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QTreeView rowCount() value differs

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  • VRoninV Offline
    VRoninV Offline
    VRonin
    wrote on last edited by VRonin
    #3

    I'm not 100% sure but I think it has to do with lazy loading (QFileSystemModel::fetchMore). When you expand the first time the model did not actually "read" those rows yet.

    If this is the case you can use

    void MainWindow::expand(const QModelIndex &index)
    {
    while(model->canFetchMore(index))
    model->fetchMore(index);
        qDebug() << model->data(index,Qt::DisplayRole);
        qDebug() << model->hasChildren(index);
        qDebug() << model->hasIndex(0,0,index);
        qDebug() << model->rowCount(index) ;
    }
    

    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
    ~Napoleon Bonaparte

    On a crusade to banish setIndexWidget() from the holy land of Qt

    V 1 Reply Last reply
    0
    • VRoninV VRonin

      I'm not 100% sure but I think it has to do with lazy loading (QFileSystemModel::fetchMore). When you expand the first time the model did not actually "read" those rows yet.

      If this is the case you can use

      void MainWindow::expand(const QModelIndex &index)
      {
      while(model->canFetchMore(index))
      model->fetchMore(index);
          qDebug() << model->data(index,Qt::DisplayRole);
          qDebug() << model->hasChildren(index);
          qDebug() << model->hasIndex(0,0,index);
          qDebug() << model->rowCount(index) ;
      }
      
      V Offline
      V Offline
      Vinoth Rajendran4
      wrote on last edited by Vinoth Rajendran4
      #4

      @VRonin : Tried your approach, still issue is seen.

      model->canFetchMore(index)
      

      return false always....

      Is there any specific reason why model not reading its row contents during the very first expansion ???

      Thank You!

      1 Reply Last reply
      0
      • VRoninV Offline
        VRoninV Offline
        VRonin
        wrote on last edited by
        #5

        Can you try adding Qt::QueuedConnection as the last argument to your connect and see if it works then?

        "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
        ~Napoleon Bonaparte

        On a crusade to banish setIndexWidget() from the holy land of Qt

        V 1 Reply Last reply
        0
        • VRoninV VRonin

          Can you try adding Qt::QueuedConnection as the last argument to your connect and see if it works then?

          V Offline
          V Offline
          Vinoth Rajendran4
          wrote on last edited by Vinoth Rajendran4
          #6

          @VRonin , with Qt::QueuedConnection also, issue is seen.

          Can this be a bug ???

          JonBJ VRoninV 2 Replies Last reply
          0
          • V Vinoth Rajendran4

            @VRonin , with Qt::QueuedConnection also, issue is seen.

            Can this be a bug ???

            JonBJ Offline
            JonBJ Offline
            JonB
            wrote on last edited by JonB
            #7

            @Vinoth-Rajendran4

            Can this be a bug ???

            We don't know yet. Does it matter? At this point I assume you're looking for a workaround.

            Given that @VRonin's suggestions have not worked, at this point if it were me: I would test your code which outputs the numbers by calling it from your expand() via a single-shot QTimer with a delay of, say, a second. Let's see whether by any chance there's some OS activity going on which does not properly expand a top-level volume directory immediately and only really does it asynchronously? Does this behaviour happen on any directory node in the tree, or only certain ones (like, only volume ones)?

            V 1 Reply Last reply
            0
            • JonBJ JonB

              @Vinoth-Rajendran4

              Can this be a bug ???

              We don't know yet. Does it matter? At this point I assume you're looking for a workaround.

              Given that @VRonin's suggestions have not worked, at this point if it were me: I would test your code which outputs the numbers by calling it from your expand() via a single-shot QTimer with a delay of, say, a second. Let's see whether by any chance there's some OS activity going on which does not properly expand a top-level volume directory immediately and only really does it asynchronously? Does this behaviour happen on any directory node in the tree, or only certain ones (like, only volume ones)?

              V Offline
              V Offline
              Vinoth Rajendran4
              wrote on last edited by Vinoth Rajendran4
              #8

              @JonB : your workaround suggestion with single-shot timer , works fine.

              Does this behaviour happen on any directory node in the tree, or only certain ones (like, only volume ones)?
              

              It happens on every directory node in the tree...

              JonBJ 1 Reply Last reply
              0
              • V Vinoth Rajendran4

                @JonB : your workaround suggestion with single-shot timer , works fine.

