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Dynamically change delegate QTableView



  • I have a QTableView displaying data (filtered) of a QSqlRelationalTableModel.
    I also have a delegate for the second column in my QTableView.

    This delegate provides me to chose an item in a combox.

    My QTableView is displaying filtered data based on another combobox.
    What I would like to get is also change the delegate.

    I can change the relation, howerver, when I'm enterring in the cell to changing value in the combobox, the combobox resets itself to the first relation.

    Here is an example :
    CBO is the combobox outside the QTableView
    CBDEL is the combobox in the QTableView (delegate)

    CBO is getting these values : "Disponibility", "Integrity"
    When the application starts, default value fot CBO is "Disponibility", and CBDEL has these values : "24h" and "72h".

    When I change the CBO to the value "Integrity", the CBDEL should get these values : "Yes" and "No". But it's not.

    I don't know how to manage multiple QAbstractItemDelegate for the same column.

    Here my code :

    evenementsRedoutesModele->setTable("evenementsRedoutes");;
    evenementsRedoutesModele->setEditStrategy(QSqlTableModel::OnManualSubmit);
    evenementsRedoutesModele->setRelation(3, QSqlRelation("critereDisponibilite", "id", "niveau"));
    ui->comboBoxCriteresSecurite->setModel(criteresModele);
    ui->comboBoxCriteresSecurite->setModelColumn(criteresModele->fieldIndex("critere"));
    
    evenementsRedoutesModele->setFilter(QString("id_critere ="
                                                "(SELECT id FROM crit WHERE critere = '%1')").arg(ui->comboBoxCriteresSecurite->currentText()));
    ui->tableViewEvents->setModel(events);
    ui->tableViewEvents->hideColumn(0);
    ui->tableViewEvents->hideColumn(1);
    ui->tableViewEvents->setItemDelegate(new 
    QSqlRelationalDelegate(ui->tableViewEvents));
    connect(ui->comboBoxCriteresSecurite, SIGNAL(currentTextChanged(QString)), this, SLOT(slot_refreshCritSec()));
    
    void slot_refreshCritSec()
    {
        evenetsModele->setFilter(QString("id_critere ="
                                                    "(SELECT id FROM crit WHERE critere = '%1')").arg(string));
    
        ui->tableViewEvenets->reset();
        eventsModele->setRelation(3, QSqlRelation(normalized, "id", "niveau"));
        eventsModele->select();
        ui->tableViewEvents->setItemDelegate(new QSqlRelationalDelegate(ui->tableViewEvents));
    }
    

    The first question is : Is it possible to manage multiple QAbstractItemDelegate for the same column ?
    If yes, how ?


  • Lifetime Qt Champion

    Hi,

    You can change the delegate at any time.

    However, when one wants to have a flexible delegate, he usually builds one that is capable of handling different type of data or load different sets of data into the editor depending on whatever the conditions are.



  • Hi @SGaist,

    What's a flexible delegate ?
    I'm not sure to understand correctly.


  • Lifetime Qt Champion

    @EagleWatch
    Its just a more feature full version of the Delegate. Or you could call it data driven.

    When its time to edit the data, the frameworks calls
    QWidget *MyDelegate::createEditor(QWidget *parent,
    const QStyleOptionViewItem &option,
    const QModelIndex &index) const

    Here you can use a flag, a user role or whatever fits to instruct to create a combobox
    and not LineEdit or what is needed.

    Same applies when writing data back, it must also handle the various Widgets that could be created.
    That way same delegate can be used in various conditions.
    There is ofcourse a fine line of having a monster Delegate or splitting it to multiple ones but in most cases
    handling a few different editors etc is super fine.



  • @mrjj
    Here is how my program looks like.
    0_1525943271361_editor.png

    So I can create an editor for each filter I want ?
    When can I call the editor I want ? The combobox used to filter what the editor shows is edited dynamically. I'm afraid I have to create an editor each time I select an item, but what about the memory ?

