animating_layout_manager.h | Explore in Territory

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_VIEWS_LAYOUT_ANIMATING_LAYOUT_MANAGER_H_
#define UI_VIEWS_LAYOUT_ANIMATING_LAYOUT_MANAGER_H_

#include <memory>
#include <utility>
#include <vector>

#include "base/memory/raw_ptr.h"
#include "base/observer_list.h"
#include "base/time/time.h"
#include "ui/gfx/animation/tween.h"
#include "ui/views/layout/flex_layout_types.h"
#include "ui/views/layout/layout_manager_base.h"
#include "ui/views/views_export.h"

namespace gfx {
class AnimationContainer;
}  // namespace gfx

namespace views {

// Layout manager which explicitly animates its child views and/or its preferred
// size when the target layout changes (the target layout being provided by a
// separate, non-animating layout manager; typically a FlexLayout).
//
// For example, consider a view in which multiple buttons can be displayed
// depending on context, in a horizontal row. When we add a button, we want all
// the buttons to the left to slide over and the new button to appear in the
// gap:
//     | [a] [b] [c] |
//    | [a] [b]  [c] |
//   | [a] [b] . [c] |
//  | [a] [b] .. [c] |
// | [a] [b] [x] [c] |
//
// Without AnimatingLayoutManager you would have to explicitly animate the
// bounds of the host view and the layout elements each frame, calculating which
// go where. With AnimatingLayout you create a single declarative layout for the
// whole thing and just insert the button where you want it. Here's the setup:
//
//   auto* animating_layout = button_container->SetLayoutManager(
//       std::make_unique<AnimatingLayoutManager>());
//   animating_layout->SetBoundsAnimationMode(
//       AnimatingLayoutManager::BoundsAnimationMode::kAnimateMainAxis);
//   auto* flex_layout = animating_layout->SetTargetLayoutManager(
//       std::make_unique<FlexLayout>());
//   flex_layout->SetOrientation(LayoutOrientation::kHorizontal)
//              .SetCollapseMargins(true)
//              .SetDefault(kMarginsKey, gfx::Insets(5));
//
// Now, when you want to add (or remove) a button and animate, you just call:
//
//   button_container->AddChildViewAt(button, position);
//   button_container->RemoveChildView(button);
//
// The bounds of |button_container| will then animate appropriately and |button|
// will either appear or disappear in the appropriate location.
//
// Note that under normal operation, any changes made to the host view before
// being added to a widget will not result in animation. If initial setup of the
// host view happens after being added to a widget, you can call ResetLayout()
// to prevent changes made during setup from animating.
class VIEWS_EXPORT AnimatingLayoutManager : public LayoutManagerBase { … };

}  // namespace views

#endif  // UI_VIEWS_LAYOUT_ANIMATING_LAYOUT_MANAGER_H_
chromium/ui/views/layout/animating_layout_manager.h
