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DBus reply data accessed via QString

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  • A Offline
    A Offline
    amonR2
    wrote on last edited by
    #9

    @kshegunov , thank you very much.

    @micland , I don't know how to inspect the reply with the debugger so I prefer to give you the result of qDebug() << args; which is: (QVariant(, )). Should I set Qt or my header in a certain way? So far I use the following includes:

    #include <QtGui> 
    #include <QtDBus/QtDBus>
    

    Is it ok? And what about the Q_DECLARE_METATYPE() that I don't use? Should I use it here? If yes, how?

    miclandM 1 Reply Last reply
    0
    • A amonR2

      @kshegunov , thank you very much.

      @micland , I don't know how to inspect the reply with the debugger so I prefer to give you the result of qDebug() << args; which is: (QVariant(, )). Should I set Qt or my header in a certain way? So far I use the following includes:

      #include <QtGui> 
      #include <QtDBus/QtDBus>
      

      Is it ok? And what about the Q_DECLARE_METATYPE() that I don't use? Should I use it here? If yes, how?

      miclandM Offline
      miclandM Offline
      micland
      wrote on last edited by
      #10

      @amonR2 said:

      I don't know how to inspect the reply with the debugger so I prefer to give you the result of qDebug() << args; which is: (QVariant(, )). Should I set Qt or my header in a certain way?

      The order of the includes should not be relevant.
      According to your debug output your program does not get the same answer as qdbusviewer gets. But I don't think that it's a bug in Qt because qdbusviewer uses the same logic and should be affected by that bug, too.
      Could you check for reply->errorMessage(); and double check if there is any typo in the specified DBus interface / object / method in your code?

      1 Reply Last reply
      0
      • A Offline
        A Offline
        amonR2
        wrote on last edited by
        #11

        @micland said:

        Could you check for reply->errorMessage();

        There sorry but I am not sure what you are talking about, did you mean to do this instead: qDebug() << replyClementine.errroMessage();? If yes, the output is still an empty string (""). For the typo in the DBus interface, objet and method in my code I don't think there is one as qDebug() << replyClementine gives me a correct response. But why this response is not "translated" into a list of variants and strings? What may "corrupt" the process here?

        miclandM 1 Reply Last reply
        0
        • A amonR2

          @micland said:

          Could you check for reply->errorMessage();

          There sorry but I am not sure what you are talking about, did you mean to do this instead: qDebug() << replyClementine.errroMessage();? If yes, the output is still an empty string (""). For the typo in the DBus interface, objet and method in my code I don't think there is one as qDebug() << replyClementine gives me a correct response. But why this response is not "translated" into a list of variants and strings? What may "corrupt" the process here?

          miclandM Offline
          miclandM Offline
          micland
          wrote on last edited by
          #12

          @amonR2
          Yes, I wanted to see that there is no error message provided (or: I was hoping to see a message that gave us a hint ;-) ). I'm a bit confused that there is no error AND no usable reply.
          Another idea: If you don't known how to debug the arguments, can you print out args.count()? Perhaps there is just one entry in the list and this entry might be a new list (or hash map) - and you're accessing the (not existing) second argument.... (the output (QVariant(, )) might indicate that there is just one argument...).

          1 Reply Last reply
          0
          • A Offline
            A Offline
            amonR2
            wrote on last edited by
            #13

            The output of qDebug << args.count(); gives me 1. There is something I have changed in my code's environment: previously it was in release mode and I have just thought to put it in Debug one's which gives more info. With this code:

            QString a1 = args.at(1).toString();
            qDebug() << a1;
            

            my app crashes and the IDE gives me this message: ASSERT failure in QList<T>::at: "index out of range", file /usr/include/qt4/QtCore/qlist.h, line 469. But when I use this one:

            QString a1 = args.at(0).toString();
            qDebug() << a1;
            

            my app doesn't crash and qDebug() gives me an empty string.

