Implement canceling of Qt-initiated drags.

- Add new virtual QPlatformDrag::cancelDrag()
  [avoiding a conflict with existing QBasicDrag::cancel()]
- Implement on Windows by returning DRAGDROP_S_CANCEL
  from IOleDropSource::QueryContinueDrag() as suggested on report.
- Implement in QBasicDrag by calling QBasicDrag::cancel()
  and quitting the event loop.
- Add new API static void QDrag::cancel() for it.

Task-number: QTBUG-47004
Change-Id: I4b4bb52e5fc226c8e04688ac1b0f9550daaf918e
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/gui/kernel/qplatformdrag.cpp b/src/gui/kernel/qplatformdrag.cpp
index d789c75d1d..11230194fc 100644
--- a/src/gui/kernel/qplatformdrag.cpp
+++ b/src/gui/kernel/qplatformdrag.cpp
@@ -155,6 +155,20 @@ Qt::DropAction QPlatformDrag::defaultAction(Qt::DropActions possibleActions,
 }
 
 /*!
+    \brief Cancels the currently active drag (only for drags of
+    the current application initiated by QPlatformDrag::drag()).
+
+    The default implementation does nothing.
+
+    \since 5.6
+ */
+
+void QPlatformDrag::cancelDrag()
+{
+    Q_UNIMPLEMENTED();
+}
+
+/*!
     \brief Called to notify QDrag about changes of the current action.
  */