Flutter 滚动控制器如何工作，它们如何执行

Question

Flutter ：我是 flutter 的新手，我想知道它们在幕后如何工作（当我们将滚动控制器附加到可滚动小部件时实际会发生什么。）。我阅读了文档，但我很难理解。

                  controller: ** _controller **,
                  scrollDirection: Axis.vertical,
                  child: Wrap(
                    // direction: Axis.horizontal,
                    crossAxisAlignment: WrapCrossAlignment.center,
                    spacing: 4.0,
                    runSpacing: 4.0,
                    children: *MY WIDGET*,
                  ),```

Answer 1

这是一个很好的问题，也是我很好奇的问题。如果您使用 ListView，它会子类化另一个名为 BoxScrollView 的类，而该类本身又是 ScrollView 的子类，实际上是 ScrollView如果您查看以下代码，它会保留 ScrollController 实例：

  /// {@template flutter.widgets.scroll_view.controller}
  /// An object that can be used to control the position to which this scroll
  /// view is scrolled.
  ///
  /// Must be null if [primary] is true.
  ///
  /// A [ScrollController] serves several purposes. It can be used to control
  /// the initial scroll position (see [ScrollController.initialScrollOffset]).
  /// It can be used to control whether the scroll view should automatically
  /// save and restore its scroll position in the [PageStorage] (see
  /// [ScrollController.keepScrollOffset]). It can be used to read the current
  /// scroll position (see [ScrollController.offset]), or change it (see
  /// [ScrollController.animateTo]).
  /// {@endtemplate}
  final ScrollController? controller;

如果您查看 ScrollView 的 build() 函数，您会看到这颗宝石：

  @override
  Widget build(BuildContext context) {
    final List<Widget> slivers = buildSlivers(context);
    final AxisDirection axisDirection = getDirection(context);

    final ScrollController? scrollController =
        primary ? PrimaryScrollController.of(context) : controller;
    final Scrollable scrollable = Scrollable(
      dragStartBehavior: dragStartBehavior,
      axisDirection: axisDirection,
      controller: scrollController,

你看到了将 controller 作为参数的 Scrollable 实例？

我不会粘贴更多代码，因为它可能会很长，但我建议您继续查看 Scrollablle 和 ScrollView 的源代码以获取更好地了解它们的工作原理。