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  4. QML ListView does not reflect updates from its C++ data model [Solved]
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QML ListView does not reflect updates from its C++ data model [Solved]

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  • K Offline
    K Offline
    kwisatz
    wrote on last edited by
    #6

    So, with this the Application no longer crashes but my view still seems to hold the model item's in it's view but the I'm not able to scroll between the items.

    [quote author="ondrejandrej" date="1421854871"]This code works for me:
    @ emit layoutAboutToBeChanged();
    my_data.clear();
    emit layoutChanged();@[/quote]

    As an aside, it'd be nice to find a complete example of a c++ model and a qml view where items are added and removed dynamically but I'm not able to find one online. I'd really appreciate if someone could link it for me.

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    • O Offline
      O Offline
      ondrejandrej
      wrote on last edited by
      #7

      You are creating a model, but it goes out of scope immediately after constructor terminates (I suppose your last code snippet is in a constructor).

      You should ensure that the model remains in existence while the QML view is showing, e. g. by allocating on heap:
      @MyDataModel *myDataModel = new MyDataModel(this);
      context->setContextProperty("myDataModel", myDataModel);@

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      • K Offline
        K Offline
        kwisatz
        wrote on last edited by
        #8

        I've tried to allocate it at the heap as well and the ui remains unchanged. Originally, myDatamodel was a private member of its parent's class. The code snippet was modified to simplify my question.

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        • O Offline
          O Offline
          ondrejandrej
          wrote on last edited by
          #9

          You are using "it's" wrongly. Have a look at http://www.elearnenglishlanguage.com/blog/english-mistakes/its/ . You have it also in the title.

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          • K Offline
            K Offline
            kwisatz
            wrote on last edited by
            #10

            :D Thanks for pointing that out!

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            • p3c0P Offline
              p3c0P Offline
              p3c0
              Moderators
              wrote on last edited by
              #11

              bq. I just tried inserting that, and my Application Crashed as soon as that code was invoked. Narrowed it down to endResetModel() being the culprit.

              I have been using this approach in all my projects where ListView is used. It worked all the time.
              Why are you using QDeclarativeView ? Aren't you using Qt 5 ?

              157

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              • O Offline
                O Offline
                ondrejandrej
                wrote on last edited by
                #12

                [quote author="kwisatz" date="1421877712"]:D Thanks for pointing that out!
                [/quote]
                It's good that you fixed it :D

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                • K Offline
                  K Offline
                  kwisatz
                  wrote on last edited by
                  #13

                  Sorry, should have made this clear earlier on, I'm using Qt 4.8.4.

                  [quote author="p3c0" date="1421902494"]bq. I just tried inserting that, and my Application Crashed as soon as that code was invoked. Narrowed it down to endResetModel() being the culprit.

                  I have been using this approach in all my projects where ListView is used. It worked all the time.
                  Why are you using QDeclarativeView ? Aren't you using Qt 5 ?[/quote]

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                  • p3c0P Offline
                    p3c0P Offline
                    p3c0
                    Moderators
                    wrote on last edited by
                    #14

                    Well then I'm not sure why it crashes. Qt 4.8.4 still is quite old in Qt4 series. Can you try it on Qt 4.8.6 ?

                    157

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                    • K Offline
                      K Offline
                      kwisatz
                      wrote on last edited by
                      #15

                      I've tried this with 4.8.6 but to no avail

                      At the moment, I'm unable to move to Qt5. I'm cross-compiling for an Embedded Linux System as well, there's a fair amount of porting involved to move to Qt5.

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                      • K Offline
                        K Offline
                        kwisatz
                        wrote on last edited by
                        #16

                        Okay, I did manage to get this to work finally.

                        When clearing data, I used:
                        @ beginResetModel();
                        m_data.clear();
                        endResetModel();@

                        When removing an individual item in the data, I used:

                        @ beginRemoveRows(QModelIndex(), index, index);
                        m_data.removeAt(index);
                        endRemoveRows();@

                        And I worked on this bit of code separately from my main application. Will have to see what kind of fun awaits when I merge the changes with the rest of the application ;)

                        Appreciate the help folks!

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