            miclandM 1 Reply Last reply
            0
            • A amonR2

              The output of qDebug << args.count(); gives me 1. There is something I have changed in my code's environment: previously it was in release mode and I have just thought to put it in Debug one's which gives more info. With this code:

              QString a1 = args.at(1).toString();
              qDebug() << a1;
              

              my app crashes and the IDE gives me this message: ASSERT failure in QList<T>::at: "index out of range", file /usr/include/qt4/QtCore/qlist.h, line 469. But when I use this one:

              QString a1 = args.at(0).toString();
              qDebug() << a1;
              

              my app doesn't crash and qDebug() gives me an empty string.

              miclandM Offline
              miclandM Offline
              micland
              wrote on last edited by
              #14

              @amonR2
              Ok, the argument list contains just one argument - that's why you get the "index out of range" error because you try to access the second argument. Please add the line qDebug() << args.at(0).typeName(); to see the type of the first argument. Maybe it's a list where you find all your expected data in...

              A 1 Reply Last reply
              0
              • miclandM micland

                @amonR2
                Ok, the argument list contains just one argument - that's why you get the "index out of range" error because you try to access the second argument. Please add the line qDebug() << args.at(0).typeName(); to see the type of the first argument. Maybe it's a list where you find all your expected data in...

                A Offline
                A Offline
                amonR2
                wrote on last edited by
                #15

                The reply from qDebug() << args.at(0).typeName(); gives me: QDBusArgument.

                miclandM 1 Reply Last reply
                0
                • A amonR2

                  The reply from qDebug() << args.at(0).typeName(); gives me: QDBusArgument.

                  miclandM Offline
                  miclandM Offline
                  micland
                  wrote on last edited by
                  #16

                  @amonR2
                  Huh, a nested QDBusArgument? Well check the inner argument if it serves the expected information:
                  args.at(0).value<QDBusArgument>().args().
                  (You should really try to inspect the reply using the debugger and iterate through the object tree to see what's encapsulated in the arguments. That's a lot easier than poking with qDebug() - perhaps this link will help you getting started? http://doc.qt.io/qtcreator/creator-debug-mode.html)

                  1 Reply Last reply
                  0
                  • A Offline
                    A Offline
                    amonR2
                    wrote on last edited by
                    #17

                    @micland said:

                    Huh, a nested QDBusArgument?

                    sorry I don't understand what you mean there but that's all qDebug displays.
                    Then when I try to qDebug thisargs.at(0).value<QDBusArgument>().args();, the compiler says: 'class QDBusArgument' has no member named 'args'. So I tried with this: args.at(0).value<QDBusArgument>() and received the following from the compiler: no match for 'operator<<' in 'qDebug()() << QVariant::value() const [with T = QDBusArgument]()' [...] no known conversion for argument 1 from 'QDebug' to 'QDBusArgument&'.
                    Finally, by puting a breakpoint (thank you for the link) at QList<QVariant> args = replyClementine.arguments(); in my code and launching the debug-mode, the compiler stops and shows me this through the "Locals and Expressions" window:

