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The scroll notification events reported for a press-drag-release gesture within a scrollable on a touch screen device begin with a `ScrollStartNotification`, followed by a series of `ScrollUpdateNotifications`, and conclude with a `ScrollEndNotification`. This protocol can be used to defer work until an interactive scroll gesture ends. For example, you might defer updating a scrollable's contents via network requests until the scroll has ended, or you might want to automatically auto-scroll at that time. In the example that follows the CustomScrollView automatically scrolls so that the last partially visible fixed-height item is completely visible when the scroll gesture ends. Many iOS applications do this kind of thing. It only makes sense to auto-scroll when the user isn't actively dragging the scrollable around. It's easy enough to do this by reacting to a ScrollEndNotifcation by auto-scrolling to align the last fixed-height list item ([source code](https://gist.github.com/HansMuller/13e2a7adadc9afb3803ba7848b20c410)). https://github.com/flutter/flutter/assets/1377460/a6e6fc77-6742-4f98-81ba-446536535f73 Dragging the scrollbar thumb in a desktop application is a similar user gesture. Currently it's not possible to defer work or auto-scroll (or whatever) while the scrollable is actively being dragged via the scrollbar thumb because each scrollbar thumb motion is mapped to a scroll start - scroll update - scroll end series of notifications. On a desktop platform, the same code behaves quite differently when the scrollbar thumb is dragged. https://github.com/flutter/flutter/assets/1377460/2593d8a3-639c-407f-80c1-6e6f67fb8c5f The stream of scroll-end events triggers auto-scrolling every time the thumb moves. From the user's perspective this feels like a losing struggle. One can also detect the beginning and end of a touch-drag by listening to the value of a ScrollPosition's `isScrollingNotifier`. This approach suffers from a similar problem: during a scrollbar thumb-drag, the `isScrollingNotifier` value isn't updated at all. This PR refactors the RawScrollbar implementation to effectively use a ScrollDragController to manage scrolls caused by dragging the scrollbar's thumb. Doing so means that dragging the thumb will produce the same notifications as dragging the scrollable on a touch device. Now desktop applications can choose to respond to scrollbar thumb drags in the same that they respond to drag scrolling on a touch screen. With the changes included here, the desktop or web version of the app works as expected, whether you're listing to scroll notifications or the scroll position's `isScrollingNotifier`. https://github.com/flutter/flutter/assets/1377460/67435c40-a866-4735-a19b-e3d68eac8139 This PR also makes the second [ScrollPosition API doc example](https://api.flutter.dev/flutter/widgets/ScrollPosition-class.html#cupertino.ScrollPosition.2) work as expected when used with the DartPad that's part of API doc page. Desktop applications also see scroll start-update-end notifications due to the mouse wheel. There is no touch screen analog for the mouse wheel, so an application that wanted to enable this kind of auto-scrolling alignment would have to include a heuristic that dealt with the sequence of small scrolls triggered by the mouse wheel. Here's an example of that: [source code](https://gist.github.com/HansMuller/ce5c474a458f5f4bcc07b0d621843165). This version of the app does not auto-align in response to small changes, wether they're triggered by dragging the scrollbar thumb of the mouse wheel. Related sliver utility PRs: https://github.com/flutter/flutter/pull/143538, https://github.com/flutter/flutter/pull/143196, https://github.com/flutter/flutter/pull/143325. |
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| actions | ||
| animated_grid | ||
| animated_list | ||
| animated_size | ||
| animated_switcher | ||
| app | ||
| app_lifecycle_listener | ||
| async | ||
| autocomplete | ||
| basic | ||
| binding | ||
| dismissible | ||
| drag_target | ||
| draggable_scrollable_sheet | ||
| editable_text | ||
| focus_manager | ||
| focus_scope | ||
| form | ||
| gesture_detector | ||
| hardware_keyboard | ||
| heroes | ||
| image | ||
| implicit_animations | ||
| inherited_model | ||
| inherited_theme | ||
| interactive_viewer | ||
| layout_builder | ||
| magnifier | ||
| navigator_pop_handler | ||
| nested_scroll_view | ||
| overflow_bar | ||
| overlay | ||
| page | ||
| page_view | ||
| pop_scope | ||
| preferred_size | ||
| restoration_properties | ||
| routes | ||
| scroll_end_notification | ||
| scroll_notification_observer | ||
| scroll_position | ||
| scroll_view | ||
| scrollbar | ||
| shared_app_data | ||
| shortcuts | ||
| sliver | ||
| sliver_fill | ||
| slotted_render_object_widget | ||
| system_context_menu | ||
| table | ||
| tap_region | ||
| text | ||
| text_magnifier | ||
| transitions | ||
| tween_animation_builder | ||
| undo_history | ||
| value_listenable_builder | ||
| navigator_utils.dart | ||