Revamp QtWidgets/DragAndDrop examples to C++11

Introduce nullptr and replace foreach with new C++11 range based for
loops. Minor fixups of signals, file dialog usage.

Apply the same changes to the ItemViews/puzzle example since it
shares parts of the code with DragAndDrop/puzzle. Make some
changes to both examples to that the diff of the two becomes
small for easier comparison.

Task-number: QTBUG-60635
Change-Id: I8af824229ebac24d6ec151eae92176d227695490
Reviewed-by: Venugopal Shivashankar <Venugopal.Shivashankar@qt.io>
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/examples/widgets/itemviews/puzzle/mainwindow.h b/examples/widgets/itemviews/puzzle/mainwindow.h
index 7e27dc6f3a..208d3a5281 100644
--- a/examples/widgets/itemviews/puzzle/mainwindow.h
+++ b/examples/widgets/itemviews/puzzle/mainwindow.h
@@ -65,7 +65,7 @@ class MainWindow : public QMainWindow
     Q_OBJECT
 
 public:
-    MainWindow(QWidget *parent = 0);
+    explicit MainWindow(QWidget *parent = nullptr);
 
 public slots:
     void openImage();