                    	args                 	<inaccessible>	QList<QVariant>
                    	this	 @0x83f87d8	FenetreNNS
                    		QWidget		QWidget
                    		Deviselabel	0x0	QLabel *
                    		MainLabel	 @0x844d210	QLabel
                    		Nextm	 @0x8451f28	QPushButton
                    		NoTrackLabel	 @0x8454628	QLabel
                    		Play	 @0x844f628	QPushButton
                    		Previous	 @0x8451088	QPushButton
                    		TemoinSousTitre	false	bool
                    		Volume	 @0x8453a48	QSlider
                    		VolumeLabel	 @0x844d160	QLabel
                    		boutonDeviseBaht	 @0x8439978	QPushButton
                    		boutonDeviseDenar	 @0x843cce0	QPushButton
                    		boutonDeviseDollar	 @0x843f968	QPushButton
                    		boutonDeviseEuro	 @0x8440418	QPushButton
                    		boutonDeviseLira	 @0x843e608	QPushButton
                    		boutonDevisePeso	 @0x8442098	QPushButton
                    		boutonDevisePound	 @0x8444e58	QPushButton
                    		boutonDeviseRuble	 @0x843b078	QPushButton
                    		boutonDeviseRupee	 @0x844a4b0	QPushButton
                    		boutonDeviseWon	 @0x844b2e0	QPushButton
                    		boutonDeviseYen	 @0x8448a28	QPushButton
                    		boutonDeviseYuan	 @0x8449e70	QPushButton
                    		iface_Clementine	 @0x845e788	QDBusInterface
                    		machine	 @0x8455420	QStateMachine
                    		principalefen	 @0xbffff7b4	FenPrincipale
                    		replyClementine		QDBusMessage
                    			d_ptr	 @0x845d098	QDBusMessagePrivate
                    		signMapper	 @0x8454ac0	QSignalMapper
                    		signMapper2	 @0x84553e8	QSignalMapper
                    		sliderSousTitre	 @0x844d998	QSlider
                    		state1	 @0x8451f60	QState
                    		state2	 @0x8451f70	QState
                    		str1	"Currency"	QString
                    		tempo	 @0x84505b0	QTimer
                    
                    

                    Should I show the content of some other windows?

                    miclandM 1 Reply Last reply
                    0
                    • A amonR2

                      @micland said:

                      Huh, a nested QDBusArgument?

                      sorry I don't understand what you mean there but that's all qDebug displays.
                      Then when I try to qDebug thisargs.at(0).value<QDBusArgument>().args();, the compiler says: 'class QDBusArgument' has no member named 'args'. So I tried with this: args.at(0).value<QDBusArgument>() and received the following from the compiler: no match for 'operator<<' in 'qDebug()() << QVariant::value() const [with T = QDBusArgument]()' [...] no known conversion for argument 1 from 'QDebug' to 'QDBusArgument&'.
                      Finally, by puting a breakpoint (thank you for the link) at QList<QVariant> args = replyClementine.arguments(); in my code and launching the debug-mode, the compiler stops and shows me this through the "Locals and Expressions" window:

                      	args                 	<inaccessible>	QList<QVariant>
                      	this	 @0x83f87d8	FenetreNNS
                      		QWidget		QWidget
                      		Deviselabel	0x0	QLabel *
                      		MainLabel	 @0x844d210	QLabel
                      		Nextm	 @0x8451f28	QPushButton
                      		NoTrackLabel	 @0x8454628	QLabel
                      		Play	 @0x844f628	QPushButton
                      		Previous	 @0x8451088	QPushButton
                      		TemoinSousTitre	false	bool
                      		Volume	 @0x8453a48	QSlider
                      		VolumeLabel	 @0x844d160	QLabel
                      		boutonDeviseBaht	 @0x8439978	QPushButton
                      		boutonDeviseDenar	 @0x843cce0	QPushButton
                      		boutonDeviseDollar	 @0x843f968	QPushButton
                      		boutonDeviseEuro	 @0x8440418	QPushButton
                      		boutonDeviseLira	 @0x843e608	QPushButton
                      		boutonDevisePeso	 @0x8442098	QPushButton
                      		boutonDevisePound	 @0x8444e58	QPushButton
                      		boutonDeviseRuble	 @0x843b078	QPushButton
                      		boutonDeviseRupee	 @0x844a4b0	QPushButton
                      		boutonDeviseWon	 @0x844b2e0	QPushButton
                      		boutonDeviseYen	 @0x8448a28	QPushButton
                      		boutonDeviseYuan	 @0x8449e70	QPushButton
                      		iface_Clementine	 @0x845e788	QDBusInterface
                      		machine	 @0x8455420	QStateMachine
                      		principalefen	 @0xbffff7b4	FenPrincipale
                      		replyClementine		QDBusMessage
                      			d_ptr	 @0x845d098	QDBusMessagePrivate
                      		signMapper	 @0x8454ac0	QSignalMapper
                      		signMapper2	 @0x84553e8	QSignalMapper
                      		sliderSousTitre	 @0x844d998	QSlider
                      		state1	 @0x8451f60	QState
                      		state2	 @0x8451f70	QState
                      		str1	"Currency"	QString
                      		tempo	 @0x84505b0	QTimer
                      
                      

                      Should I show the content of some other windows?

                      miclandM Offline
                      miclandM Offline
                      micland
                      wrote on last edited by
                      #18

                      @amonR2 said:

                      Huh, a nested QDBusArgument?
                      sorry I don't understand what you mean there but that's all qDebug displays.

