Custom QStyledItemDelegate to customize apperence of QListView with a SQLModel under the hood

[JonB]

@Andrea_Venturelli
Qt::ItemFlags, including Qt::ItemIsEditable and the flags() method, come from the model, not from the view. So I don't know why you are thinking of subclassing QListView, it does not store item flags or have a flags() method to override.

So you need to change what the model returns. Derive from QAbstractItemModel (or one of its existing derivations) and OR-in the ItemIsEditable to make the model editable. https://doc.qt.io/qt-6/qabstractitemmodel.html#subclassing

To enable editing in your model, you must also implement setData(), and reimplement flags() to ensure that ItemIsEditable is returned.

If you were using a QListWidget which has QListWidgetItems you could call QListWidgetItem::setFlags() to change an item's flags. However that is a "layer" added by QListWidget to the QListView you have. Internally it is presumably implemented by QListWidget storing values to return from its model's flags().

For SQL stuff you should find that QSqlQueryModel returns non-editable flags (cannot edit items returned from a query), unless you subclass it. While QSqlTableModel returns editable flags (can edit items stored in a table). You may want to subclass those, it might also be possible to interpose a (sub-classed) QAbstractProxyModel where you override flags() between your view and the SQL model.

All ways round the one thing you do not need to do is change the QListView :)

[Andrea_Venturelli]

ahaha @JonB you are a legend, and I have a lot to study in order to understand very well the Model\View stuffs.

But bised that, you were right about the QSqlTableModel, and changing the model from QSqlQueryModel to it, "kinda worked"
Now (without trying to subclass anything) I got only the first item editable, and the others do not flinch.

screenshot showing the first item is editable:

based on yours experience, which approach do you think is better and more elegant to resolve the problem (the problem is obviously my ignorance :) )?

[SGaist]

The Query Model Example shows how to make a QSqlQueryModel editable.

[JonB]

@Andrea_Venturelli said in Custom QStyledItemDelegate to customize apperence of QListView with a SQLModel under the hood:

it, "kinda worked"
Now (without trying to subclass anything) I got only the first item editable, and the others do not flinch.

I'm not sure what you're saying. From a QSqlTableModel you should be able to edit any/all columns, e.g. in a QTableView, provided there is nothing "special" about their definitions. Your QListView is only going to show/edit one column. Are you saying you have what you want or something else is a problem?

If what you want to do is edit rows/columns in a SQL table QSqlTableModel should do fine. I think you only would want an editable QSqlQueryModel instead in certain specialised circumstances.

Don't forget there are two possibilities for presenting a UI to edit columns in tables. In one case the user does the edits "in situ" on items in the QTableView, by clicking on them there. This may indeed be what you want. But sometimes you might want to offer a "master-detail" view, where the user clicks on a row in the table view to read whichever editable fields into their own dedicated widgets not sitting on the table view. If you want that Qt offers QDataWidgetMapper. Just so you are aware.

[Andrea_Venturelli]

@JonB
I have a Sql model with all the informations needed to display the custom item inside a list view.

the normal QStyledItemDelegate draw a rectangle with 3 labels (taken from the SqlModel):

• 1. the string rappresenting the date when the message was first posted
• 2. [optional] a string rappresenting the date when the “body” last modification occured (also taken from the Sql model, a empty string is provided if the comment was never edited before)
• 3. the body containing a description about the problem or whatever (also present in the QSqlModel inside its specific column)

When the user double-click the comment he wants to modify, the createEditor() will provide the same data as before (post_date, post_modification_date if available, and the body text) but this time the body_text is not a label or a drawn text but it is a QPlainTextEdit.

I install a filterEvent on the QPlainTextEdit so when the user presses “Ctrl+Return” it emit a CommitAndCloseEditor signal to tell Qt to destroy the editor and save the data to the model (olso adding or updating the post_modified_date).

every rectangle rappresented inside the listView corresponds to a row of the model.