    EDIT : With the code I provided, here is what's happening
    0_1525944018845_Capture.JPG
    When the I change the filter (by choosing another item in the combobox), the editor is fine.

    Howerver, when I double click to change the value, the editor is filtered with the first filter I initialized.
    0_1525944231511_Capture.JPG


  • Lifetime Qt Champion

    Something is not completely clear with your setup.

    Do you mean the content of the combo box above the table view depends on the what you selected in one of the rows of said tableview ?

    Or that the content of the cell editor depends on what you selected in the combo box above the table view ?



  • The content of the cell editor should depends on what I select in the combobox above the table view.

    And the content in the combobox above the table view depends on another table view not important here.


  • Lifetime Qt Champion

    @EagleWatch
    hi
    but why you need a new Delegate for that ?
    Could you not just change what ever combobox is using ?
    Like via a slot in Delegate and a signal from mainwindow.



  • @mrjj
    Hi,

    That would be better, but I didn't find how I could do that.


  • Lifetime Qt Champion

    @EagleWatch
    well easy option is just keep Delegate pointer
    around and simply add a new function to it to update List
    via the instance pointer.

    Alternatively add a new slot in Delegate
    void ChangeList(QList<xx> list)
    (should store list for use when editor is created)

    and a new signal in mainwindow
    ( that looks the same)
    and connect them and simple use emit to update the combobox.



  • @mrjj
    That was one of my ideas but I think I don't understand how the delagate works.

    When I study the QSqlRelationnalDelegate, I know the combobox is created with the createEditor function.
    However, I don't understand how to modify the item in the combobox when the editor already exists.

    I think I shoud use the function setEditorData but how to get the editor and the index I have to pass to this function ?


  • Lifetime Qt Champion

    Hi
    Sorry i miss the fact that you use a standard Delegate
    QSqlRelationalDelegate
    and not a custom one.
    I think you need to make a small subclass of QSqlRelationnalDelegate
    and override createEditor so you can adjust whats to happen.

    Since you can call the baseclass's QWidget *QSqlRelationalDelegate::createEditor
    and get the Editor back. the (QWidget *) you can use qobject_cast to convert to
    combobox and hence adjust its items.

    But Maybe this is overkill. I would wait and see if others have easier ideas.



  • @mrjj
    Hi,

    I've thinking about what you said and I tried to create a subclass of QSqlRelationnalDelegate to get Editor back via the createEditor function.

    However the createEditor function is protected, so I cannot override it.
    I have no clue to get Editor back without create my own delegate class.

    As others have not easier ideas, what you suggests might the best for the moment.

    So , how can I override the createEditor function if this is protected ?


  • Lifetime Qt Champion

    @EagleWatch
    Hi
    Whats wrong with

    #include <QtSql/QSqlRelationalDelegate>
    class MySQLDelegate : QSqlRelationalDelegate {
    protected:
        virtual QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const override
        {
            QSqlRelationalDelegate::createEditor(parent,option,index);// call base
        }
        virtual void setEditorData(QWidget *editor, const QModelIndex &index) const override
        {
        }
    };
    


  • @mrjj

    I don't get it. Maybe I need to study a little more in C++.

    That would be what I would like to get :

    #include <QtSql/QSqlRelationalDelegate>
    class MySQLDelegate : QSqlRelationalDelegate {
    protected:
        virtual QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const override
        {
            editor = QSqlRelationalDelegate::createEditor(parent,option,index);// call base
        }
        virtual void setEditorData(QWidget *editor, const QModelIndex &index) const override
        {
        }
    
    private:
        QWidget *editor;
    };
    

    Of course, the code will not work because of the "const" word.