                      Aye, sorry - I was wrong, read your answer too fast and got confused...
                      It's hard to find this error without reproducing it. If I find some time at the weekend I'll try to debug it. Can you tell me which software you installed? will say: what's that player your communicating with?

                      A 1 Reply Last reply
                      0
                      • miclandM micland

                        @amonR2 said:

                        Huh, a nested QDBusArgument?
                        sorry I don't understand what you mean there but that's all qDebug displays.

                        Aye, sorry - I was wrong, read your answer too fast and got confused...
                        It's hard to find this error without reproducing it. If I find some time at the weekend I'll try to debug it. Can you tell me which software you installed? will say: what's that player your communicating with?

                        A Offline
                        A Offline
                        amonR2
                        wrote on last edited by
                        #19

                        @micland
                        The name of the player is "Clementine" and I am using Qt 4.8 . No worries, thank you a lot for your help anyway. I will keep looking for a solution. If I can't find anything I will use one of the other APIs. Cheers again.

                        miclandM 2 Replies Last reply
                        0
                        • A amonR2

                          @micland
                          The name of the player is "Clementine" and I am using Qt 4.8 . No worries, thank you a lot for your help anyway. I will keep looking for a solution. If I can't find anything I will use one of the other APIs. Cheers again.

                          miclandM Offline
                          miclandM Offline
                          micland
                          wrote on last edited by
                          #20

                          @amonR2
                          I'm a little bit closer, but did non really succeed...
                          First: Qt 4.8 is some days older, I used 5.6 for my experiements. Inspecting the DBus interface using qdbusviewer (from Qt5.6) ended with the error message "Unable to find method GetMetadata on path /Player in interface org.freedesktop.MediaPlayer" (the method is listed but I can't call it) - but the cli client qdbus provided me the expected data. I can't say if that's a bug in Qt or a "conformity problem", but it shows that calling the clementine DBus interface from Qt works not straight forward.

                          I tried to access the interface using a simple Qt program (like the example code you posted) and got the same reply as you did. Inspecting the received QDBusArgument showed that its currentyType() is a MapType (4) which means that the arguments are organized as a key/value list (the same says the MPRIS spec: see "Metadata" is an array of dict entries in the form (string, variant) eg: {sv}., https://xmms2.org/wiki/MPRIS#.22Metadata.22)

                          I think you have to extract the values manually and play arround with beginMap(), beginMapEntry(), endMapEntry(), endMap() of QDBusArgument. (I spent just a little time but did not succeed ...)
                          But I'm interested if that's the right way so if you find a solution please share it here! (If I find some time I will try it again, too...)

                          1 Reply Last reply
                          1
                          • A amonR2

                            @micland
                            The name of the player is "Clementine" and I am using Qt 4.8 . No worries, thank you a lot for your help anyway. I will keep looking for a solution. If I can't find anything I will use one of the other APIs. Cheers again.

