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>

2 files changed, 2 insertions, 2 deletions

diff --git a/examples/widgets/draganddrop/fridgemagnets/dragwidget.cpp b/examples/widgets/draganddrop/fridgemagnets/dragwidget.cpp
index b185b2900d..451b53f623 100644
--- a/examples/widgets/draganddrop/fridgemagnets/dragwidget.cpp
+++ b/examples/widgets/draganddrop/fridgemagnets/dragwidget.cpp
@@ -167,7 +167,7 @@ void DragWidget::dropEvent(QDropEvent *event)
                              QString::SkipEmptyParts);
         QPoint position = event->pos();
 
-        foreach (const QString &piece, pieces) {
+        for (const QString &piece : pieces) {
             DragLabel *newLabel = new DragLabel(piece, this);
             newLabel->move(position);
             newLabel->show();
diff --git a/examples/widgets/draganddrop/fridgemagnets/dragwidget.h b/examples/widgets/draganddrop/fridgemagnets/dragwidget.h
index 104e500134..ff513a33d8 100644
--- a/examples/widgets/draganddrop/fridgemagnets/dragwidget.h
+++ b/examples/widgets/draganddrop/fridgemagnets/dragwidget.h
@@ -62,7 +62,7 @@ QT_END_NAMESPACE
 class DragWidget : public QWidget
 {
 public:
-    DragWidget(QWidget *parent = 0);
+    explicit DragWidget(QWidget *parent = nullptr);
 
 protected:
     void dragEnterEvent(QDragEnterEvent *event) override;