                        1 Reply Last reply
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