In the screenshot I posted, the first item , when double-clicked, work as expected and the Editor with the QPlainTextEdit. But if I try to do the same with the second, third and so on, the Editor don’t show up.

that’s all for the moment

[JonB]

@Andrea_Venturelli
I guess start by verifying whether the table view is seeing the ItemIsEditable flag for items when you double click (or whatever you have set) to edit them. Since that's talking about editing in place in a QTableView I don't really see how that has anything to do with whatever you are doing with the QListView. Or maybe you don't want cells editable in the QTableView. Or maybe you want clicking in a cell in any column to invoke editing in the QListView. I really don't know.

In the screenshot I posted, the first item , when double-clicked, work as expected and the Editor with the QPlainTextEdit. But if I try to do the same with the second, third and so on, the Editor don’t show up.

First, second and third what?? What's an "item"? Are you talking about coulmns or rows or what? It would be a lot clearer if you stated this sort of thing.

UPDATE
Oh, I think your "items" are lines inside the List Item delegate, each of which corresponds to a column in the table view? So to edit columns within one row in the database. And you are having problems with which item you click and getting into the right edit. Or something like that. Quite outside of anything I have done. I just know about columns/row/cell editing, with or without delegates, of a table model in a QTableView.

[Andrea_Venturelli]

Sorry @JonB I do not repeat an important point that I specified at the very early posts.

the table you see on the right is ONLY FOR DEBUG, on the final widget will only exist the “listView” with the custom delegate.
the table is only needed for me to troubleshoot potential errors and for the other here helping me understand what was given to the ListView!

all the window is a test for develop the listView. it will be a stand alone widget where under it I’ll add a lineEdit to add new comments to the ListView.
THE TABLE IS ONLY FOR REFERENCE!

Sorry if was not clear from the beginning

[JonB]

@Andrea_Venturelli
Yeah, that was my misunderstanding.

You have a delegate which shows all the "columns" in one layout at different places. So won't you have to detect where user clicked to decide which "column" to edit?

[Andrea_Venturelli]

not column , I go by row
every row is a record to my custom item in the ListView

id | body_text | post_date | modified_post_dt
1 basic text 12/02/2024 12/03/2024

displayed as:
—————————-

12/02/2024

12/03/2024

basic text

——————————

[JonB]

@Andrea_Venturelli
Yes I get that now. One list element shows all the columns in a database row, And you don't care where inside that user clicks because you only allow editing the comment column.

So what you are saying is that the first row of the model is editable via the first item in the list view but the second is not, right? :) Then start by printing out the flags() for model index (row) 0 and 1 to verify the latter has ItemIsEditable?

[Andrea_Venturelli]

exactly ! you get it right ahah
I printed the flags and the first give me “isEditable” with all the rest usual thinks (selectable, enabled, nochild)
but all the others don’t have it.. this looks strange to me. I’ll investigate deeper soon and I’ll post if I find something interesting

[JonB]

@Andrea_Venturelli
That comes from the model's flags() implementation. Either you have done something there for row #0 but not others, or if you are saying this is directly the QSqlTableModel then I don't see why it would return different values per row.

[Andrea_Venturelli]

@JonB , @SGaist after a little more debug this is what I noticed:

• 1. the first item I DOUBLE-CLICK (editor trigger for modification) no matter if it was the first ListStyledItemDelegate rappresented in the ListView, the second, the third or the n_th element, became editable and remain editable. After that, all the others items flags are as default ( Selectable and Editable)

as you can see, the fourth item in the list is editable, because it was the first I double clicked.
If I close the application and run it again and double-clicking any other item first, it will be editable and the fourth is only selectable..

• 2. after the body_text being changed, and the key Ctrl+Return being pressed (used for trigger CommitAndClose editor) the method "QStyledItemDelegate::setModelData( param1, param2, param3) doesn't set the new body text correctly as shown here:

void CommentListItem::setModelData( QWidget *editor, QAbstractItemModel *model, const QModelIndex &index ) const
{
    if ( index.siblingAtColumn(2).data().canConvert<QString>() )
    {
        qDebug() << "\n\t[::setModelData()] being called..";  \\ print_1

