Fixed a bug in an Objective-C drag and drop helper class

modules/juce_gui_basics/mouse/juce_DragAndDropContainer.h

@@ -130,8 +130,8 @@ public:
         @param files            a list of filenames to drag
         @param canMoveFiles     if true, the app that receives the files is allowed to move the files to a new location
                                 (if this is appropriate). If false, the receiver is expected to make a copy of them.
-        @returns        true if the files were successfully dropped somewhere, or false if it
-                        was interrupted
+        @returns                true if the files were successfully dropped somewhere, or false if it
+                                was interrupted
         @see performExternalDragDropOfText
     */
     static bool performExternalDragDropOfFiles (const StringArray& files, bool canMoveFiles);

modules/juce_gui_basics/native/juce_mac_Windowing.mm

@@ -24,20 +24,7 @@
 
 } // namespace juce
 
-@interface NSDraggingSourceHelper : NSObject <NSDraggingSource>
-{
-}
-@end
-
-@implementation NSDraggingSourceHelper
-
--(NSDragOperation) draggingSession: (NSDraggingSession *)session sourceOperationMaskForDraggingContext: (NSDraggingContext)context
-{
-    juce::ignoreUnused (session, context);
-    return NSDragOperationCopy;
-}
-
-@end
+#include "../../juce_core/native/juce_osx_ObjCHelpers.h"
 
 namespace juce {
 
@@ -250,6 +237,26 @@ bool DragAndDropContainer::performExternalDragDropOfText (const String& text)
     return false;
 }
 
+class NSDraggingSourceHelper   : public ObjCClass <NSObject <NSDraggingSource>>
+{
+public:
+    NSDraggingSourceHelper()
+        : ObjCClass <NSObject <NSDraggingSource>> ("JUCENSDraggingSourceHelper_")
+    {
+        addMethod (@selector (draggingSession:sourceOperationMaskForDraggingContext:), sourceOperationMaskForDraggingContext, "c@:@@");
+
+        registerClass();
+    }
+
+private:
+    static NSDragOperation sourceOperationMaskForDraggingContext (id, SEL, NSDraggingSession*, NSDraggingContext)
+    {
+        return NSDragOperationCopy;
+    }
+};
+
+static NSDraggingSourceHelper draggingSourceHelper;
+
 bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& files, bool /*canMoveFiles*/)
 {
     if (files.isEmpty())
@@ -279,7 +286,7 @@ bool DragAndDropContainer::performExternalDragDropOfFiles (const StringArray& fi
                     [dragItem release];
                 }
 
-                auto* helper = [[NSDraggingSourceHelper alloc] autorelease];
+                auto* helper = [draggingSourceHelper.createInstance() autorelease];
 
                 if (! [view beginDraggingSessionWithItems: dragItems
                                                     event: event