Added callbacks to DragAndDropContainer to be told when drag operations begin/end.

modules/juce_gui_basics/mouse/juce_DragAndDropContainer.cpp

@@ -69,6 +69,8 @@ public:
                 if (current->isInterestedInDragSource (sourceDetails))
                     current->itemDragExit (sourceDetails);
         }
+
+        owner.dragOperationEnded();
     }
 
     void paint (Graphics& g) override
@@ -164,14 +166,14 @@ public:
 
         if (sourceDetails.sourceComponent == nullptr)
         {
-            delete this;
+            deleteSelf();
         }
         else if (! isMouseButtonDownAnywhere())
         {
             if (mouseDragSource != nullptr)
                 mouseDragSource->removeMouseListener (this);
 
-            delete this;
+            deleteSelf();
         }
     }
 
@@ -180,7 +182,7 @@ public:
         if (key == KeyPress::escapeKey)
         {
             dismissWithAnimation (true);
-            delete this;
+            deleteSelf();
             return true;
         }
 
@@ -311,12 +313,17 @@ private:
                       && ModifierKeys::getCurrentModifiersRealtime().isAnyMouseButtonDown())
                 {
                     (new ExternalDragAndDropMessage (files, canMoveFiles))->post();
-                    delete this;
+                    deleteSelf();
                 }
             }
         }
     }
 
+    void deleteSelf()
+    {
+        delete this;
+    }
+
     void dismissWithAnimation (const bool shouldSnapBack)
     {
         setVisible (true);
@@ -449,6 +456,8 @@ void DragAndDropContainer::startDragging (const var& sourceDescription,
         if (ComponentPeer* const peer = dragImageComponent->getPeer())
             peer->performAnyPendingRepaintsNow();
        #endif
+
+        dragOperationStarted();
     }
 }
 
@@ -473,6 +482,9 @@ bool DragAndDropContainer::shouldDropFilesWhenDraggedExternally (const DragAndDr
     return false;
 }
 
+void DragAndDropContainer::dragOperationStarted()  {}
+void DragAndDropContainer::dragOperationEnded()    {}
+
 //==============================================================================
 DragAndDropTarget::SourceDetails::SourceDetails (const var& desc, Component* comp, Point<int> pos) noexcept
     : description (desc),

modules/juce_gui_basics/mouse/juce_DragAndDropContainer.h

@@ -165,6 +165,12 @@ protected:
     virtual bool shouldDropFilesWhenDraggedExternally (const DragAndDropTarget::SourceDetails& sourceDetails,
                                                        StringArray& files, bool& canMoveFiles);
 
+    /** Subclasses can override this to be told when a drag starts. */
+    virtual void dragOperationStarted();
+
+    /** Subclasses can override this to be told when a drag finishes. */
+    virtual void dragOperationEnded();
+
 private:
     //==============================================================================
     class DragImageComponent;