                Does this behaviour happen on any directory node in the tree, or only certain ones (like, only volume ones)?
                

                It happens on every directory node in the tree...

                JonBJ Offline
                JonBJ Offline
                JonB
                wrote on last edited by
                #9

                @Vinoth-Rajendran4

                your workaround suggestion with single-shot timer , works fine.

                So, let's be clear. You only get (normally) get a count of 0 first time. If you make it so the first time you examine the children is a second after the expansion was performed it does produce the correct count. Is that what you are saying?

                If it happens on every directory, my impression is there would be code out there which simply does not work. It's like your expand() is being called at the very start of the expansion, but it's the expanded slot and that should be called after the expand has been acted on, I assume.

                1 Reply Last reply
                0
                • SGaistS Offline
                  SGaistS Offline
                  SGaist
                  Lifetime Qt Champion
                  wrote on last edited by
                  #10

                  Hi,

                  Is Media a system disk or an external storage ?

                  Interested in AI ? www.idiap.ch
                  Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                  JonBJ V 2 Replies Last reply
                  0
                  • V Vinoth Rajendran4

                    @VRonin , with Qt::QueuedConnection also, issue is seen.

                    Can this be a bug ???

                    VRoninV Offline
                    VRoninV Offline
                    VRonin
                    wrote on last edited by
                    #11

                    @Vinoth-Rajendran4 said in QTreeView rowCount() value differs:

                    Can this be a bug ???

                    Can you provide a minimum example to replicate the problem? if we can confirm the bug we cat take a look if it's solvable

                    "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                    ~Napoleon Bonaparte

                    On a crusade to banish setIndexWidget() from the holy land of Qt

                    V 2 Replies Last reply
                    0
                    • SGaistS SGaist

                      Hi,

                      Is Media a system disk or an external storage ?

                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by JonB
                      #12

                      @SGaist said in QTreeView rowCount() value differs:

                      Is Media a system disk or an external storage ?

                      I wondered about this (slow external media gets updated "slowly" under Windows). That's why I asked the OP when it happens

                      Does this behaviour happen on any directory node in the tree, or only certain ones (like, only volume ones)?

                      but he says

                      It happens on every directory node in the tree...

                      so assuming that's true it's not to do with media type.

                      1 Reply Last reply
                      0
                      • SGaistS SGaist

                        Hi,

                        Is Media a system disk or an external storage ?

                        V Offline
                        V Offline
                        Vinoth Rajendran4
                        wrote on last edited by
                        #13

                        @SGaist : Media is System disk

                        1 Reply Last reply
                        0
                        • VRoninV VRonin

                          @Vinoth-Rajendran4 said in QTreeView rowCount() value differs:

                          Can this be a bug ???

                          Can you provide a minimum example to replicate the problem? if we can confirm the bug we cat take a look if it's solvable

                          V Offline
                          V Offline
                          Vinoth Rajendran4
                          wrote on last edited by
                          #14

                          @VRonin : my entire code below,

                          MainWindow::MainWindow(QWidget *parent) :
                              QMainWindow(parent),
                              ui(new Ui::MainWindow)
                          {
                              ui->setupUi(this);
                          
                              model = new QFileSystemModel;
                              model->setRootPath("");
                          
                              ui->treeView->setModel(model);
                              ui->treeView->setRootIndex(model->index(""));
                              connect(ui->treeView,SIGNAL(expanded(QModelIndex)),this,SLOT(func(QModelIndex)));
                          }
                          
                          void MainWindow::func(QModelIndex index)
                          {
                                qDebug() << model->data(index1,Qt::DisplayRole);
                               qDebug() << model->hasChildren(index1);
                               qDebug() << model->hasIndex(0,0,index1);
                               qDebug() << model->rowCount(index1);
                          }
                          
                          1 Reply Last reply
                          0
                          • VRoninV VRonin

                            @Vinoth-Rajendran4 said in QTreeView rowCount() value differs:

                            Can this be a bug ???

                            Can you provide a minimum example to replicate the problem? if we can confirm the bug we cat take a look if it's solvable

                            V Offline
                            V Offline
                            Vinoth Rajendran4
                            wrote on last edited by
                            #15

                            @VRonin : the reason why rowcount() is 0 , might be justified with this link , http://doc.qt.io/qt-5/qfilesystemmodel.html#caching-and-performance .

                            Not sure though. Can you please provide your insight .

