Introduce QItemDelegate::destroyEditor virtual invoked at editor close

This provides a stronger mechanism e.g when inheriting QItemDelegate.

It makes some things much easier e.g avoid delete of an editor
and maybe only delete depending on what the editor says itself.

This introduces a new virtual function.

Task-number: QTBUG-2299

Change-Id: I8410f8199775987dbacffd99e4c354fdadcdd21f
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

doc/src/examples/spinboxdelegate.qdoc

@@ -55,10 +55,14 @@
     create an editor widget, display it at the correct location in a view,
     and communicate with a model. Custom delegates can also provide their
     own painting code by reimplementing the \c paintEvent() function.
+    Furthermore it is also possible to reuse (and avoid deleting) the editor
+    widget by reimplementing the \a destroyEditor() function. A reused widget
+    could be a mutable member created in the constructor and deleted in
+    the destructor.
 
     \section1 SpinBoxDelegate Class Implementation
 
-    Since the delegate is stateless, the constructor only needs to
+    Delegates are often stateless. The constructor only needs to
     call the base class's constructor with the parent QObject as its
     argument:
 

src/widgets/itemviews/qabstractitemdelegate.cpp

@@ -232,7 +232,7 @@ QAbstractItemDelegate::~QAbstractItemDelegate()
     editor paints its own background (e.g., with
     \l{QWidget::}{setAutoFillBackground()}).
 
-    \sa setModelData() setEditorData()
+    \sa destroyEditor() setModelData() setEditorData()
 */
 QWidget *QAbstractItemDelegate::createEditor(QWidget *,
                                              const QStyleOptionViewItem &,
@@ -241,6 +241,19 @@ QWidget *QAbstractItemDelegate::createEditor(QWidget *,
     return 0;
 }
 
+
+/*!
+    A function called when the editor is no longer needed and should be
+    destroyed. The default behavior is a call to deleteLater on the editor.
+    It possible e.g. to avoid this delete by reimplementing this function.
+
+    \sa createEditor()
+*/
+void QAbstractItemDelegate::destroyEditor(QWidget *editor, const QModelIndex &) const
+{
+    editor->deleteLater();
+}
+
 /*!
     Sets the contents of the given \a editor to the data for the item
     at the given \a index. Note that the index contains information

src/widgets/itemviews/qabstractitemdelegate.h

@@ -88,6 +88,8 @@ public:
                                   const QStyleOptionViewItem &option,
                                   const QModelIndex &index) const;
 
+    virtual void destroyEditor(QWidget *editor, const QModelIndex &index) const;
+
     virtual void setEditorData(QWidget *editor, const QModelIndex &index) const;
 
     virtual void setModelData(QWidget *editor,

src/widgets/itemviews/qabstractitemview.cpp

@@ -1098,7 +1098,7 @@ void QAbstractItemView::reset()
     d->delayedReset.stop(); //make sure we stop the timer
     foreach (const QEditorInfo &info, d->indexEditorHash) {
         if (info.widget)
-            d->releaseEditor(info.widget.data());
+            d->releaseEditor(info.widget.data(), d->indexForEditor(info.widget.data()));
     }
     d->editorIndexHash.clear();
     d->indexEditorHash.clear();
@@ -2778,7 +2778,7 @@ void QAbstractItemView::closeEditor(QWidget *editor, QAbstractItemDelegate::EndE
         editor = ed;
 
         if (!isPersistent && editor)
-            d->releaseEditor(editor);
+            d->releaseEditor(editor, index);
     }
 
     // The EndEditHint part
@@ -3102,7 +3102,7 @@ void QAbstractItemView::closePersistentEditor(const QModelIndex &index)
             closeEditor(editor, QAbstractItemDelegate::RevertModelCache);
         d->persistent.remove(editor);
         d->removeEditor(editor);
-        d->releaseEditor(editor);
+        d->releaseEditor(editor, index);
     }
 }
 
@@ -3314,7 +3314,7 @@ void QAbstractItemView::rowsAboutToBeRemoved(const QModelIndex &parent, int star
             QEditorInfo info = d->indexEditorHash.take(index);
             i = d->editorIndexHash.erase(i);
             if (info.widget)
-                d->releaseEditor(editor);
+                d->releaseEditor(editor, index);
         } else {
             ++i;
         }
@@ -3393,7 +3393,7 @@ void QAbstractItemViewPrivate::_q_columnsAboutToBeRemoved(const QModelIndex &par
             QEditorInfo info = indexEditorHash.take(it.value());
             it = editorIndexHash.erase(it);
             if (info.widget)
-                releaseEditor(editor);
+                releaseEditor(editor, index);
         } else {
             ++it;
         }

src/widgets/itemviews/qabstractitemview_p.h

@@ -200,13 +200,18 @@ public:
     // reimplemented in subclasses
     virtual void adjustViewOptionsForIndex(QStyleOptionViewItemV4*, const QModelIndex&) const {}
 
