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  4. How to implement setHeaderData in a subclass of QAbstractTableModel?
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How to implement setHeaderData in a subclass of QAbstractTableModel?

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  • J jdent

    @Pl45m4 my headerData() is currently:

    QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override
    {
    	if (orientation == Qt::Horizontal)
    	{
    		if (role == Qt::DisplayRole)
    			return QVariant{ tr("Num %1").arg(section) };
    		return "?";
    	}
    	return "---";
    }
    

    I know it isn't correct... please some help.

    Regards,
    Juan

    Christian EhrlicherC Offline
    Christian EhrlicherC Offline
    Christian Ehrlicher
    Lifetime Qt Champion
    wrote on last edited by
    #5

    @jdent said in How to implement setHeaderData in a subclass of QAbstractTableModel?:

    I know it isn't correct... please some help.

    As I already set - you should return the data which was set through setHeaderData() - how should it work otherwise?

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    • Christian EhrlicherC Christian Ehrlicher

      @jdent said in How to implement setHeaderData in a subclass of QAbstractTableModel?:

      I know it isn't correct... please some help.

      As I already set - you should return the data which was set through setHeaderData() - how should it work otherwise?

      J Offline
      J Offline
      jdent
      wrote on last edited by
      #6

      @Christian-Ehrlicher but what should I return when role is Qt::DisplayRole and when role is otherwise?
      Just imagine for now - to simplify the example - that I have no setHeaderData() overload and that I just want "Num 0" for column 0 and "Num 1" for column 1. What should I return for each value of role?

      Christian EhrlicherC J 2 Replies Last reply
      0
      • J Offline
        J Offline
        jdent
        wrote on last edited by
        #7

        what do I need to call in QTableView to display the header of the model?

        1 Reply Last reply
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        • J jdent

          @Christian-Ehrlicher but what should I return when role is Qt::DisplayRole and when role is otherwise?
          Just imagine for now - to simplify the example - that I have no setHeaderData() overload and that I just want "Num 0" for column 0 and "Num 1" for column 1. What should I return for each value of role?

          Christian EhrlicherC Offline
          Christian EhrlicherC Offline
          Christian Ehrlicher
          Lifetime Qt Champion
          wrote on last edited by Christian Ehrlicher
          #8

          @jdent said in How to implement setHeaderData in a subclass of QAbstractTableModel?:

          I just want "Num 0" for column 0 and "Num 1" for column 1. What should I return for each value of role?

          You already return this.

          what do I need to call in QTableView to display the header of the model?

          Nothing - except you've hidden the header by yourself.

          Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
          Visit the Qt Academy at https://academy.qt.io/catalog

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          • Christian EhrlicherC Christian Ehrlicher

            @jdent said in How to implement setHeaderData in a subclass of QAbstractTableModel?:

            I just want "Num 0" for column 0 and "Num 1" for column 1. What should I return for each value of role?

            You already return this.

            what do I need to call in QTableView to display the header of the model?

            Nothing - except you've hidden the header by yourself.

            J Offline
            J Offline
            jdent
            wrote on last edited by
            #9

            @Christian-Ehrlicher "You already return this." No, I don't see any header!!

            "what do I need to call in QTableView to display the header of the model?

            Nothing - except you've hidden the header by yourself." What do you mean, I have hidden the header??

            JonBJ 1 Reply Last reply
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            • J jdent

              @Christian-Ehrlicher "You already return this." No, I don't see any header!!

              "what do I need to call in QTableView to display the header of the model?

              Nothing - except you've hidden the header by yourself." What do you mean, I have hidden the header??

              JonBJ Offline
              JonBJ Offline
              JonB
              wrote on last edited by JonB
              #10

              @jdent
              Your code uses setHeaderData() to explicitly set some header.
              From that method you need to save/store that value. Somewhere in your subclass.
              Then your header() method needs to retrieve that and return it.
              This is what a model like, say, QStandardItemModel will do for you.
              When you use your own QAbstractTableModel you have to implement this. In your own member variable structure. For all roles you wish to allow the caller to store data in header.
              If you do not need to allow callers to set the header data, e.g. you can calculate what you want, then you don't need a setHeaderData() or storage, you can just write header() to compute and return values.
              It's the same principle as what you do with setData() and data() in your subclassed QAbstractTableModel, only done separately for the header data.

              1 Reply Last reply
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              • J Offline
                J Offline
                jdent
                wrote on last edited by
                #11

                QAbstractTableModel has no header() method nor its superclass!!

                Christian EhrlicherC 1 Reply Last reply
                0
                • J jdent

                  QAbstractTableModel has no header() method nor its superclass!!

                  Christian EhrlicherC Offline
                  Christian EhrlicherC Offline
                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on last edited by
                  #12

                  @jdent said in How to implement setHeaderData in a subclass of QAbstractTableModel?:

                  QAbstractTableModel has no header() method nor its superclass!!

                  It's a typo - it's headerData() as you already found out...

                  Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                  Visit the Qt Academy at https://academy.qt.io/catalog

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                  • J jdent

                    @Christian-Ehrlicher but what should I return when role is Qt::DisplayRole and when role is otherwise?
                    Just imagine for now - to simplify the example - that I have no setHeaderData() overload and that I just want "Num 0" for column 0 and "Num 1" for column 1. What should I return for each value of role?

                    J Offline
                    J Offline
                    jdent
                    wrote on last edited by jdent
                    #13

                    @jdent I am needing to repeat myself because my question goes unanswered. please help!
                    What is wrong with my headerData()? The problem is I cannot see the header of my QTableView! What am I doing wrong?

                    JonBJ 1 Reply Last reply
                    0
                    • J jdent

                      @jdent I am needing to repeat myself because my question goes unanswered. please help!
                      What is wrong with my headerData()? The problem is I cannot see the header of my QTableView! What am I doing wrong?

