Avoid crashing in the quickwidgets example after closing the subwindow

Closing the window deletes m_quickWidget; so we disable the menu items
for grabbing from it, because those cannot work. Also add asserts.

Fixes: QTBUG-120296
Pick-to: 6.5 6.2 5.15
Change-Id: I68154c2d1e4553c771815e29cbe3b095d85893f1
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit f719ee6408a92439a65e82abea4403df6a844066)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit a49d309b4acaba1dbb08ea1c554ad333b439b8cf)

1 files changed, 15 insertions, 3 deletions

diff --git a/examples/quick/quickwidgets/quickwidget/main.cpp b/examples/quick/quickwidgets/quickwidget/main.cpp
index ecac279a2f..584cecfb00 100644
--- a/examples/quick/quickwidgets/quickwidget/main.cpp
+++ b/examples/quick/quickwidgets/quickwidget/main.cpp
@@ -63,14 +63,22 @@ MainWindow::MainWindow()
     setCentralWidget(centralWidget);
 
     QMenu *fileMenu = menuBar()->addMenu(tr("&File"));
-    fileMenu->addAction(tr("Grab framebuffer"), this, &MainWindow::grabFramebuffer);
-    fileMenu->addAction(tr("Render to pixmap"), this, &MainWindow::renderToPixmap);
-    fileMenu->addAction(tr("Grab via grabToImage"), this, &MainWindow::grabToImage);
+    auto grabAction = fileMenu->addAction(tr("Grab framebuffer"), this, &MainWindow::grabFramebuffer);
+    auto renderAction = fileMenu->addAction(tr("Render to pixmap"), this, &MainWindow::renderToPixmap);
+    auto grabToImageAction = fileMenu->addAction(tr("Grab via grabToImage"), this, &MainWindow::grabToImage);
     fileMenu->addAction(tr("Quit"), qApp, &QCoreApplication::quit);
 
     QMenu *windowMenu = menuBar()->addMenu(tr("&Window"));
     windowMenu->addAction(tr("Add tab widget"), this,
                           [this, centralWidget] { createQuickWidgetsInTabs(centralWidget); });
+
+    connect(m_quickWidget, &QObject::destroyed, this,
+            [this, grabAction, renderAction, grabToImageAction] {
+                m_quickWidget = nullptr;
+                grabAction->setEnabled(false);
+                renderAction->setEnabled(false);
+                grabToImageAction->setEnabled(false);
+            });
 }
 
 void MainWindow::createQuickWidgetsInTabs(QMdiArea *mdiArea)
@@ -123,6 +131,7 @@ void MainWindow::quickWidgetStatusChanged(QQuickWidget::Status status)
 {
     if (status == QQuickWidget::Error) {
         QStringList errors;
+        Q_ASSERT(m_quickWidget);
         const auto widgetErrors = m_quickWidget->errors();
         for (const QQmlError &error : widgetErrors)
             errors.append(error.toString());
@@ -147,12 +156,14 @@ template<class T> void saveToFile(QWidget *parent, T *saveable)
 
 void MainWindow::grabFramebuffer()
 {
+    Q_ASSERT(m_quickWidget);
     QImage image = m_quickWidget->grabFramebuffer();
     saveToFile(this, &image);
 }
 
 void MainWindow::renderToPixmap()
 {
+    Q_ASSERT(m_quickWidget);
     QPixmap pixmap(m_quickWidget->size());
     m_quickWidget->render(&pixmap);
     saveToFile(this, &pixmap);
@@ -165,6 +176,7 @@ void MainWindow::grabToImage()
     fd.setDefaultSuffix("png");
     fd.selectFile("test_grabToImage.png");
     if (fd.exec() == QDialog::Accepted) {
+        Q_ASSERT(m_quickWidget);
         QMetaObject::invokeMethod(m_quickWidget->rootObject(), "performLayerBasedGrab",
                                   Q_ARG(QVariant, fd.selectedFiles().first()));
     }