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QML and JSON

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  • L Offline
    L Offline
    luizpaulo
    wrote on last edited by
    #13

    Hey a good Qt/C++ JSON parser is avaliable with a LGPL licence: http://qjson.sourceforge.net/
    Might be what you need.

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    • F Offline
      F Offline
      fcrochik
      wrote on last edited by
      #14

      [quote author="luizpaulo" date="1291470389"]Hey a good Qt/C++ JSON parser is avaliable with a LGPL licence: http://qjson.sourceforge.net/
      Might be what you need.[/quote]

      I saw it when I was working on a simple json parser but decided against it. Depending on the task you can get the same result w/o any additional dependencies - just using the script module.

      Certified Specialist & Qt Ambassador <a href="http://www.crochik.com">Maemo, Meego, Symbian, Playbook, RaspberryPi, Desktop... Qt everywhere!</a>

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      • D Offline
        D Offline
        dridk
        wrote on last edited by
        #15

        Hello here is my point of view! I tested everything! XMLModel, javascript XML parser, C++ side parser etc...

        Do Not use C++ Json parser : Because exchange data between c++ and QML is slow

        Make a Javascript parser ! It's more easy with eval ! Here is an example :

        Json data
        @
        {"index":["all"],"flux":{"all":[{"data":{"title":"boris","icon":"icon.png"}]}}
        @

        QML side : main.qml
        @
        import QtQuick 1.0
        import "parser.js" as JS

        Item {
        id:root
        width: 360
        height: 640

        Component.onCompleted: JS.load()
        
        
        ListModel {  id:listModel }
        
        ListView {
            id:view
            anchors.fill:parent
            model : listModel
            delegate: Rectangle {
                 width:parent.width
                 height:80
                 Text {
                 anchors.center:parent
                 text: title
                 }
               
            }
        }
        

        }
        @

        javascript side : parser.js

        @
        function load() {

        listModel.clear();
        var xhr = new XMLHttpRequest();
        

        xhr.open("GET","http://data.json",true);
        xhr.onreadystatechange = function()
        {
        if ( xhr.readyState == xhr.DONE)
        {
        if ( xhr.status == 200)
        {
        var jsonObject = eval('(' + xhr.responseText + ')');
        loaded(jsonObject)
        }
        }
        }
        xhr.send();
        }

        function loaded(jsonObject)
        {
        for ( var index in jsonObject.flux.all )
        {
        listModel.append({
        "title" : jsonObject.flux.all[index].data["title"],
        "icon" : jsonObject.flux.all[index].data["icon"]});
        }

        // get directly the json object. Should work but not tested
        //listModel.append({jsonObject.flux.all});

        }
        @

        Nothing in Biology Makes Sense Except in the Light of Evolution

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        • F Offline
          F Offline
          fcrochik
          wrote on last edited by
          #16

          It is a little surprising to me that you found that exchanging data between C++ and QML to be slow.

          I can imagine that maybe the C++ xml parser you tried is slow but I can't imagine creating the model in c++ can be any slower than creating it using Javascript.

          Another scenario I can imagine it would slow things is if you are adding elements to a model that is already in use.

          I am just curious of the why...

          Certified Specialist & Qt Ambassador <a href="http://www.crochik.com">Maemo, Meego, Symbian, Playbook, RaspberryPi, Desktop... Qt everywhere!</a>

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          • D Offline
            D Offline
            dridk
            wrote on last edited by
            #17

            That what I m thinking before! But a a guy said me that, and I trust him ... He said me C++ parsing is faster, but exchanging between binary and script is slower.

            So, no matter, the javascript method is a little bit more easy than creating a c++ model ! :)

            Nothing in Biology Makes Sense Except in the Light of Evolution

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            • R Offline
              R Offline
              remy_david
              wrote on last edited by
              #18

              I am also not so happy with the performances of my C++ model but I can't precisely say what's slowing down.

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              • AlicemirrorA Offline
                AlicemirrorA Offline
                Alicemirror
                wrote on last edited by
                #19

                Hi to all,

                I see that the interest in json parsing is always present. I tried to manage qjson but it seems too complex for what can be done and I have developed a method that I am experiencing very efficient and reliable. It concerns of a C++ class and a very short function in js to be used by QML. If someone is interested I can explain it in details in a wiki page. For now the method is integrated in a project but it will be one of the new features of Qt-Complex 2.0 that I am preparing.

                Take a look to http://projects.developer.nokia.com/pricemyhouse.

                Enrico Miglino (aka Alicemirror)
                Balearic Dynamics
                Islas Baleares, Ibiza (Spain)
                www.balearicdynamics.com

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                • P Offline
                  P Offline
                  peppelorum
                  wrote on last edited by
                  #20

                  Please don't use eval when parsing json-data, you are actually running the code, so if something nasty is in the reply you get, well...

                  I've made a small library that plays nice with QML, for making the whole ajax-thingie a bit easier, you can check it out at https://github.com/peppelorum/ajaxmee

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                  • C Offline
                    C Offline
                    Chuck Gao
                    wrote on last edited by
                    #21

                    I think the simplest way to parse and turn json data to C++ model is using QScriptEngine. Please see:
                    @
                    QScriptValue json = m_scriptEngine->evaluate("JSON.parse").call(QScriptValue(), QScriptValueList() << jsonString);
                    QVariantList xxxList = json.toVariant().toList();
                    or
                    QVariantMap xxxMap = json.toVariant().toMap();
                    .....
                    Then, do parse
                    .....
                    @

                    And, in the code, m_scriptEngine is your QScriptEngine, and jsonString is your json data

                    Chuck

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                    • F Offline
                      F Offline
                      fcrochik
                      wrote on last edited by
                      #22

                      QML "includes" a JSON parser. You can just use, without having to include anything:

                      @var obj = JSON.parse( myJSONString );@

                      "See json.org for more details":http://www.json.org/js.html

                      Of course eval can do the trick as well but it is risky and the JSON parser maybe optimized.

                      Certified Specialist & Qt Ambassador <a href="http://www.crochik.com">Maemo, Meego, Symbian, Playbook, RaspberryPi, Desktop... Qt everywhere!</a>

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                      • K Offline
                        K Offline
                        kromain
                        wrote on last edited by
                        #23

                        For anybody still interested, I've just published a JSONListModel component that works just like XMLListModel, but for JSON data instead. It's all pure QML/Javascript, and it even supports queries via JSONPath (XPath for JSON).

                        You can read more about it there: "Devnet article":http://qt-project.org/wiki/JSONListModel

                        Romain Pokrzywka
                        KDAB - http://www.kdab.com

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