                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by JonB
                      #14

                      @jdent
                      Start by correcting your code, your last 2 return statements are not acceptable for any role.

                      	if (orientation == Qt::Horizontal)
                      	{
                      		if (role == Qt::DisplayRole)
                      			return QVariant{ tr("Num %1").arg(section) };
                      		return QVariant();
                      	}
                      	return QVariant();
                      

                      Then confirm with a breakpoint/debug statement that your headerData() is getting called, and report back.

                      I assume you have a QHeaderView in your QTableView to see the headers?

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                      • J Offline
                        J Offline
                        jdent
                        wrote on last edited by
                        #15

                        ok thanks
                        I get Qt::Vertical with role 13, 6, 0, 1
                        then I get Qt::Horizontal with roles 13, 6, 0, 1
                        I did not have a QHeaderView!! Now I have:

                            ui.tableView->setHorizontalHeader(new QHeaderView{ Qt::Horizontal });
                        

                        and I see a header now!

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                        • J Offline
                          J Offline
                          jdent
                          wrote on last edited by
                          #16

                          But now I cannot sort by column!!
                          and I have

                              VectorModel* model = new VectorModel{ std::unique_ptr<AbstractCollection>(new PersistentCollection{ storage(), select(columns(&Claim::id, &Claim::amount))})};
                              QSortFilterProxyModel* proxy = new QSortFilterProxyModel{ this };
                              proxy->setSourceModel(model);
                              ui.tableView->setModel(proxy);
                              ui.tableView->setHorizontalHeader(new QHeaderView{ Qt::Horizontal });
                              ui.tableView->setSortingEnabled(true);
                              ui.tableView->setSelectionMode(QAbstractItemView::SingleSelection);
                          
                          1 Reply Last reply
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                          • J Offline
                            J Offline
                            jdent
                            wrote on last edited by
                            #17

                            Anyway I needed to modify sorting: how do I take control of it? For instance if the column has text then alphanumerical sorting must be done and if it is numeric, then the text in the cell must be converted to numeric and the order set numerically! How is this done?

                            JonBJ 1 Reply Last reply
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                            • J Offline
                              J Offline
                              jdent
                              wrote on last edited by
                              #18

                              How does one cell's value compare with another? I want to implement intelligent sorting!

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                              • J jdent

                                Anyway I needed to modify sorting: how do I take control of it? For instance if the column has text then alphanumerical sorting must be done and if it is numeric, then the text in the cell must be converted to numeric and the order set numerically! How is this done?

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

                                @jdent
                                You should use a QSortFilterProxyModel for displaying your model sorted.

                                treeView = new QTreeView;
                                model = new YourModel;
                                proxyModel = new QSortFilterProxyModel(this);
                                proxyModel->setSourceModel(model);
                                treeview->setModel(proxyModel);
                                

                                Then you do sorting (and optionally filtering too) in the proxy model code.

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                                • J Offline
                                  J Offline
                                  jdent
                                  wrote on last edited by
                                  #20

                                  I have this but when I click the header nothing happens!

                                  JonBJ 1 Reply Last reply
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                                  • J jdent

                                    I have this but when I click the header nothing happens!

                                    JonBJ Offline
                                    JonBJ Offline
                                    JonB
                                    wrote on last edited by
                                    #21

                                    @jdent
                                    If you go to the doc page I referenced and read through you will find it describes exactly what you need to do and how it relates to QSortFilterProxyModel or sorting your model.

                                    The idea is to read through the documentation, search for examples and ask questions here when you have researched and have a problem.

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                                    • J Offline
                                      J Offline
                                      jdent
                                      wrote on last edited by jdent
                                      #22

                                      Ok, I implemented a subclass of QSortFilterProxyModel in the following :

                                      class SortFilterProxyModel : public QSortFilterProxyModel
                                      {
                                      	Q_OBJECT
                                      public:
                                      	SortFilterProxyModel(QObject* parent = nullptr) : QSortFilterProxyModel(parent) {}
                                      
                                      	bool lessThan(const QModelIndex& source_left, const QModelIndex& source_right) const override
                                      	{
                                      		QVariant left_data = sourceModel()->data(source_left);
                                      		QVariant right_data = sourceModel()->data(source_right);
                                      
                                      		switch (left_data.userType())
                                      		{
                                      		case QMetaType::QDateTime:
                                      			return left_data.toDateTime() < right_data.toDateTime();
                                      		case QMetaType::Int:
                                      			return left_data.toInt() < right_data.toInt();
                                      		case QMetaType::QString:
                                      			return left_data.toString() < right_data.toString();
                                      		default:
                                      			return QSortFilterProxyModel::lessThan(source_left, source_right);
                                      		}
                                      	}
                                      };
                                      

                                      HOWEVER, I click on the header view and nothing happens!! Why?
                                      This is with the subclass and without it!! I would expect resorting to occur in the reverse order when clicking the header but nothing changes!

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                                      • J Offline
                                        J Offline
                                        jdent
                                        wrote on last edited by jdent
                                        #23

                                        Sorting is working fine.... its the header view that does not respond to the mouse! What can be going on with the header?

                                        JonBJ 1 Reply Last reply
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                                        • J jdent

                                          Sorting is working fine.... its the header view that does not respond to the mouse! What can be going on with the header?

                                          JonBJ Offline
                                          JonBJ Offline
                                          JonB
                                          wrote on last edited by JonB
                                          #24

                                          @jdent
                                          Did you look at the docs page? Did you follow the Sorting section code?

                                          Although it does no harm, with what is in your lessThan() at present I don't think you needed to override it. QSortFilterProxyModel::lessThan() already handles the types you have coded for. But if you were to change the behaviour that's where you would do it.

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