                            miclandM Offline
                            miclandM Offline
                            micland
                            wrote on last edited by
                            #21

                            @amonR2
                            out of curiousity I was looking for a solution (I didn't know before that maps and structs are supported by DBus). And I found a way - using Qt 5.6, but should work with Qt 4.8 as well:

                                // first the same code as you did already
                                QDBusInterface *iface_Clementine = new QDBusInterface("org.mpris.clementine", "/Player", "org.freedesktop.MediaPlayer", QDBusConnection::sessionBus());
                                if(iface_Clementine->isValid()) {
                                    QDBusMessage replyClementine = iface_Clementine->call("GetMetadata");
                                    qDebug() << replyClementine;
                                    // there is just one argument and this argument is a map
                                    QList<QVariant> args = replyClementine.arguments();
                                    const QDBusArgument &arg = args[0].value<QDBusArgument>();
                                    // the map has to be extracted entry by entry which is a tuple of key and value
                                    // in this case, the key is a string but the type of the value depends on the key (string, int, ...)
                                    arg.beginMap();
                                    while (!arg.atEnd()) {
                                        QString key;
                                        QDBusVariant value;
                                        arg.beginMapEntry();
                                        arg >> key >> value;
                                        arg.endMapEntry();
                                        qDebug() << "Key:" << key << "\t\tValue:" << value.variant();
                                    }
                                    arg.endMap();
                                }
                            

                            You still have to inspect the type of the value (depends on what the entry represents: album or track number, or whatever). And the argument parsing can be wrapped in a stream operator, see http://doc.qt.io/qt-5/qdbusargument.html#beginMap-1

                            Some further helpul information can be found here: http://stackoverflow.com/questions/20206376/how-do-i-extract-the-returned-data-from-qdbusmessage-in-a-qt-dbus-call

                            I have no clue why the qdbusviewer of Qt 5.6 is unable to call the DBus method but the code snippet above is working fine.

                            A 1 Reply Last reply
                            1
                            • miclandM micland

                              @amonR2
                              out of curiousity I was looking for a solution (I didn't know before that maps and structs are supported by DBus). And I found a way - using Qt 5.6, but should work with Qt 4.8 as well:

                                  // first the same code as you did already
                                  QDBusInterface *iface_Clementine = new QDBusInterface("org.mpris.clementine", "/Player", "org.freedesktop.MediaPlayer", QDBusConnection::sessionBus());
                                  if(iface_Clementine->isValid()) {
                                      QDBusMessage replyClementine = iface_Clementine->call("GetMetadata");
                                      qDebug() << replyClementine;
                                      // there is just one argument and this argument is a map
                                      QList<QVariant> args = replyClementine.arguments();
                                      const QDBusArgument &arg = args[0].value<QDBusArgument>();
                                      // the map has to be extracted entry by entry which is a tuple of key and value
                                      // in this case, the key is a string but the type of the value depends on the key (string, int, ...)
                                      arg.beginMap();
                                      while (!arg.atEnd()) {
                                          QString key;
                                          QDBusVariant value;
                                          arg.beginMapEntry();
                                          arg >> key >> value;
                                          arg.endMapEntry();
                                          qDebug() << "Key:" << key << "\t\tValue:" << value.variant();
                                      }
                                      arg.endMap();
                                  }
                              

                              You still have to inspect the type of the value (depends on what the entry represents: album or track number, or whatever). And the argument parsing can be wrapped in a stream operator, see http://doc.qt.io/qt-5/qdbusargument.html#beginMap-1

                              Some further helpul information can be found here: http://stackoverflow.com/questions/20206376/how-do-i-extract-the-returned-data-from-qdbusmessage-in-a-qt-dbus-call

                              I have no clue why the qdbusviewer of Qt 5.6 is unable to call the DBus method but the code snippet above is working fine.

                              A Offline
                              A Offline
                              amonR2
                              wrote on last edited by
                              #22

                              @micland

                              WOOW!!! Thank you sooo much micland!! It works!!!
                              I tried a code similar to yours but some data were missing. Just needed to do a very tiny modification on your code:

                              qDebug() << key << value.variant().toString();
                              

                              or directly

                              qDebug() << value.variant().toString();
                              

                              Except it, it is perfect! Thank you again.
                              @micland said:

                              I have no clue why the qdbusviewer of Qt 5.6 is unable to call the DBus method but the code snippet above is working fine.

                              I hope it is going to change as I intend to use it or the 5.7 version very soon.

                              Cheers again.

                              1 Reply Last reply
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