sharedmemory example: Handle QSharedMemory::AlreadyExists by attaching

Not all platforms clean up the shared memory entries on exit, so the
example needs to handle that case, by attaching instead, as documented.

Change-Id: Ifbcf92d0fad429caf30710bd8a344831cb0d859c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

examples/corelib/ipc/sharedmemory/dialog.cpp

@@ -89,9 +89,13 @@ void Dialog::loadFromFile()
     int size = buffer.size();
 
     if (!sharedMemory.create(size)) {
-        ui.label->setText(tr("Unable to create shared memory segment: %1")
-                            .arg(sharedMemory.errorString()));
-        return;
+        if (sharedMemory.error() == QSharedMemory::AlreadyExists) {
+            sharedMemory.attach();
+        } else {
+            ui.label->setText(tr("Unable to create or attach to shared memory segment: %1")
+                                .arg(sharedMemory.errorString()));
+            return;
+        }
     }
     sharedMemory.lock();
     char *to = (char*)sharedMemory.data();

examples/widgets/dialogs/standarddialogs/main.mm

@@ -0,0 +1,47 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QApplication>
+#include <QScreen>
+#include <QStyleHints>
+#include <QTranslator>
+#include <QLocale>
+#include <QLibraryInfo>
+
+#include "dialog.h"
+
+#include <AppKit/AppKit.h>
+
+using namespace Qt::StringLiterals;
+
+int main(int argc, char *argv[])
+{
+    [NSApplication sharedApplication];
+    NSApplicationLoad();
+    NSApplicationLoad();
+    [NSApp run];
+    
+    QApplication app(argc, argv);
+    //app.setAttribute(Qt::AA_DontUseNativeDialogs);
+
+#if QT_CONFIG(translation)
+    QTranslator translator;
+    if (translator.load(QLocale::system(), u"qtbase"_s, u"_"_s,
+                        QLibraryInfo::path(QLibraryInfo::TranslationsPath))) {
+        app.installTranslator(&translator);
+    }
+#endif
+
+    QGuiApplication::setApplicationDisplayName(Dialog::tr("Standard Dialogs"));
+
+    Dialog dialog;
+    if (!QGuiApplication::styleHints()->showIsFullScreen() && !QGuiApplication::styleHints()->showIsMaximized()) {
+        const QRect availableGeometry = dialog.screen()->availableGeometry();
+        dialog.resize(availableGeometry.width() / 3, availableGeometry.height() * 2 / 3);
+        dialog.move((availableGeometry.width() - dialog.width()) / 2,
+                    (availableGeometry.height() - dialog.height()) / 2);
+    }
+    dialog.show();
+
+    return app.exec();
+}