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How to share Serial port object between two classes

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  • S Offline
    S Offline
    saurabh162
    wrote on last edited by
    #1

    Dear Developers,

    How to share a Serial port between MainWindow(QWidget *parent) and Dialog Class ?

    In my application I have one MainWindow class and another Dialog Box (Dialog Class).

    I open Dialog Box from MainWindow by pressing a button.

    Additionally In order to communicate with hardware I open Serial port in my MainWindow.

    My question is what is correct method to use same serial port(opened in MainWindow) to send commands to hardware, for example if i press some button on dialog box ?

    In other words what is right way to share a serial port object between two classes MainWindow and Dialog Class ?

    Please inform me if you need any other information from me.

    Thank a lot !!

    Regards

    Saurabh

    1 Reply Last reply
    0
    • mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi
      You could use signal and slot instead of sharing the actual QSerial object.
      http://doc.qt.io/qt-5/signalsandslots.html
      So define new slots in Mainwindow that forms your interface the dialog would use.
      Like
      void SendCmd(QByteArray data);

      and in dialog ,
      define new signals for buttons to use
      void SendCmd(QByteArray data); ( yes same name as the slot in main)

      then hook up dialogs signals to mainwindows slot before u call exec() on dialog and
      then u can use serialport from dialog.
      by simply doing
      emit SendCmd(xxxx)

      in buttons click or where u need it.

      Alternatively, just add a parameter to the Dialogs constructor and pass the
      QSerialPort from mainwindow when you construct the Dialog.

      1 Reply Last reply
      7
      • M Offline
        M Offline
        MrShawn
        wrote on last edited by
        #3

        I suggest signals and slots as your first approach.

        You probably want to create a new custom Dialog class which inherits Qts class, this way you can define your new custom signals and emit them when you need to.

        Just as @mrjj said you could pass a pointer to the constructor but again you will need to declare a new custom class for the custom constructor behavior.

        The signals and slots is probably your cleanest approach because you are not passing pointers around and the new custom class would not depend on the serial port.

        Good luck

        1 Reply Last reply
        3
        • S Offline
          S Offline
          saurabh162
          wrote on last edited by
          #4

          Thank you very much mrjj and MrShawn I will try signal and slot approach and will update you.

          regards
          Saurabh

          1 Reply Last reply
          0
          • S Offline
            S Offline
            saurabh162
            wrote on last edited by
            #5

            Hello mrjj and MrShawn,

            signals and slot approach has solved my problem cleanly.

            Thank you very much for help :)

            kind regards
            Saurabh Jain

            1 Reply Last reply
            3
            • S Offline
              S Offline
              saurabh162
              wrote on last edited by
              #6

              Hello Developers,

              As mentioned above I was to send command using signals and slot approach to main window.

              Now I want also to read data received from serial port in MainWindow from Dialog box.

              I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

              thanks you very much :)

              mrjjM jsulmJ aha_1980A 3 Replies Last reply
              0
              • S saurabh162

                Hello Developers,

                As mentioned above I was to send command using signals and slot approach to main window.

                Now I want also to read data received from serial port in MainWindow from Dialog box.

                I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

                thanks you very much :)

                mrjjM Offline
                mrjjM Offline
                mrjj
                Lifetime Qt Champion
                wrote on last edited by
                #7

                @saurabh162
                Hi
                You mean after serial have read all in main, you want to
                send it to a dialog you open ?
                Or do you mean that dialog all reads from serial while data is coming in ?

                S 1 Reply Last reply
                0
                • S saurabh162

                  Hello Developers,

                  As mentioned above I was to send command using signals and slot approach to main window.

                  Now I want also to read data received from serial port in MainWindow from Dialog box.

                  I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

                  thanks you very much :)

                  jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #8

                  @saurabh162 Add a getter method to your dialog:

                  Dialog dialog(this);
                  dialog.exec();
                  MyData data = dialog.data();
                  

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

                  S 1 Reply Last reply
                  0
                  • mrjjM mrjj

                    @saurabh162
                    Hi
                    You mean after serial have read all in main, you want to
                    send it to a dialog you open ?
                    Or do you mean that dialog all reads from serial while data is coming in ?

                    S Offline
                    S Offline
                    saurabh162
                    wrote on last edited by
                    #9

                    @mrjj

                    Hello Mrji,

                    thank you for fast reply

                    Yes, I my application data received from serial port is first stored in buffer in Main Window. I want read this saved data from Dialog box.

                    In dialog box I am sending serial port commands to Main Window using signal and slot. But do not know what is right way to read serial data saved in Main window from Dialog Box.

                    1 Reply Last reply
                    0
                    • jsulmJ jsulm

                      @saurabh162 Add a getter method to your dialog:

                      Dialog dialog(this);
                      dialog.exec();
                      MyData data = dialog.data();
                      
                      S Offline
                      S Offline
                      saurabh162
                      wrote on last edited by
                      #10

                      @jsulm

                      Hello jsulm

                      Thank you for your fast response.

                      I am sorry but i could not understand your solution. I have serial data collected in Main window. This i want to read inside Dialog box.

                      So can you please explain your answer in little details

                      Thank you :)

                      jsulmJ 1 Reply Last reply
                      0
                      • S saurabh162

                        Hello Developers,

                        As mentioned above I was to send command using signals and slot approach to main window.

                        Now I want also to read data received from serial port in MainWindow from Dialog box.