-    inline void releaseEditor(QWidget *editor) const {
+    inline void releaseEditor(QWidget *editor, const QModelIndex &index = QModelIndex()) const {
         if (editor) {
             QObject::disconnect(editor, SIGNAL(destroyed(QObject*)),
                                 q_func(), SLOT(editorDestroyed(QObject*)));
             editor->removeEventFilter(itemDelegate);
             editor->hide();
-            editor->deleteLater();
+            QAbstractItemDelegate *delegate = delegateForIndex(index);
+
+            if (delegate)
+                delegate->destroyEditor(editor, index);
+            else
+                editor->deleteLater();
         }
     }
 

tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp

@@ -224,16 +224,29 @@ private slots:
     void ctrlRubberbandSelection();
     void QTBUG6407_extendedSelection();
     void QTBUG6753_selectOnSelection();
+    void testDelegateDestroyEditor();
 };
 
 class MyAbstractItemDelegate : public QAbstractItemDelegate
 {
 public:
-    MyAbstractItemDelegate() : QAbstractItemDelegate() {};
+    MyAbstractItemDelegate() : QAbstractItemDelegate() { calledVirtualDtor = false; }
     void paint(QPainter *, const QStyleOptionViewItem &, const QModelIndex &) const {}
     QSize sizeHint(const QStyleOptionViewItem &, const QModelIndex &) const { return QSize(); }
-    QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &,
-                          const QModelIndex &) const { return new QWidget(parent); }
+    QWidget *createEditor(QWidget *parent, const QStyleOptionViewItem &, const QModelIndex &) const
+    {
+        openedEditor = new QWidget(parent);
+        return openedEditor;
+    }
+    void destroyEditor(QWidget *editor, const QModelIndex &index) const
+    {
+        calledVirtualDtor = true;
+        // QAbstractItemDelegate::destroyEditor(editor,index);
+        editor->deleteLater();
+    }
+
+    mutable bool calledVirtualDtor;
+    mutable QWidget *openedEditor;
 };
 
 // Testing get/set functions
@@ -1497,5 +1510,18 @@ void tst_QAbstractItemView::QTBUG6753_selectOnSelection()
     QCOMPARE(table.selectedItems().first(), table.item(item.row(), item.column()));
 }
 
+void tst_QAbstractItemView::testDelegateDestroyEditor()
+{
+    QTableWidget table(5, 5);
+    MyAbstractItemDelegate delegate;
+    table.setItemDelegate(&delegate);
+    table.edit(table.model()->index(1, 1));
+    TestView *tv = reinterpret_cast<TestView*>(&table);
+    QVERIFY(!delegate.calledVirtualDtor);
+    tv->tst_closeEditor(delegate.openedEditor, QAbstractItemDelegate::NoHint);
+    QVERIFY(delegate.calledVirtualDtor);
+}
+
+
 QTEST_MAIN(tst_QAbstractItemView)
 #include "tst_qabstractitemview.moc"

tests/manual/widgets/itemviews/delegate/example.cpp

@@ -0,0 +1,86 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Thorbjørn Lund Martsum - tmartsum[at]gmail.com
+** Contact: http://www.qt-project.org/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** GNU Lesser General Public License Usage
+** This file may be used under the terms of the GNU Lesser General Public
+** License version 2.1 as published by the Free Software Foundation and
+** appearing in the file LICENSE.LGPL included in the packaging of this
+** file. Please review the following information to ensure the GNU Lesser
+** General Public License version 2.1 requirements will be met:
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights. These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU General
+** Public License version 3.0 as published by the Free Software Foundation
+** and appearing in the file LICENSE.GPL included in the packaging of this
+** file. Please review the following information to ensure the GNU General
+** Public License version 3.0 requirements will be met:
+** http://www.gnu.org/copyleft/gpl.html.
+**
+** Other Usage
+** Alternatively, this file may be used in accordance with the terms and
+** conditions contained in a signed written agreement between you and Nokia.
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtWidgets/QtWidgets>
+
+class ExampleEditor : public QLineEdit
+{
+public:
+    ExampleEditor(QWidget *parent = 0):QLineEdit(parent) { qDebug() << "ctor"; }
+    ~ExampleEditor() { QApplication::instance()->quit(); }
+};
+
+class ExampleDelegate : public QItemDelegate
+{
+public:
+    ExampleDelegate():QItemDelegate() { m_editor = new ExampleEditor(0); }
+protected:
+    QWidget* createEditor(QWidget *p, const QStyleOptionViewItem &o, const QModelIndex &) const
+    {
+        m_editor->setParent(p);
+        m_editor->setGeometry(o.rect);
+        return m_editor;
+    }
+    void destroyEditor(QWidget *editor, const QModelIndex &) const
+    {
+        editor->setParent(0);
+        qDebug() << "intercepted destroy :)";
+    }
+
+    // Avoid setting data - and therefore show that the editor keeps its state.
+    void setEditorData(QWidget*, const QModelIndex &) const { }
+
+    ~ExampleDelegate() { delete m_editor; }
+    mutable ExampleEditor *m_editor;
+};
+
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+    QTableView tv;
+    QStandardItemModel m;
+    m.setRowCount(4);
+    m.setColumnCount(2);
+    tv.setModel(&m);
+    tv.show();
+    tv.setItemDelegate(new ExampleDelegate());
+    app.exec();
+}

tests/manual/widgets/itemviews/delegate/example.pro

@@ -0,0 +1,2 @@
+TEMPLATE = app
+SOURCES=example.cpp