Accessing a delegate's input value from the model - qt

Question

I'm using a custom QTableView with a custom QAbstractTableModel and a QItemDelegate. I'd need to access the contents of the delegate's editor while the user is editing it, and after several attempts, I couldn't find anything satisfying.
Indeed, I've tried several things.
First: trying to access the delegate's current input (created through createEditor) through a property defined in QItemDelegate but... it seems that none exists. That's why I tried to add a QWidget* editor property and setting it in the createEditor.
Unfortunately, QItemDelegate's createEditor is supposed to be const, which makes me unable to set my property there (and since I don't control what calls createEditor, I can't do it before or after).
I don't really know what to do here. Actually, I also needed to know when the user started (or stopped) editing the cell content, which I eventually achieved by creating two const signals (editingStarted and editingStopped). I could probably create a const editorOpened(QWidget*) signal but it just feels bad and ugly...
I can't believe nothing "official" exists to achieve what I'm trying to do, hence this question. If I have everything wrong from the beginning, I'd be glad to know. If you have any other ideas, please suggest.
EDIT: Here is a minimal working example
MainWindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = nullptr);
~MainWindow();
};
#endif // MAINWINDOW_H
MainWindow.cpp
#include "mainwindow.h"
#include <QTableView>
#include "mytableview.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
auto tableView = new MyTableView(this);
setCentralWidget(tableView);
}
MainWindow::~MainWindow()
{
}
MyItemDelegate.h
#ifndef MYITEMDELEGATE_H
#define MYITEMDELEGATE_H
#include <QItemDelegate>
#include <QLineEdit>
#include <QStandardItemModel>
class MyItemDelegate : public QItemDelegate
{
Q_OBJECT
public:
MyItemDelegate(QObject* parent);
virtual QWidget* createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const;
virtual void onCloseEditor();
virtual ~MyItemDelegate() = default;
signals:
// Const signals trick
void editingStarted() const;
void editingFinished() const;
void editorOpened(const QWidget*) const;
};
#endif // MYITEMDELEGATE_H
MyItemDelegate.cpp
#include "myitemdelegate.h"
MyItemDelegate::MyItemDelegate(QObject* parent) : QItemDelegate(parent)
{
connect(this, &QItemDelegate::closeEditor, this, &MyItemDelegate::onCloseEditor);
}
QWidget* MyItemDelegate::createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
auto lineEdit = new QLineEdit(parent);
emit editingStarted();
emit editorOpened(lineEdit);
return lineEdit;
}
void MyItemDelegate::onCloseEditor()
{
emit editingFinished();
}
MyTableView.h
#ifndef MYTABLEVIEW_H
#define MYTABLEVIEW_H
#include <QTableView>
#include <QDebug>
#include "myitemdelegate.h"
class MyTableView : public QTableView
{
Q_OBJECT
public:
explicit MyTableView(QWidget *parent = nullptr);
signals:
public slots:
};
#endif // MYTABLEVIEW_H
MyTableView.cpp
#include "mytableview.h"
MyTableView::MyTableView(QWidget *parent) : QTableView(parent)
{
MyItemDelegate* delegate = new MyItemDelegate(this);
QStandardItemModel* model = new QStandardItemModel(this);
setItemDelegate(delegate);
setModel(model);
QList<QList<QStandardItem*>> items;
for(int i = 0; i < 10; i++)
{
items << QList<QStandardItem*>();
for (int j = 'A'; j < 'E'; j++)
items[i] << new QStandardItem(QString("%1,%2").arg(i).arg(static_cast<char>(j)));
}
for (const auto& row : items)
model->appendRow(row);
connect(delegate, &MyItemDelegate::editingStarted, []() {
qDebug() << "Editing started";
});
connect(delegate, &MyItemDelegate::editingFinished, []() {
qDebug() << "Editing finished";
});
connect(delegate, &MyItemDelegate::editorOpened, [](const QWidget* editor) {
auto lineEdit = qobject_cast<const QLineEdit*>(editor);
connect(lineEdit, &QLineEdit::textChanged, [](const QString& text) {
qDebug() << text;
});
});
}
main.cpp
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}

Answer 1

The following solution maybe fits your needs. I just defined a new signal inside the delegate and connected to it inside the class owning the delegate.
MyItemDelegate.h
#ifndef MYITEMDELEGATE_H
#define MYITEMDELEGATE_H
#include <QStyledItemDelegate>
class MyItemDelegate : public QStyledItemDelegate
{
Q_OBJECT
public:
MyItemDelegate(QObject* parent);
QWidget* createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const;
virtual ~MyItemDelegate() = default;
signals:
void valueChanged(const QString&);
};
#endif // MYITEMDELEGATE_H
MyItemDelegate.cpp
#include "myitemdelegate.h"
#include <QLineEdit>
MyItemDelegate::MyItemDelegate(QObject* parent) : QStyledItemDelegate(parent)
{
}
QWidget* MyItemDelegate::createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
auto lineEdit = new QLineEdit(parent);
connect(lineEdit, &QLineEdit::textChanged, this, &MyItemDelegate::valueChanged);
return lineEdit;
}
MyTableView.cpp
#include "mytableview.h"
#include <QStandardItemModel>
MyTableView::MyTableView(QWidget *parent) : QTableView(parent)
{
MyItemDelegate* delegate = new MyItemDelegate(this);
QStandardItemModel* model = new QStandardItemModel(this);
setItemDelegate(delegate);
setModel(model);
QList<QList<QStandardItem*>> items;
for(int i = 0; i < 10; i++)
{
items << QList<QStandardItem*>();
for (int j = 'A'; j < 'E'; j++)
items[i] << new QStandardItem(QString("%1,%2").arg(i).arg(static_cast<char>(j)));
}
for (const auto& row : items)
model->appendRow(row);
connect(delegate, &MyItemDelegate::valueChanged, [](auto v) { qDebug() << v; });
}