                        I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

                        thanks you very much :)

                        aha_1980A Offline
                        aha_1980A Offline
                        aha_1980
                        Lifetime Qt Champion
                        wrote on last edited by
                        #11

                        @saurabh162 said in How to share Serial port object between two classes:

                        I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

                        Where have you read this? You can surely use signals&slots to exchange data. That's what signals&slots are all about :)

                        Qt has to stay free or it will die.

                        S 1 Reply Last reply
                        2
                        • S saurabh162

                          @jsulm

                          Hello jsulm

                          Thank you for your fast response.

                          I am sorry but i could not understand your solution. I have serial data collected in Main window. This i want to read inside Dialog box.

                          So can you please explain your answer in little details

                          Thank you :)

                          jsulmJ Offline
                          jsulmJ Offline
                          jsulm
                          Lifetime Qt Champion
                          wrote on last edited by
                          #12

                          @saurabh162 You should explain better what you want to do.
                          Pass the data from main window to dialog via constructor:

                          Dialog dialog(this, mySerialData);
                          dialog.exec();
                          

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

                          1 Reply Last reply
                          0
                          • aha_1980A aha_1980

                            @saurabh162 said in How to share Serial port object between two classes:

                            I have read that signal and slot approach is not good to get data or return values. So can you please guide me what can I do ?

                            Where have you read this? You can surely use signals&slots to exchange data. That's what signals&slots are all about :)

                            S Offline
                            S Offline
                            saurabh162
                            wrote on last edited by
                            #13

                            @aha_1980

                            Thank you aha for reply

                            I have read it in following posts

                            https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

                            https://stackoverflow.com/questions/5842124/can-qt-signals-return-a-value

                            According to above posts we should be cautious when we are returning data from a slot.

                            Additionally I have tried it and got segmentation fault. Following are the steps I have taken.

                            1. I have a array " char receive_buffer[RBSIZE]" declared in Main window class with private access. This buffer is always filled with new data when we send serial command from Dialog Box using signal and slot.
                            2. In order to read this buffer, I declared char pointer in my Dialog Box and intialize this pointer to address of "receive_buffer" in Serial communication slot in Main Window.
                            3. After this when I try to read data in receive_buffer[RBSIZE] from Dialog Box using char pointer I get segementation fault.

                            Please let me know if you need any other information.

                            thank you :)

                            aha_1980A 1 Reply Last reply
                            0
                            • S saurabh162

                              @aha_1980

                              Thank you aha for reply

                              I have read it in following posts

                              https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

                              https://stackoverflow.com/questions/5842124/can-qt-signals-return-a-value

                              According to above posts we should be cautious when we are returning data from a slot.

                              Additionally I have tried it and got segmentation fault. Following are the steps I have taken.

                              1. I have a array " char receive_buffer[RBSIZE]" declared in Main window class with private access. This buffer is always filled with new data when we send serial command from Dialog Box using signal and slot.
                              2. In order to read this buffer, I declared char pointer in my Dialog Box and intialize this pointer to address of "receive_buffer" in Serial communication slot in Main Window.
                              3. After this when I try to read data in receive_buffer[RBSIZE] from Dialog Box using char pointer I get segementation fault.

                              Please let me know if you need any other information.

                              thank you :)

                              aha_1980A Offline
                              aha_1980A Offline
                              aha_1980
                              Lifetime Qt Champion
                              wrote on last edited by
                              #14

                              @saurabh162

                              https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

                              Yes, thats bad design. But you don't need to do it like this. You can emit another signal from your dialog when data is ready, and connect it to a slot in your main window.

                              Regards

                              Qt has to stay free or it will die.

                              S 1 Reply Last reply
                              2
                              • aha_1980A aha_1980

                                @saurabh162

                                https://forum.qt.io/topic/11000/getting-a-return-value-from-an-emitted-signal/3

                                Yes, thats bad design. But you don't need to do it like this. You can emit another signal from your dialog when data is ready, and connect it to a slot in your main window.

                                Regards

                                S Offline
                                S Offline
                                saurabh162
                                wrote on last edited by
                                #15

                                @aha_1980

                                ok aha_1980 I try this and will update you ..thanks :)

                                1 Reply Last reply
                                0
                                • S Offline
                                  S Offline
                                  saurabh162
                                  wrote on last edited by
                                  #16

                                  hello aha_1980,

                                  Thank you very much it worked.

                                  I have taken following steps to achieve it. It is working but I also want to ensure whether it is correct way of programming.

                                  1. I have created signal (in Dialog Box) and slot (in main window) with same name
                                    "void ReadSerialBuffer(void);"

                                  2. Declared a array char serialReceivebuffer[RBSIZE]; in dialog box. Additionally a public function "UpdateSerialReadBuffer"in Dialog box to copy data from source buffer to serialReceivebuffer in Dialog Box.

                                  3. After this I defined slot in main window which is calling "UpdateSerialReadBuffer" function of dialog box to copy data from buffer in Main window to buffer in Dialog box.

                                  4. In end I connected both signal and slot using "connect" method

                                  Thank you very much :)

                                  1 Reply Last reply
                                  2
                                  • V Offline
                                    V Offline
                                    viniltc
                                    wrote on last edited by
                                    #17

                                    @saurabh162

                                    I also came across a similar situation. I'm a beginner of Qt and c++. It will be very helpful if you could share a sample code to communicate the serial port object in two forms.

                                    many thanks

                                    1 Reply Last reply
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