MacViews: Implemented Drag & Drop

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 17675e73c44d8c90681eabff93600f6de4b5d1d4..f07b1eb99f6cbb1c30931fd81250811e7ae5d383 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -781,13 +781,9 @@ void Widget::RunShellDrag(View* view,
   if (!widget_deletion_observer.IsWidgetAlive())
     return;
 
-  // If the view is removed during the drag operation, dragged_view_ is set to
-  // NULL.
-  if (view && dragged_view_ == view) {
-    dragged_view_ = NULL;
-    view->OnDragDone();
-  }
-  OnDragComplete();
+#if !defined(OS_MACOSX)
+  DraggingEnded(view);

[tapted, 2016/05/26 12:31:42]

Hm - x11 spins its own runloop to "force" it to be synchronous.

e.g.

desktop_drag_drop_client_aurax11.cc has (in StartDragAndDrop(..)

  // Windows has a specific method, DoDragDrop(), which performs the entire
  // drag. We have to emulate this, so we spin off a nested runloop which will
  // track all cursor movement and reroute events to a specific handler.
  move_loop_->RunMoveLoop(
      source_window,
      cursor_manager_->GetInitializedCursor(ui::kCursorGrabbing));



RunMoveLoop calls X11WholeScreenMoveLoop which (eventually) does

  base::MessageLoopForUI* loop = base::MessageLoopForUI::current();
  base::MessageLoop::ScopedNestableTaskAllower allow_nested(loop);
  base::RunLoop run_loop;
  quit_closure_ = run_loop.QuitClosure();
  run_loop.Run();

(i.e. that last Run() line will block, running a nested message loop until the
drag is finished).

X11WholeScreenMoveLoop seems to be massively complicated though -- its git log
is huge (lots of corner cases and lifetime bugs :/ ).


Maybe an asynchronous drag and drop is a much nicer way to solve this use case.
But I'm out of my depth here :/. Presumably there's a good reason for it to be
done on x11 the way it is.

+#endif
 }
 
 void Widget::SchedulePaintInRect(const gfx::Rect& rect) {
@@ -1367,6 +1363,16 @@ void Widget::DestroyRootView() {
 
 void Widget::OnDragWillStart() {}
 
+void Widget::DraggingEnded(View* view) {
+  // If the view is removed during the drag operation, dragged_view_ is set to
+  // NULL.
+  if (view && dragged_view_ == view) {
+    dragged_view_ = NULL;
+    view->OnDragDone();
+  }
+  OnDragComplete();
+}
+
 void Widget::OnDragComplete() {}
 
 ////////////////////////////////////////////////////////////////////////////////