Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. QML and Qt Quick
  4. QML and JSON
Forum Updated to NodeBB v4.3 + New Features

QML and JSON

Scheduled Pinned Locked Moved QML and Qt Quick
23 Posts 12 Posters 54.7k Views 1 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • C Offline
    C Offline
    Cezary Tomczak
    wrote on last edited by
    #9

    Parsing JSON is easy and no additional libraries are required, you can just use eval(), JSON structure is a valid javascript code, right?

    1 Reply Last reply
    0
    • D Offline
      D Offline
      DenisKormalev
      wrote on last edited by
      #10

      Cezary Tomczak, yes, but you need to build model from object you will receive after eval, it will take processor time, not JSON parsing.

      1 Reply Last reply
      0
      • S Offline
        S Offline
        SimonJudge
        wrote on last edited by
        #11

        Having done some more research, Cezary is correct. While it would be nice to have a JSONListModel, something similar can be achieved using the sample shown at http://bugreports.qt.nokia.com/browse/QTBUG-12117

        After other comments it would be useful to know the performance implications of doing this vs doing it in Qt c++

        Simon Judge

        1 Reply Last reply
        0
        • D Offline
          D Offline
          DenisKormalev
          wrote on last edited by
          #12

          SimonJudge, all depends on your JSON size. If it is not big, than JS way is ok for you. But if it contains a lot of elements, then using c++ will be better.

          1 Reply Last reply
          0
          • 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.

            1 Reply Last reply
            0
            • 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>

              1 Reply Last reply
              0
              • 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

                1 Reply Last reply
                0
                • 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>

                  1 Reply Last reply
                  0
                  • 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

                    1 Reply Last reply
                    0
                    • 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.

                      1 Reply Last reply
                      0
                      • 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

                        1 Reply Last reply
                        0
                        • 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

                          1 Reply Last reply
                          0
                          • 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

                            1 Reply Last reply
                            0
                            • 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>

                              1 Reply Last reply
                              0
                              • 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

                                1 Reply Last reply
                                0

                                • Login

                                • Login or register to search.
                                • First post
                                  Last post
                                0
                                • Categories
                                • Recent
                                • Tags
                                • Popular
                                • Users
                                • Groups
                                • Search
                                • Get Qt Extensions
                                • Unsolved