Add DragDropObserver to WMHelper

DragDropObserver will be used by DataDevice instances to
observe drag drop events.

Bug: b:31988797
Test: None
Change-Id: I67d15f81a59730f0d78da3d56f120a16d84a43b3
Reviewed-on: https://chromium-review.googlesource.com/578748
Commit-Queue: Daichi Hirono <hirono@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491947}

components/exo/surface.cc

@@ -28,6 +28,7 @@
 #include "components/viz/service/surfaces/surface_manager.h"
 #include "third_party/khronos/GLES2/gl2.h"
 #include "ui/aura/client/aura_constants.h"
+#include "ui/aura/client/drag_drop_delegate.h"
 #include "ui/aura/window_delegate.h"
 #include "ui/aura/window_targeter.h"
 #include "ui/base/class_property.h"
@@ -192,8 +193,8 @@ Surface::Surface() : window_(new aura::Window(new CustomWindowDelegate(this))) {
   window_->Init(ui::LAYER_NOT_DRAWN);
   window_->SetEventTargeter(base::WrapUnique(new CustomWindowTargeter));
   window_->set_owned_by_parent(false);
+  WMHelper::GetInstance()->SetDragDropDelegate(window_.get());
 }
-
 Surface::~Surface() {
   for (SurfaceObserver& observer : observers_)
     observer.OnSurfaceDestroying(this);
@@ -207,6 +208,8 @@ Surface::~Surface() {
   // that they have been cancelled.
   for (const auto& presentation_callback : pending_presentation_callbacks_)
     presentation_callback.Run(base::TimeTicks(), base::TimeDelta());
+
+  WMHelper::GetInstance()->ResetDragDropDelegate(window_.get());
 }
 
 // static

components/exo/wm_helper.cc

@@ -5,6 +5,8 @@
 #include "components/exo/wm_helper.h"
 
 #include "base/memory/ptr_util.h"
+#include "ui/aura/client/drag_drop_delegate.h"
+#include "ui/base/dragdrop/drag_drop_types.h"
 
 namespace exo {
 namespace {
@@ -86,6 +88,22 @@ void WMHelper::RemoveDisplayConfigurationObserver(
   display_config_observers_.RemoveObserver(observer);
 }
 
+void WMHelper::AddDragDropObserver(DragDropObserver* observer) {
+  drag_drop_observers_.AddObserver(observer);
+}
+
+void WMHelper::RemoveDragDropObserver(DragDropObserver* observer) {
+  drag_drop_observers_.RemoveObserver(observer);
+}
+
+void WMHelper::SetDragDropDelegate(aura::Window* window) {
+  aura::client::SetDragDropDelegate(window, this);
+}
+
+void WMHelper::ResetDragDropDelegate(aura::Window* window) {
+  aura::client::SetDragDropDelegate(window, nullptr);
+}
+
 void WMHelper::NotifyWindowActivated(aura::Window* gained_active,
                                      aura::Window* lost_active) {
   for (ActivationObserver& observer : activation_observers_)
@@ -138,4 +156,28 @@ void WMHelper::NotifyDisplayConfigurationChanged() {
     observer.OnDisplayConfigurationChanged();
 }
 
+void WMHelper::OnDragEntered(const ui::DropTargetEvent& event) {
+  for (DragDropObserver& observer : drag_drop_observers_)
+    observer.OnDragEntered(event);
+}
+
+int WMHelper::OnDragUpdated(const ui::DropTargetEvent& event) {
+  int valid_operation = ui::DragDropTypes::DRAG_NONE;
+  for (DragDropObserver& observer : drag_drop_observers_)
+    valid_operation = valid_operation | observer.OnDragUpdated(event);
+  return valid_operation;
+}
+
+void WMHelper::OnDragExited() {
+  for (DragDropObserver& observer : drag_drop_observers_)
+    observer.OnDragExited();
+}
+
+int WMHelper::OnPerformDrop(const ui::DropTargetEvent& event) {
+  for (DragDropObserver& observer : drag_drop_observers_)
+    observer.OnPerformDrop(event);
+  // TODO(hirono): Return the correct result instead of always returning
+  // DRAG_MOVE.
+  return ui::DragDropTypes::DRAG_MOVE;
+}
 }  // namespace exo

components/exo/wm_helper.h

@@ -5,8 +5,11 @@
 #ifndef COMPONENTS_EXO_WM_HELPER_H_
 #define COMPONENTS_EXO_WM_HELPER_H_
 
+#include <memory>
+
 #include "base/macros.h"
 #include "base/observer_list.h"
+#include "ui/aura/client/drag_drop_delegate.h"
 #include "ui/base/cursor/cursor.h"
 
 namespace aura {
@@ -20,12 +23,13 @@ class ManagedDisplayInfo;
 
 namespace ui {
 class EventHandler;
+class DropTargetEvent;
 }
 
 namespace exo {
 
 // A helper class for accessing WindowManager related features.
-class WMHelper {
+class WMHelper : public aura::client::DragDropDelegate {
  public:
   class ActivationObserver {
    public:
@@ -81,7 +85,18 @@ class WMHelper {
     virtual ~DisplayConfigurationObserver() {}
   };
 
-  virtual ~WMHelper();
+  class DragDropObserver {
+   public:
+    virtual void OnDragEntered(const ui::DropTargetEvent& event) = 0;
+    virtual int OnDragUpdated(const ui::DropTargetEvent& event) = 0;
+    virtual void OnDragExited() = 0;
+    virtual int OnPerformDrop(const ui::DropTargetEvent& event) = 0;
+
+   protected:
+    virtual ~DragDropObserver() {}
+  };
+
+  ~WMHelper() override;
 
   static void SetInstance(WMHelper* helper);
   static WMHelper* GetInstance();
@@ -100,6 +115,10 @@ class WMHelper {
   void AddDisplayConfigurationObserver(DisplayConfigurationObserver* observer);
   void RemoveDisplayConfigurationObserver(
       DisplayConfigurationObserver* observer);
+  void AddDragDropObserver(DragDropObserver* observer);
+  void RemoveDragDropObserver(DragDropObserver* observer);
+  void SetDragDropDelegate(aura::Window*);
+  void ResetDragDropDelegate(aura::Window*);
 
   virtual const display::ManagedDisplayInfo& GetDisplayInfo(
       int64_t display_id) const = 0;
@@ -115,6 +134,12 @@ class WMHelper {
   virtual void RemovePostTargetHandler(ui::EventHandler* handler) = 0;
   virtual bool IsTabletModeWindowManagerEnabled() const = 0;
 
+  // Overridden from aura::client::DragDropDelegate:
+  void OnDragEntered(const ui::DropTargetEvent& event) override;
+  int OnDragUpdated(const ui::DropTargetEvent& event) override;
+  void OnDragExited() override;
+  int OnPerformDrop(const ui::DropTargetEvent& event) override;
+
  protected:
   WMHelper();
 
@@ -138,6 +163,7 @@ class WMHelper {
   base::ObserverList<TabletModeObserver> tablet_mode_observers_;
   base::ObserverList<InputDeviceEventObserver> input_device_event_observers_;
   base::ObserverList<DisplayConfigurationObserver> display_config_observers_;
+  base::ObserverList<DragDropObserver> drag_drop_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WMHelper);
 };