Understanding QAbstractItemDelegate::closeEditor() in Qt Widgets

Purpose

• It's called by the view when editing needs to be concluded, typically due to user interaction (pressing Enter, Tab, or clicking outside the editor) or programmatic actions.
• This virtual function in the QAbstractItemDelegate class is responsible for terminating the editing process of a data item within a Qt view (like QTableView or QListView).

Arguments

• hint (QAbstractItemDelegate::EndEditHint, default=NoHint): An optional argument that provides information about the reason for closing the editor. Possible values include:
  • SubmitAction: Editing was confirmed (e.g., Enter key pressed).
  • RevertAction: Editing was canceled (e.g., Esc key pressed or clicking outside).
  • EscapeAction: Editing was aborted due to an error.
  • NoHint: No specific reason is provided.
• editor (QWidget*): A pointer to the editor widget that was created using createEditor() and used for editing the data.

Behavior

• The implementation of closeEditor() in your custom delegate class should handle the following steps:
  1. Extract data from the editor
     Use the editor widget to retrieve the modified data entered by the user. This might involve reading the value from a QLineEdit, checking the state of a QCheckBox, or any other method specific to the editor type.
  2. (Optional) Validate data
     You can optionally add data validation logic here to ensure the entered data is valid before applying it to the model. If validation fails, you can display an error message or prevent the data from being saved.
  3. (Optional) Update model
     If the data is valid and needs to be saved, use the setModelData() function (also in QAbstractItemDelegate) to apply the changes to the underlying data model. This will trigger updates in the view based on the changes made.
  4. Hide or destroy the editor
     After handling the data, you typically hide or destroy the editor widget using editor->hide() or delete editor (depending on your ownership management).
  5. Emit commitData() signal (optional)
     You can optionally emit the commitData(editor) signal to notify other parts of your application about the successful editing completion.

Example

class MyDelegate : public QStyledItemDelegate {
public:
    QWidget* createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const override {
        // ... (create editor widget here)
    }

    void closeEditor(QWidget* editor, QAbstractItemDelegate::EndEditHint hint) override {
        if (hint == SubmitAction) {
            // Extract data from editor
            QString newText = ((QLineEdit*)editor)->text();

            // Optional data validation (replace with your logic)
            if (newText.isEmpty()) {
                QMessageBox::warning(nullptr, "Error", "Value cannot be empty!");
                return;
            }

            // Update model (assuming the data is valid)
            emit setModelData(editor, model, index);
        }

        // Hide or destroy editor
        editor->hide();
    }
};

• The EndEditHint argument provides additional context about the editing termination.
• Data validation is an optional step you can implement to ensure data integrity.
• Remember to manage the editor widget's lifetime appropriately (hiding or deleting it).
• By overriding closeEditor() in your delegate, you control how editing is finalized and data is handled.

---

#include <QApplication>
#include <QTableView>
#include <QItemDelegate>
#include <QLineEdit>
#include <QMessageBox>

class MyItemDelegate : public QStyledItemDelegate {
public:
    QWidget* createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const override {
        // Create a line edit for editing text
        QLineEdit* editor = new QLineEdit(parent);
        editor->setFrame(false); // Optional: remove editor frame for a cleaner look

        // Set initial text based on model data (assuming a string model)
        QString currentText = index.model()->data(index, Qt::DisplayRole).toString();
        editor->setText(currentText);

        return editor;
    }

    void closeEditor(QWidget* editor, QAbstractItemDelegate::EndEditHint hint) override {
        if (hint == QAbstractItemDelegate::SubmitAction) {
            // Get the modified text from the editor
            QString newText = ((QLineEdit*)editor)->text();

            // Optional data validation (replace with your logic)
            if (newText.isEmpty()) {
                QMessageBox::warning(nullptr, "Error", "Value cannot be empty!");
                return; // Prevent saving if validation fails
            }

            // Update the underlying model data (assuming a string model)
            QModelIndex index = editor->property("modelIndex").toModelIndex();
            index.model()->setData(index, newText, Qt::EditRole);
        }

        // Hide the editor widget
        editor->hide();
    }
};

int main(int argc, char* argv[]) {
    QApplication app(argc, argv);

    // Sample model (replace with your actual model)
    QStringList data;
    data << "Item 1" << "Item 2" << "Item 3";
    QStringListModel model(data);

    // Create a table view and set the delegate
    QTableView tableView;
    tableView.setModel(&model);
    MyItemDelegate delegate;
    tableView.setItemDelegate(&delegate);

    tableView.show();

    return app.exec();
}

In this example:

• Property binding (editor->setProperty("modelIndex", index)) is used to associate the editor with the corresponding model index for data updates.
• The editor widget is hidden using hide() after editing is complete.
• The closeEditor() function retrieves the edited text, performs optional validation, and updates the model if the data is valid.
• The createEditor() function creates a QLineEdit for in-place text editing.

---

1. • Instead of overriding closeEditor(), you could connect to the editingFinished(QWidget* editor, const QModelIndex& index) signal provided by most item view classes (like QTableView or QListView).
   • This signal is emitted when editing is finished, whether by the user or programmatically.
   • Within your slot connected to this signal, you can perform similar actions to closeEditor(), such as retrieving data from the editor, validating it, and updating the model.

2. Manual editing control
   

   • If you have a more complex editing scenario where you want more control over the editing process, you can manage the editor widget yourself without relying on the delegate's closeEditor().
   • This involves manually creating the editor widget, showing it when editing starts, handling user interactions or key presses to commit or cancel editing, and updating the model as needed.

Choosing the right approach

• If you need more granular control over the editing process and want to handle user interactions differently, connecting to the editingFinished signal or manually managing the editor widget might be more suitable.
• If you need a straightforward way to handle basic editing completion and data updates, overriding closeEditor() is a good choice. It provides a convenient framework for these tasks.

Additional considerations

• Data validation is an important aspect of editing and can be implemented in either approach to ensure data integrity.
• Remember to manage the editor widget's lifetime appropriately regardless of the approach you choose. You might need to hide or delete the editor depending on your design.