        CommentEditor* cm_editor = qobject_cast<CommentEditor*>(editor);
        auto cmm_wdg = cm_editor->commentWidget();
        auto body_txt = cmm_wdg.bodyText();

        if ( cm_editor->bodyText() != body_txt )
        {
            qDebug() << "\t[::setModelData()--> body_text different detected] inside if call.."; \\ print_2

            /* generate the edited_mess_date */
            QDateTime time_now = QDateTime::currentDateTime();
            auto edited_mess_date = QString("Last Modification: ");
            edited_mess_date += time_now.toString("ddd, MMM dd HH:mm");

            qDebug() << "\t - 'edited_mess_date' = " << edited_mess_date; \\ print_3

            /* update the model */
            qDebug() << "index.siblingAtColumn(4):\t" << index.siblingAtColumn(4);  \\ print_4
            qDebug() << "index.siblingAtColumn(5):\t" << index.siblingAtColumn(5);  \\ print_5
            model->setData( index.siblingAtColumn(4), QVariant::fromValue( body_txt ) );
            model->setData( index.siblingAtColumn(5), QVariant::fromValue( edited_mess_date ) );
        }
    }
}

the prints are:

Ctrl + Return keys detected
committing editor...
[::setModelData()] being called.. <------- print_1

[::setModelData()--> body_text different detected] inside if call..    <------- print_2

 - 'edited_mess_date' =  "Last Modification: Tue, Nov 05 09:30"  <------- print_3

index.siblingAtColumn(4): QModelIndex(2,4,0x0,QSqlTableModel(0x23a1bceac10)) <------- print_4
index.siblingAtColumn(5): QModelIndex(2,5,0x0,QSqlTableModel(0x23a1bceac10)) <------- print_5

[Andrea_Venturelli]

MainWindow code where the SetUp of the model occur.

private:
Ui::MainWindow ui;
QSqlDatabase _m_db;
QSqlQuery _m_query;
QSqlTableModel _m_model;

MainWidow.cpp

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    this->setUpDb();

    // set the model to QList and QTable
    // _m_model = new QSqlQueryModel;
    _m_model = new QSqlTableModel;

    _m_model->setQuery("SELECT * FROM veh_comments;");

    ui->tb_view->setModel(_m_model);

    auto header = ui->tb_view->horizontalHeader();
    header->setSectionResizeMode(QHeaderView::ResizeToContents);
    ui->tb_view->show();

    ui->lst_vw->setItemDelegate( new CommentListItem );
    ui->lst_vw->setEditTriggers(QAbstractItemView::EditTrigger::DoubleClicked);

    ui->lst_vw->setModel(_m_model);
}


MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_serach_le_returnPressed()
{
    // read the id from the lineEdit
    auto id = ui->serach_le->text();

    if (id == "")
    {
        QSqlQuery query("SELECT * FROM veh_comments");
        _m_model->setQuery(std::move(query));
    } else {
        // UPDATE VIEW
        auto query = commentsPerChassisId(id);
        _m_model->setQuery(std::move(query));
    }
    qDebug() << "Line Edit \"Return_Key\" pressed..\n\n";
}

QSqlQuery MainWindow::commentsPerChassisId(const QString& id)
{
    QSqlQuery my_query(_m_db);
    my_query.prepare(
        "SELECT "
            "veh.*, us.user_name "

            "FROM veh_comments AS veh "
                "INNER JOIN "
                    "users AS us "
                "ON us.id = veh.user_id "
        "WHERE "
            "veh_serial = ? "

        "ORDER BY "
            "comment_datetime DESC "
        );

    my_query.addBindValue(id);
    my_query.exec();

    return my_query;
}

void MainWindow::setUpDb()
{
    _m_db = QSqlDatabase::addDatabase("QPSQL");
    _m_db.setHostName("localhost");
    _m_db.setDatabaseName("test");
    _m_db.setUserName("postgres");
    _m_db.setPassword("MyPostGresPSW0!");


    if (!_m_db.open()) {
        qDebug() << "Error: Could not open database";
    }
}

After the "QStyledItemDelegate::setEditorData()", should I update the model, refresh it or something similar to save permanently the data to the SQL ?

