basic dragging support for OSX

src/OSX/Avalonia.MonoMac/DragSource.cs

@@ -0,0 +1,81 @@
+using System.Data;
+using System.Linq.Expressions;
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using System.Threading.Tasks;
+using Avalonia.Controls;
+using Avalonia.Controls.DragDrop;
+using Avalonia.Controls.Platform;
+using Avalonia.Input;
+using Avalonia.Input.Raw;
+using MonoMac.AppKit;
+using MonoMac.CoreGraphics;
+using MonoMac.Foundation;
+using MonoMac.OpenGL;
+
+namespace Avalonia.MonoMac
+{
+    public class DragSource : NSDraggingSource, IPlatformDragSource
+    {
+        class DS : NSDraggingSource
+        {
+            private readonly DragDropEffects _allowedEffects;
+            public ReplaySubject<DragDropEffects> Result { get; } = new ReplaySubject<DragDropEffects>();
+
+            public DS(DragDropEffects allowedEffects)
+            {
+                _allowedEffects = allowedEffects;
+            }
+            
+            public override bool IgnoreModifierKeysWhileDragging => false;
+            
+            public override NSDragOperation DraggingSourceOperationMaskForLocal(bool flag)
+            {
+                return DraggingInfo.ConvertDragOperation(_allowedEffects);
+            }
+            
+            public override void DraggedImageEndedAtOperation(NSImage image, CGPoint screenPoint, NSDragOperation operation)
+            {
+                Result.OnNext(DraggingInfo.ConvertDragOperation(operation));
+                Result.OnCompleted();
+            }
+        }
+
+        
+        
+        private readonly IInputManager _inputManager;
+        
+
+        public DragSource()
+        {
+            _inputManager = AvaloniaLocator.Current.GetService<IInputManager>();
+        }
+
+        private NSDraggingItem[] ConvertDraggedItems(IDataObject data)
+        {
+            NSString s = new NSString("FOOBAR");
+            NSPasteboardWriting w = new NSPasteboardWriting(s.Handle);
+            var text = new NSDraggingItem(w);
+            return new[] {text};
+        }
+        
+        
+        public async Task<DragDropEffects> DoDragDrop(IDataObject data, DragDropEffects allowedEffects)
+        {
+            // We need the TopLevelImpl + a mouse location so we just wait for the next event.
+            var mouseEv = await _inputManager.PreProcess.OfType<RawMouseEventArgs>().FirstAsync();
+            var view = ((mouseEv.Root as TopLevel)?.PlatformImpl as TopLevelImpl)?.View;
+            if (view == null)
+                return DragDropEffects.None;
+
+            // Prepare the source event:
+            var pt = view.TranslateLocalPoint(mouseEv.Position).ToMonoMacPoint();    
+            var ev = NSEvent.MouseEvent(NSEventType.LeftMouseDown, pt, 0, 0, 0, null, 0, 0, 0);
+
+            var ds = new DS(allowedEffects);
+            view.BeginDraggingSession(ConvertDraggedItems(data) ,ev, ds);
+
+            return await ds.Result;
+        }
+    }
+}

src/OSX/Avalonia.MonoMac/MonoMacPlatform.cs

@@ -35,7 +35,8 @@ namespace Avalonia.MonoMac
                 .Bind<ISystemDialogImpl>().ToSingleton<SystemDialogsImpl>()
                 .Bind<IClipboard>().ToSingleton<ClipboardImpl>()
                 .Bind<IRenderLoop>().ToConstant(s_renderLoop)
-                .Bind<IPlatformThreadingInterface>().ToConstant(PlatformThreadingInterface.Instance);
+                .Bind<IPlatformThreadingInterface>().ToConstant(PlatformThreadingInterface.Instance)
+                .Bind<IPlatformDragSource>().ToTransient<DragSource>();
         }
 
         public static void Initialize()