// Copyright 2016 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.

#ifndef UI_VIEWS_VIEW_OBSERVER_H_
#define UI_VIEWS_VIEW_OBSERVER_H_

#include "ui/views/views_export.h"

namespace views {

class View;
struct ViewHierarchyChangedDetails;

// ViewObserver is used to observe changes to a View. The first argument to all
// ViewObserver functions is the View the observer was added to.
class VIEWS_EXPORT ViewObserver {
 public:
  // Called when |child| is added as a child to |observed_view|.
  virtual void OnChildViewAdded(View* observed_view, View* child) {}

  // Called when |child| is removed as a child of |observed_view|.
  virtual void OnChildViewRemoved(View* observed_view, View* child) {}

  // Called when |observed_view|, an ancestor, or its Widget has its visibility
  // changed. |starting_view| is who |View::SetVisible()| was called on (or null
  // if the Widget visibility changed).
  virtual void OnViewVisibilityChanged(View* observed_view,
                                       View* starting_view) {}

  // Called from View::PreferredSizeChanged().
  virtual void OnViewPreferredSizeChanged(View* observed_view) {}

  // Called when the bounds of |observed_view| change.
  virtual void OnViewBoundsChanged(View* observed_view) {}

  // Called when the bounds of |observed_view|'s layer change.
  virtual void OnLayerTargetBoundsChanged(View* observed_view) {}

  // Called when View::ViewHierarchyChanged() is called.
  virtual void OnViewHierarchyChanged(
      View* observed_view,
      const ViewHierarchyChangedDetails& details) {}

  // Called when View::AddedToWidget() is called.
  virtual void OnViewAddedToWidget(View* observed_view) {}

  // Called when View::RemovedFromWidget() is called.
  virtual void OnViewRemovedFromWidget(View* observed_view) {}

  // Called when a child is reordered among its siblings, specifically
  // View::ReorderChildView() is called on |observed_view|.
  virtual void OnChildViewReordered(View* observed_view, View* child) {}

  // Called when the active UI theme or NativeTheme has changed for
  // |observed_view|.
  virtual void OnViewThemeChanged(View* observed_view) {}

  // Called from ~View.
  virtual void OnViewIsDeleting(View* observed_view) {}

  // Called immediately after |observed_view| has gained focus.
  virtual void OnViewFocused(View* observed_view) {}

  // Called immediately after |observed_view| has lost focus.
  virtual void OnViewBlurred(View* observed_view) {}

 protected:
  virtual ~ViewObserver() = default;
};

}  // namespace views

#endif  // UI_VIEWS_VIEW_OBSERVER_H_