92f8455ff8
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.
Flutter Examples
This directory contains several examples of using Flutter. To run an example,
use flutter run inside that example's directory. See the getting started
guide to install the flutter tool.
For additional samples, see the
flutter/samples repo.
Available examples include:
-
Hello, world The hello world app is a minimal Flutter app that shows the text "Hello, world!"
-
Flutter gallery The flutter gallery app no longer lives in this repo. Please see the gallery repo.
-
Layers The layers vignettes show how to use the various layers in the Flutter framework. For details, see the layers README.
-
Platform Channel The platform channel app demonstrates how to connect a Flutter app to platform-specific APIs. For documentation, see https://flutter.dev/platform-channels/.
-
Platform Channel Swift The platform channel swift app is the same as platform channel but the iOS version is in Swift and there is no Android version.
Notes
Note on Gradle wrapper files in .gitignore:
Gradle wrapper files should normally be checked into source control. The example projects don't do that to avoid having several copies of the wrapper binary in the Flutter repo. Instead, the Gradle wrapper is injected by Flutter tooling, and the wrapper files are .gitignore'd to avoid making the Flutter repository dirty as a side effect of running the examples.