DnD to load image file

PineapplePictures.pro

@@ -28,12 +28,14 @@ SOURCES += \
         main.cpp \
         mainwindow.cpp \
     graphicsview.cpp \
-    bottombuttongroup.cpp
+    bottombuttongroup.cpp \
+    graphicsscene.cpp
 
 HEADERS += \
         mainwindow.h \
     graphicsview.h \
-    bottombuttongroup.h
+    bottombuttongroup.h \
+    graphicsscene.h
 
 FORMS +=
 

graphicsscene.cpp

@@ -0,0 +1,34 @@
+#include "graphicsscene.h"
+
+#include <QGraphicsSceneMouseEvent>
+#include <QMimeData>
+#include <QDebug>
+#include <QGraphicsItem>
+#include <QUrl>
+
+GraphicsScene::GraphicsScene(QObject *parent)
+    : QGraphicsScene(parent)
+{
+    showText("Drag image here");
+}
+
+GraphicsScene::~GraphicsScene()
+{
+
+}
+
+void GraphicsScene::showImage(const QPixmap &pixmap)
+{
+    this->clear();
+    m_theThing = this->addPixmap(pixmap);
+    this->setSceneRect(m_theThing->boundingRect());
+}
+
+void GraphicsScene::showText(const QString &text)
+{
+    this->clear();
+    QGraphicsTextItem * textItem = this->addText(text);
+    textItem->setDefaultTextColor(QColor("White"));
+    m_theThing = textItem;
+    this->setSceneRect(m_theThing->boundingRect());
+}

graphicsscene.h

@@ -0,0 +1,20 @@
+#ifndef GRAPHICSSCENE_H
+#define GRAPHICSSCENE_H
+
+#include <QGraphicsScene>
+
+class GraphicsScene : public QGraphicsScene
+{
+    Q_OBJECT
+public:
+    GraphicsScene(QObject *parent = nullptr);
+    ~GraphicsScene();
+
+    void showImage(const QPixmap &pixmap);
+    void showText(const QString &text);
+
+private:
+    QGraphicsItem * m_theThing;
+};
+
+#endif // GRAPHICSSCENE_H

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());
+    }
+}

graphicsview.h

@@ -3,16 +3,27 @@
 
 #include <QGraphicsView>
 
+class GraphicsScene;
 class GraphicsView : public QGraphicsView
 {
 public:
     GraphicsView(QWidget *parent = nullptr);
 
+    void showImage(const QPixmap &pixmap);
+    void showText(const QString &text);
+
+    GraphicsScene * scene() const;
+    void setScene(GraphicsScene *scene);
+
 private:
     void mousePressEvent(QMouseEvent * event) override;
     void mouseMoveEvent(QMouseEvent * event) override;
     void mouseReleaseEvent(QMouseEvent * event) override;
     void wheelEvent(QWheelEvent *event) override;
+
+    void dragEnterEvent(QDragEnterEvent *event) override;
+    void dragMoveEvent(QDragMoveEvent *event) override;
+    void dropEvent(QDropEvent *event) override;
 };
 
 #endif // GRAPHICSVIEW_H

mainwindow.cpp

@@ -2,12 +2,15 @@
 
 #include "bottombuttongroup.h"
 #include "graphicsview.h"
+#include "graphicsscene.h"
 
 #include <QMouseEvent>
 #include <QMovie>
 #include <QDebug>
 #include <QGraphicsTextItem>
 #include <QApplication>
+#include <QStyle>
+#include <QScreen>
 
 #ifdef _WIN32
 #include <windows.h>
@@ -33,9 +36,7 @@ MainWindow::MainWindow(QWidget *parent) :
     connect(m_exitAnimationGroup, &QParallelAnimationGroup::finished,
             this, &QMainWindow::close);
 
-    QGraphicsScene * scene = new QGraphicsScene(this);
-    QGraphicsTextItem * textItem = scene->addText("Hello, world!");
-    textItem->setDefaultTextColor(QColor("White"));
+    GraphicsScene * scene = new GraphicsScene(this);
 
     GraphicsView * pictureView = new GraphicsView(this);
     pictureView->setScene(scene);
@@ -55,6 +56,15 @@ MainWindow::MainWindow(QWidget *parent) :
             this, &MainWindow::closeWindow);
 
     m_bottomButtonGroup = new BottomButtonGroup(this);
+
+    this->setGeometry(
+        QStyle::alignedRect(
+            Qt::LeftToRight,
+            Qt::AlignCenter,
+            this->size(),
+            qApp->screenAt(QCursor::pos())->geometry()
+        )
+    );
 }
 
 MainWindow::~MainWindow()