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Calling static function from QML? Doable?

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

    Hi everyone,

    I'd like to call a static C++ function from QML, but no luck so far. The function is declared in a class NumberMachine exteding QObject like this:

    @
    Q_INVOKABLE static int number();
    @

    The implementation is straightforward, and the class is registered within QML using qmlRegisterUncreatableType() (as it has no public onstructor) ... but the following QML code fails to execute:

    @
    console.log("number: " +NumberMachine.number());
    @

    the engine complains: TypeError: Result of expression 'NumberMachine.number' [undefined] is not a function.

    My question is - is it possible to call static functions from QML at all? If so, does anyone have any idea what I'm missing?

    Thx.

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    • T Offline
      T Offline
      task_struct
      wrote on last edited by
      #2

      Hello,

      you need an instance of NumberMachine

      @
      import QtQuick 1.0

      import MyApp 1.0

      Rectangle {
      width: 360
      height: 360
      Text {
      text: "Hello World"
      anchors.centerIn: parent
      }
      MouseArea {
      anchors.fill: parent
      onClicked: {
      console.log( numberMachine.number() )
      }
      }

      NumberMachine {
          id: numberMachine
      }
      

      }

      @

      "Most good programmers do programming not because they expect to get paid or get adulation by the public, but because it is fun to program."

      • Linu...
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      • S Offline
        S Offline
        SnowmanX
        wrote on last edited by
        #3

        Yeah, that might work for some, but mu NumberMachine is a singleton class - i.e. I cannot create more than one instance of it. Anyway from the post you sent looks like there is no support for calling static functions from QML. Does it apply to QML only or is this unsupported in the script engine?

        Thx.

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        • T Offline
          T Offline
          task_struct
          wrote on last edited by
          #4

          Ahh, I've tried only with static function in NumberMachine and it works.

          Now I've tried with singleton and it seems that you need a public constructor to register class in QML.

          "Most good programmers do programming not because they expect to get paid or get adulation by the public, but because it is fun to program."

          • Linu...
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          • S Offline
            S Offline
            SnowmanX
            wrote on last edited by
            #5

            Right, but that defeats the whole purpose of the singleton - if there is a public constructor, it is no longer singleton ....

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            • M Offline
              M Offline
              mlong
              wrote on last edited by
              #6

              Perhaps you could write a small utility wrapper class which you can instantiate, which then has methods which pass things back and from from the singleton.

              Software Engineer
              My views and opinions do not necessarily reflect those of anyone -- living or dead, real or fictional -- in this universe or any other similar multiverse node. Void where prohibited. Your mileage may vary. Caveat emptor.

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              • S Offline
                S Offline
                SnowmanX
                wrote on last edited by
                #7

                Yeah, doable, but not exactly feasible ... Furthermore I seem to have more problems with enums at this point - the enum declared in the class declaring the static function (the singleton) is not visible to QML when used from the other helper class ... another bummer :(

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                • T Offline
                  T Offline
                  task_struct
                  wrote on last edited by
                  #8

                  You can write a wrapper class that can be instantiated multiple times in QML and communicates with the singleton. It's not pretty, but I don't know what else can be done.

                  Edit:
                  Sorry. I was too slow and there wasn't warning that there are new posts :(

                  "Most good programmers do programming not because they expect to get paid or get adulation by the public, but because it is fun to program."

                  • Linu...
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                  • S Offline
                    S Offline
                    SnowmanX
                    wrote on last edited by
                    #9

                    Thanks guys, I guess I'll try to enter in issue that static functions should be directly callable from QML, as not having this feature is making certain patterns difficult if not impossible (the mentioned problem with enum coming from a different class ...).

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                    • M Offline
                      M Offline
                      mlong
                      wrote on last edited by
                      #10

                      Sounds like a good idea.

                      As an aside, as a workaround, you could -- and yes, I know it's dirty and nasty -- always mirror the enum in the class that's visible to QML.

                      Software Engineer
                      My views and opinions do not necessarily reflect those of anyone -- living or dead, real or fictional -- in this universe or any other similar multiverse node. Void where prohibited. Your mileage may vary. Caveat emptor.

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                      • S Offline
                        S Offline
                        SnowmanX
                        wrote on last edited by
                        #11

                        Thanks for the tip. It might do it for at least some of the usecases.

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                        • M Offline
                          M Offline
                          mlong
                          wrote on last edited by
                          #12

                          If you do add a jira request for the issue, please be sure and add a link to it here for future reference.

                          Software Engineer
                          My views and opinions do not necessarily reflect those of anyone -- living or dead, real or fictional -- in this universe or any other similar multiverse node. Void where prohibited. Your mileage may vary. Caveat emptor.

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                          • M Offline
                            M Offline
                            mbrasser
                            wrote on last edited by
                            #13

                            Hi,

                            For QtQuick 2.0 we are introducing an additional "module API", which should allow you to implement the singleton pattern more easily.

                            The docs for this don't seem to be correctly generated at the moment, but you can view them in source at https://qt.gitorious.org/qt/qtdeclarative/blobs/master/src/declarative/qml/qdeclarative.h (look for qmlRegisterModuleApi)

                            Regards,
                            Michael

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                            • L Offline
                              L Offline
                              lgeyer
                              wrote on last edited by
                              #14

                              [quote author="mbrasser" date="1317857789"]Hi, For QtQuick 2.0 we are introducing an additional "module API", which should allow you to implement the singleton pattern more easily.[/quote]

                              Do you coincidentally know if there is a (provisional) changelog for QtQuick 2.0, a compiled list of (planned) changes or something like that?

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                              • sierdzioS Offline
                                sierdzioS Offline
                                sierdzio
                                Moderators
                                wrote on last edited by
                                #15

                                [quote author="Lukas Geyer" date="1317904148"][quote author="mbrasser" date="1317857789"]Hi, For QtQuick 2.0 we are introducing an additional "module API", which should allow you to implement the singleton pattern more easily.[/quote]

                                Do you coincidentally know if there is a (provisional) changelog for QtQuick 2.0, a compiled list of (planned) changes or something like that?[/quote]

                                Not a real changelog, but at least a glimpse on what's to come: http://doc.qt.nokia.com/qt5-snapshot/qtquick2-whatsnew.html

                                (Z(:^

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                                • L Offline
                                  L Offline
                                  lgeyer
                                  wrote on last edited by
                                  #16

                                  Thanks.

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                                  • S Offline
                                    S Offline
                                    spiritqt
                                    wrote on last edited by
                                    #17

                                    Hi,
                                    you can use approach described "here":http://doc.qt.nokia.com/4.7-snapshot/qtbinding.html#embedding-c-objects-into-qml-components. It works fine for me.

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                                    • S Offline
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                                      steno
                                      wrote on last edited by
                                      #18

                                      [quote author="mbrasser" date="1317857789"]Hi,

                                      For QtQuick 2.0 we are introducing an additional "module API", which should allow you to implement the singleton pattern more easily.

                                      [/quote]

                                      So, is the new module api the function qmlRegisterSingletonType?

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