Dynamically change delegate QTableView

SGaist

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.

EagleWatch

Hi @SGaist,

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

mrjj

@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.

EagleWatch

@mrjj
Here is how my program looks like.

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

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.

SGaist

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 ?

EagleWatch

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.

mrjj

@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.

EagleWatch

@mrjj
Hi,

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

mrjj

@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.

EagleWatch

@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 ?

mrjj

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.

EagleWatch

@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 ?

mrjj

@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
    {
    }
};

EagleWatch

@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.

mrjj

@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

}

EagleWatch

@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 ?

mrjj

@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
    {
    }
};

EagleWatch

@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 ?

SGaist

Hi,

Can you show how you are using it ?

EagleWatch

@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.