                            JonBJ 1 Reply Last reply
                            0
                            • V Vinoth Rajendran4

                              @VRonin : the reason why rowcount() is 0 , might be justified with this link , http://doc.qt.io/qt-5/qfilesystemmodel.html#caching-and-performance .

                              Not sure though. Can you please provide your insight .

                              JonBJ Offline
                              JonBJ Offline
                              JonB
                              wrote on last edited by JonB
                              #16

                              @Vinoth-Rajendran4
                              That link includes:

                              Unlike QDirModel, QFileSystemModel uses a separate thread to populate itself so it will not cause the main thread to hang as the file system is being queried. Calls to rowCount() will return 0 until the model populates a directory.

                              It says it's using a separate thread. You said you tried my suggestion of making the debug calls to the functions not start till a second after the expansion and that did make them return the correct answers. If you put that together with the separate thread....

                              I think you should try putting a slot on the http://doc.qt.io/qt-5/qfilesystemmodel.html#directoryLoaded signal. Let's see it report on which directories it finished loading when? Compare when those signals arrive to the value of your rowCount() etc.

                              If that indeed explains the behaviour, you may have to rewrite your code a bit so that you use that signal in combination with the expanded one so that you can get your results reliably?

                              V 1 Reply Last reply
                              2
                              • JonBJ JonB

                                @Vinoth-Rajendran4
                                That link includes:

                                Unlike QDirModel, QFileSystemModel uses a separate thread to populate itself so it will not cause the main thread to hang as the file system is being queried. Calls to rowCount() will return 0 until the model populates a directory.

                                It says it's using a separate thread. You said you tried my suggestion of making the debug calls to the functions not start till a second after the expansion and that did make them return the correct answers. If you put that together with the separate thread....

                                I think you should try putting a slot on the http://doc.qt.io/qt-5/qfilesystemmodel.html#directoryLoaded signal. Let's see it report on which directories it finished loading when? Compare when those signals arrive to the value of your rowCount() etc.

                                If that indeed explains the behaviour, you may have to rewrite your code a bit so that you use that signal in combination with the expanded one so that you can get your results reliably?

                                V Offline
                                V Offline
                                Vinoth Rajendran4
                                wrote on last edited by Vinoth Rajendran4
                                #17

                                @JonB : Seems, during the very first time expansion of a directory , slot of expanded() signal is called ahead of directoryLoaded() , hence the rowCount() is 0.
                                But during subsequent expansion of the same directory, slot of directoryLoaded() is called ahead of expanded() signal , hence now i am receiving correct rowCount() value.

                                Seems a little code alternation might do the trick.

                                JonBJ 2 Replies Last reply
                                1
                                • V Vinoth Rajendran4

                                  @JonB : Seems, during the very first time expansion of a directory , slot of expanded() signal is called ahead of directoryLoaded() , hence the rowCount() is 0.
                                  But during subsequent expansion of the same directory, slot of directoryLoaded() is called ahead of expanded() signal , hence now i am receiving correct rowCount() value.

                                  Seems a little code alternation might do the trick.

                                  JonBJ Offline
                                  JonBJ Offline
                                  JonB
                                  wrote on last edited by
                                  #18

                                  @Vinoth-Rajendran4 That sounds exactly what I was anticipating....

                                  1 Reply Last reply
                                  1
                                  • V Vinoth Rajendran4

                                    @JonB : Seems, during the very first time expansion of a directory , slot of expanded() signal is called ahead of directoryLoaded() , hence the rowCount() is 0.
                                    But during subsequent expansion of the same directory, slot of directoryLoaded() is called ahead of expanded() signal , hence now i am receiving correct rowCount() value.

                                    Seems a little code alternation might do the trick.

                                    JonBJ Offline
                                    JonBJ Offline
                                    JonB
                                    wrote on last edited by
                                    #19

                                    @Vinoth-Rajendran4
                                    I imagine that the first directoryLoaded corresponds to separate thread actually reading from the OS file system. That takes "a bit of time". But subsequent directoryLoaded signals just correspond to QFileSystemModel looking up in its cache and seeing that directory has already been loaded. Hence the variation in the timing of when the signals arrive. Something like that.

                                    1 Reply Last reply
                                    1
                                    • V Offline
                                      V Offline
                                      Vinoth Rajendran4
                                      wrote on last edited by
                                      #20

                                      Thanks @JonB , @SGaist , @VRonin for your suggestions...

                                      1 Reply Last reply
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