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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
    #4

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

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    • O Offline
      O Offline
      ondrejandrej
      wrote on last edited by
      #5

      This code works for me:
      @ emit layoutAboutToBeChanged();
      my_data.clear();
      emit layoutChanged();@

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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
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                    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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