MacViews: Implemented Drag & Drop

ui/views/view.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #define _USE_MATH_DEFINES // For VC++ to get M_PI. This has to be first.
 
 #include "ui/views/view.h"
 
 #include <algorithm>
 #include <cmath>
@@ skipping 2394 matching lines @@
 
   // Don't attempt to start a drag while in the process of dragging. This is
   // especially important on X where we can get multiple mouse move events when
   // we start the drag.
   if (widget->dragged_view())
     return false;
 
   OSExchangeData data;
   WriteDragData(press_pt, &data);
 
+// The Native Event is required for OSX's native drag and drop. As such, it's
+// necessary to pass down the Event object.
+#if defined(OS_MACOSX)
+  data.provider().SetEvent(event);

[tapted, 2016/05/24 08:06:02]

So I'm still unsure about this. I found one place where it will come unstuck. In
a mac_views_browser build, if you go to chrome://bookmarks and dry to drag a
bookmark, you get a DCHECK failure:

[48403:1295:0524/171204:FATAL:os_exchange_data_provider_mac.mm(172)] Check
failed: event_.get().
logging::LogMessage::~LogMessage() + 35
ui::OSExchangeDataProviderMac::GetEvent() const + 328
views::DragDropClientMac::StartDragAndDrop(ui::OSExchangeData const&, gfx::Point
const&, int, ui::DragDropTypes::DragEventSource) + 196
views::NativeWidgetMac::RunShellDrag(views::View*, ui::OSExchangeData const&,
gfx::Point const&, int, ui::DragDropTypes::DragEventSource) + 109
views::Widget::RunShellDrag(views::View*, ui::OSExchangeData const&, gfx::Point
const&, int, ui::DragDropTypes::DragEventSource) + 156
chrome::DragBookmarks(Profile*, std::__1::vector<bookmarks::BookmarkNode const*,
std::__1::allocator<bookmarks::BookmarkNode const*> > const&, NSView*,
ui::DragDropTypes::DragEventSource) + 572
extensions::BookmarkManagerPrivateStartDragFunction::RunOnReady() + 1234

This RunShellDrag call is made in bookmark_drag_drop_views.cc

There is actually a Cocoa implementation too, in bookmark_drag_drop_cocoa.mm --
it does



  // Synthesize an event for dragging, since we can't be sure that
  // [NSApp currentEvent] will return a valid dragging event.
  NSWindow* window = [view window];
  NSPoint position = [window mouseLocationOutsideOfEventStream];
  NSTimeInterval event_time = [[NSApp currentEvent] timestamp];
  NSEvent* drag_event = [NSEvent mouseEventWithType:NSLeftMouseDragged
                                           location:position
                                      modifierFlags:NSLeftMouseDraggedMask
                                          timestamp:event_time
                                       windowNumber:[window windowNumber]
                                            context:nil
                                        eventNumber:0
                                         clickCount:1
                                           pressure:1.0];


Can we do something like that lower down in the mac-specific plumbing?

If we can, I think I'd prefer we do this "always" for now until it's a problem,
rather than changing the code here. i.e. always use a synthetic event for
view::DoDrag on Mac.

Otherwise, we should modify the interface of RunShellDrag so that it takes in an
Event* (which may be null, in which case we generate a synthetic event).

[spqchan, 2016/05/26 01:56:55]

Ahh, that's a really good point! I made a change so that it generates a
synthetic event instead. What do you mean by "lower down in the mac-specific
plumbing"?

+#endif
+
   // Message the RootView to do the drag and drop. That way if we're removed
   // the RootView can detect it and avoid calling us back.
   gfx::Point widget_location(event.location());
   ConvertPointToWidget(this, &widget_location);
   widget->RunShellDrag(this, data, widget_location, drag_operations, source);
   // WARNING: we may have been deleted.
   return true;
 }
 
 }  // namespace views