DnD to load image file

graphicsview.cpp

@@ -1,8 +1,12 @@
 #include "graphicsview.h"
 
+#include "graphicsscene.h"
+
 #include <QDebug>
 #include <QMouseEvent>
 #include <QScrollBar>
+#include <QMimeData>
+#include <QImageReader>
 
 GraphicsView::GraphicsView(QWidget *parent)
     : QGraphicsView (parent)
@@ -12,6 +16,27 @@ GraphicsView::GraphicsView(QWidget *parent)
     setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
     setStyleSheet("background-color: rgba(0, 0, 0, 180);"
                   "border-radius: 3px;");
+    setAcceptDrops(true);
+}
+
+void GraphicsView::showImage(const QPixmap &pixmap)
+{
+    scene()->showImage(pixmap);
+}
+
+void GraphicsView::showText(const QString &text)
+{
+    scene()->showText(text);
+}
+
+GraphicsScene *GraphicsView::scene() const
+{
+    return qobject_cast<GraphicsScene*>(QGraphicsView::scene());
+}
+
+void GraphicsView::setScene(GraphicsScene *scene)
+{
+    return QGraphicsView::setScene(scene);
 }
 
 void GraphicsView::mousePressEvent(QMouseEvent *event)
@@ -57,3 +82,52 @@ void GraphicsView::wheelEvent(QWheelEvent *event)
         scale(0.8, 0.8);
     }
 }
+
+void GraphicsView::dragEnterEvent(QDragEnterEvent *event)
+{
+    if (event->mimeData()->hasUrls() || event->mimeData()->hasImage() || event->mimeData()->hasText()) {
+        event->acceptProposedAction();
+    } else {
+        event->ignore();
+    }
+    qDebug() << event->mimeData() << "Drag Enter Event"
+             << event->mimeData()->hasUrls() << event->mimeData()->hasImage()
+             << event->mimeData()->formats() << event->mimeData()->hasFormat("text/uri-list");
+
+    return QGraphicsView::dragEnterEvent(event);
+}
+
+void GraphicsView::dragMoveEvent(QDragMoveEvent *event)
+{
+    Q_UNUSED(event);
+    // by default, QGraphicsView/Scene will ignore the action if there are no QGraphicsItem under cursor.
+    // We actually doesn't care and would like to keep the drag event as-is, so just do nothing here.
+}
+
+void GraphicsView::dropEvent(QDropEvent *event)
+{
+    event->acceptProposedAction();
+
+    const QMimeData * mimeData = event->mimeData();
+
+    if (mimeData->hasUrls()) {
+        QUrl url(mimeData->urls().first());
+        QImageReader imageReader(url.toLocalFile());
+        QImage::Format imageFormat = imageReader.imageFormat();
+        if (imageFormat == QImage::Format_Invalid) {
+            showText("File is not a valid image");
+        } else {
+            showImage(QPixmap::fromImageReader(&imageReader));
+        }
+    } else if (mimeData->hasImage()) {
+        QImage img = qvariant_cast<QImage>(mimeData->imageData());
+        QPixmap pixmap = QPixmap::fromImage(img);
+        if (pixmap.isNull()) {
+            showText("Image data is invalid");
+        } else {
+            showImage(pixmap);
+        }
+    } else if (mimeData->hasText()) {
+        showText(mimeData->text());
+    }
+}