  • Lifetime Qt Champion

    @EagleWatch
    ahh, the const.
    well you dont need to store the Editor as its given in
    setEditorData(QWidget *editor, const QModelIndex &index) const {
    QComboBox *cb=qobject_cast<QComboBox *>(editor);
    if (cb) {
    use combo...
    }

    // handle other types of widgets or send to base setEditorData

    }



  • @mrjj
    Hi,
    I get it, thank you.
    The setEditorData(QWidget *editor, const QModelIndex &index) const {} is protected so I cannot override it.

    delegate.h:18: error : 'virtual void Delegate::setEditorData(QWidget*, const QModelIndex&) const' is protected
         virtual void setEditorData(QWidget *editor, const QModelIndex &index) const
                      ^
    

    This function is not present in the QSqlRelationnalDelegate class.
    Maybe I have to subclass QItemDelegate instead ?


  • Lifetime Qt Champion

    @EagleWatch

    Hi, im missing something. following code compiles with no
    remarks. its listed under protected and im not sure what goes wrong in your case.

    #include <QtSql/QSqlRelationalDelegate>
    class MySQLDelegate : QSqlRelationalDelegate {
    protected:
        virtual QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const override
        {
            QSqlRelationalDelegate::createEditor(parent,option,index);// call base
        }
        virtual void setEditorData(QWidget *editor, const QModelIndex &index) const override
        {
        }
    };
    


  • @mrjj
    I get the error only when I'm using the MySqlDelegate.

    So, in my projectWindow.h, if I have :

    #include "mysqldelegate.h"
    private:
        MySqlDelegate *m_delegate;
    

    I get the issue in the MySqlDelegate class.

    Do you get the issue if you call your class ?


  • Lifetime Qt Champion

    Hi,

    Can you show how you are using it ?



  • @SGaist
    Hi,

    Thank you for asking.
    When searching to answer you, I realized that I forgot to remove some tests with the m_delegate pointer.
    That's why I had the error.

    Now I have all necessary informations, I'll try to customize this subclass to fit with what I want.

    I'll keep you updated guys.

    Thanks.



  • Hi guys,

    I've some news.

    So after some days studying classes I was using, I discoverd that my problem was not because of the QSqlRelationalDelegate class.
    In fact, that was the QSqlRelationalTableModel.

    When I create the QSqlRelationalTableModel, I had to set a relation.
    When doing this, the QSqlRelationalTableModel keeps in cache the model given by the relation.

    Even if we change the relation, the model is still the same, that why the combobox was always showing the same data.

    For now, I just delete the QSqlRelationalTableModel and recreate it with the new relation and it works like a charm.


  • Lifetime Qt Champion

    Do you mean that if you call setRelation a second time it won't work ?



  • Absolutely.

    All tests I've done have confirmed that.
    The model doesn't change at all.


  • Lifetime Qt Champion

    Can you provide a minimal compilable example that shows that ?

    You should also check the bug report system to see if it's something known.



  • Considering we have 3 table :

    Integrity{
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    level VARCHAR(100),
    definition VARCHAR(500)
    }
    Confidentiality{
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    level VARCHAR(100),
    definition VARCHAR(500)
    }
    Proba{
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    id_crit INT,
    somethingelse VARCHAR(500);
    }

    mainWindow.h

    private :
        QSqlRelationalTableModel *m_tableModel;
    
    private slots:
        void slot_refreshRelation();
    

    mainWindow.cpp

    m_tableModel = new QSqlRelationalTableModel();
    m_tableModel->setTable("Proba");
    m_tableModel->setEditStrategy(QSqlTableModel::OnManualSubmit);
    m_tableModel->setRelation(1, QSqlRelation("Integrity", "id", "level"));
    m_tableModel->select();
    
    ui->tableView->setModel(m_tableModel);
    ui->tableView->hideColumn(0);
    ui->tableView->setItemDelegate(new QSqlRelationalDelegate(ui->tableView);
    
    qDebug() << m_tableModel->relationModel(1)->tableName; // Will show : Integrity
    
    connect(ui->pushButton, SIGNAL(clicked()), this, SLOT(slot_refreshRelation()));
    
    void mainWindow::slot_refreshRelation()
    {
        m_table->setRelation(1, QSqlRelation("Confidentiality", "id", "level"));
        m_table->select();
        qDebug() << m_tableModel->relationModel(1)->tableName; // Will show : Integrity
    }
    

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