Refactoring to make adding ink drop animations easier

ui/views/scoped_target_handler.cc

Index: ui/views/scoped_target_handler.cc
diff --git a/ui/views/scoped_target_handler.cc b/ui/views/scoped_target_handler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..180a8a8779327c2ff125058a64ded9d6d0be50d7
--- /dev/null
+++ b/ui/views/scoped_target_handler.cc
@@ -0,0 +1,67 @@
+// Copyright 2015 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.
+
+#include "ui/views/scoped_target_handler.h"
+
+#include "ui/events/event.h"
+#include "ui/events/event_handler.h"
+#include "ui/events/event_target.h"
+#include "ui/views/view.h"
+
+namespace views {
+
+ScopedTargetHandler::ScopedTargetHandler(View* view,
+                                         ui::EventHandler* handler)
+    : destroyed_flag_(NULL), view_(view), new_handler_(handler){
+  original_handler_ = view_->SetTargetHandler(this);
+}
+
+ScopedTargetHandler::~ScopedTargetHandler() {
+  EventHandler* handler = view_->SetTargetHandler(original_handler_);
+  DCHECK_EQ(this, handler);
+  if (destroyed_flag_)
+    *destroyed_flag_ = true;
+}
+
+void ScopedTargetHandler::OnEvent(ui::Event* event) {
+  bool destroyed = false;
+  destroyed_flag_ = &destroyed;
+
+  if (original_handler_)
+    original_handler_->OnEvent(event);
+  else
+    EventHandler::OnEvent(event);

[sadrul, 2015/11/27 05:59:36]

I think this can now be like I suggested before:

  if (original_handler_)
    original_handler_->OnEvent(event);
  else
    view_->OnEvent(event);
  if (!destroyed)
    new_handler_->OnEvent(event);

and the On*Event() overrides can be NOTREACHED().

[varkha, 2015/11/27 15:17:03]

No, this doesn't work since view_->OnEvent will call into EventTarget::OnEvent
which returns control to ScopedTargetHandler::OnEvent and loops indefinitely. I
have also confirmed that this is caught by the unit test which crashes with call
stack overrun.

+
+  if (destroyed)
+    return;
+  destroyed_flag_ = NULL;
+
+  new_handler_->OnEvent(event);
+}
+
+void ScopedTargetHandler::OnKeyEvent(ui::KeyEvent* event) {
+  static_cast<EventHandler*>(view_)->OnKeyEvent(event);

[sadrul, 2015/11/27 05:59:36]

We shouldn't need to static_cast<>

[varkha, 2015/11/27 15:17:02]

OnXxxxEvent are protected in View and |view_| is not |this| so compiler
correctly insists on cast even though ScopedTargetHandler subclasses
EventHandler. I thought exposing those methods as public would be worse.

+}
+
+void ScopedTargetHandler::OnMouseEvent(ui::MouseEvent* event) {
+  static_cast<EventHandler*>(view_)->OnMouseEvent(event);
+}
+
+void ScopedTargetHandler::OnScrollEvent(ui::ScrollEvent* event) {
+  static_cast<EventHandler*>(view_)->OnScrollEvent(event);
+}
+
+void ScopedTargetHandler::OnTouchEvent(ui::TouchEvent* event) {
+  static_cast<EventHandler*>(view_)->OnTouchEvent(event);
+}
+
+void ScopedTargetHandler::OnGestureEvent(ui::GestureEvent* event) {
+  static_cast<EventHandler*>(view_)->OnGestureEvent(event);
+}
+
+void ScopedTargetHandler::OnCancelMode(ui::CancelModeEvent* event) {
+  static_cast<EventHandler*>(view_)->OnCancelMode(event);
+}
+
+}  // namespace views