[JonB]

@Andrea_Venturelli
Your posts are large and contain several questions. It's hard to keep up!

I would start by sorting out the editability. Before you double-click to edit, print out the flags() of each item in the model. Do they all contain ItemIsEditable? Then after double-clicking to edit, both then and after the edit is finished, print them all out again. Are you saying some/all of them lose the ItemIsEditable?

doesn't set the new body text correctly as shown

I can't read the screenshot to see what you are saying. Is it just some sort of refresh issue, where the data has changed (automatically shown in the QTableView onto the SQL model) while it remains as-was on the QListView item? Your view needs to know that the model data has changed and refresh accordingly, if it does not already do so automatically (as a QTableView would).

After the "QStyledItemDelegate::setEditorData()", should I update the model, refresh it or something similar to save permanently the data to the SQL ?

You have to start by deciding which QSqlTableModel::EditStrategy you are using/wish to use.

[Andrea_Venturelli]

@JonB I didn't change nothing special beside adding the qDebug() line to print the flags and now all the items are editable and the EditorWidget show up correctly for all ... that's new.

I guess the "editing part is fixed now, but for simplicity I posted all the code on github here: https://github.com/aVenturelli-qt/CommentsListView?tab=readme-ov-file

[SGaist]

You may have missed it but the way to use QSqlTableModel is to set the table you want to use on it rather than the query.

[Andrea_Venturelli]

@SGaist I knew it could potentially become an issue, but I decided to use that model temporarily to create and test the UI.
I guess this is also the cause why I can't subscribe the changes to the model.

Now I'm refactoring the code to make it cleaner, after that I will try to use a QSqlRelationalModel or give up and create a customModel to filter and sort the data without a QFilterSortProxyModel..

this is how my database is Structed at the moment:

[Andrea_Venturelli]

Okay, thanks to everyone who helped me, to resolve the varius bugs and expand my knowlage.
here the recap of how to create and customize the view:

step 1)

Create a normal c++ Class containing the Data you want to display (not inheriting from QWidget)

step 2)

on the Custom Class implement a method "paint(QPainter *painter, const QRect &rect, const QPalette &palette)" that will be used inside the QStyledItemDelegate::paint() method of the custom QStyledItemList for delegating the drawing part to the normal c++ class

step 3)

create a widgetEditor (derived from QWidget) that implement some default Widgets (like QComboBox, QLineEdit, QSpinBox ecc..) to let the user change the data.

When the user have finished to edit, you can provide a "button" to emit a custom signal like "commitAndCloseEditor()" so you can trigger the QStyledItemDelegate::commitData() and closeEditor() signal needed for destroy the Editor once finished the editing.

step 4)

for the custom QStyledItemDelegate to work, you must re-implement the following methods:

• void paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
• QWidget* createEditor( QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index ) const
• void setEditorData( QWidget* editor, const QModelIndex &index ) const
• void setModelData( QWidget *editor, QAbstractItemModel *model, const QModelIndex &index ) const
• QSize sizeHint( const QStyleOptionViewItem &option, const QModelIndex &index )

step 5)

use the method from the QIndexModel to detect if the model have the correct data that can be converted correctly to your vanilla c++ class from the point (1)

NOTE: see the StarDelegate Example provided by Qt. If the underling model have contains a int, using QModelIndex::.data().canConvert<StarRating>() checks if passing a int to the constructor of StarRating will be enough to initialize it.
remember to declare the vanilla c++ class with the Qt's macro like so: Q_DECLARE_METATYPE(StarRating)

you can found the complete code (with notes and comments) on github at: https://github.com/aVenturelli-qt/CommentsListView/tree/main

I still need to fix the data subscription to the model, but this is a separate topic that I will ask on another question if needed. You can find the problems highlighted with a comment like:
/* WARNING HERE */

[Andrea_Venturelli]

for the one interested in this topic, I updated the code on gitHub and now is possible to edit the model and save the changes within the listView with the help of a specialized QStyledItemDelegate.
link: https://github.com/aVenturelli-qt/CommentsListView

In the README there are all the information needed for the setUp and run