Add imageSource property to attached Drag property

This property holds a URL which is loaded into a QPixmap via
QQuickPixmap, and subsequently set on the QDrag object.

This is especially important for drag and drop to external applications,
where of course a QQuickItem cannot be dragged; however, combined with
QQuickItem::grabToImage(), this change allows setting a QQuickItem's
contents as the drag pixmap.

[ChangeLog][QtQuick][Drag] Added imageSource property to attached Drag
object: this allows drag sources to specify the pixmap to be drawn next
to the mouse cursor when starting a drag and drop operation.

Task-number: QTBUG-37366
Change-Id: Ibcf1d888c525e50976a116ec743ce6fca4c31525
Reviewed-by: Michael Brasser <michael.brasser@live.com>

1 files changed, 43 insertions, 3 deletions

diff --git a/src/quick/items/qquickdrag.cpp b/src/quick/items/qquickdrag.cpp
index 4aa54b71df..76e13bc985 100644
--- a/src/quick/items/qquickdrag.cpp
+++ b/src/quick/items/qquickdrag.cpp
@@ -45,6 +45,7 @@
 #include <private/qquickitem_p.h>
 #include <QtQuick/private/qquickevents_p_p.h>
 #include <private/qquickitemchangelistener_p.h>
+#include <private/qquickpixmapcache_p.h>
 #include <private/qv8engine_p.h>
 #include <private/qv4scopedvalue_p.h>
 #include <QtCore/qmimedata.h>
@@ -110,6 +111,8 @@ public:
     bool eventQueued : 1;
     bool overrideActions : 1;
     QPointF hotSpot;
+    QUrl imageSource;
+    QQuickPixmap pixmapLoader;
     QStringList keys;
     QVariantMap externalMimeData;
     QQuickDrag::DragType dragType;
@@ -408,6 +411,43 @@ void QQuickDragAttached::setHotSpot(const QPointF &hotSpot)
 }
 
 /*!
+    \qmlattachedproperty QUrl QtQuick::Drag::imageSource
+    \since 5.8
+
+    This property holds the URL of the image which will be used to represent
+    the data during the drag and drop operation. Changing this property after
+    the drag operation has started will have no effect.
+
+    The example below uses an item's contents as a drag image:
+
+    \snippet qml/externaldrag.qml 0
+
+    \sa Item::grabToImage()
+*/
+
+QUrl QQuickDragAttached::imageSource() const
+{
+    Q_D(const QQuickDragAttached);
+    return d->imageSource;
+}
+
+void QQuickDragAttached::setImageSource(const QUrl &url)
+{
+    Q_D(QQuickDragAttached);
+    if (d->imageSource != url) {
+        d->imageSource = url;
+
+        if (url.isEmpty()) {
+            d->pixmapLoader.clear();
+        } else {
+            d->pixmapLoader.load(qmlEngine(this), url);
+        }
+
+        Q_EMIT imageSourceChanged();
+    }
+}
+
+/*!
     \qmlattachedproperty stringlist QtQuick::Drag::keys
 
     This property holds a list of keys that can be used by a DropArea to filter drag events.
@@ -726,9 +766,9 @@ Qt::DropAction QQuickDragAttachedPrivate::startDrag(Qt::DropActions supportedAct
         mimeData->setData(it.key(), it.value().toString().toUtf8());
 
     drag->setMimeData(mimeData);
-
-    // TODO: how to handle drag image?
-    // drag->setPixmap(iconPixmap);
+    if (pixmapLoader.isReady()) {
+        drag->setPixmap(QPixmap::fromImage(pixmapLoader.image()));
+    }
 
     emit q->dragStarted();