Flutter PageView：禁用左侧或右侧滚动 [英] Flutter PageView: Disable left or right side scrolling

问题描述

我有一个PageView，如何禁用向左或向右滚动。我知道使用 NeverScrollableScrollPhysics 可以禁用滚动，但是如何禁用滚动

I have a PageView, how can I disable the left or right scrolling. I know by using NeverScrollableScrollPhysics we can disable the scrolling but how to disable the scrolling in one direction.

推荐答案

您可以创建自己的 ScrollPhysics 来只允许转到右边：

You can create your own ScrollPhysics to allow only go to the right:

            class CustomScrollPhysics extends ScrollPhysics {
              CustomScrollPhysics({ScrollPhysics parent}) : super(parent: parent);

              bool isGoingLeft = false;

              @override
              CustomScrollPhysics applyTo(ScrollPhysics ancestor) {
                return CustomScrollPhysics(parent: buildParent(ancestor));
              }

              @override
              double applyPhysicsToUserOffset(ScrollMetrics position, double offset) {
                isGoingLeft = offset.sign < 0;
                return offset;
              }

              @override
              double applyBoundaryConditions(ScrollMetrics position, double value) {
                //print("applyBoundaryConditions");
                assert(() {
                  if (value == position.pixels) {
                    throw FlutterError(
                        '$runtimeType.applyBoundaryConditions() was called redundantly.\n'
                        'The proposed new position, $value, is exactly equal to the current position of the '
                        'given ${position.runtimeType}, ${position.pixels}.\n'
                        'The applyBoundaryConditions method should only be called when the value is '
                        'going to actually change the pixels, otherwise it is redundant.\n'
                        'The physics object in question was:\n'
                        '  $this\n'
                        'The position object in question was:\n'
                        '  $position\n');
                  }
                  return true;
                }());
                if (value < position.pixels && position.pixels <= position.minScrollExtent)
                  return value - position.pixels;
                if (position.maxScrollExtent <= position.pixels && position.pixels < value)
                  // overscroll
                  return value - position.pixels;
                if (value < position.minScrollExtent &&
                    position.minScrollExtent < position.pixels) // hit top edge

                  return value - position.minScrollExtent;

                if (position.pixels < position.maxScrollExtent &&
                    position.maxScrollExtent < value) // hit bottom edge
                  return value - position.maxScrollExtent;

                if (!isGoingLeft) {
                  return value - position.pixels;
                }
                return 0.0;
              }
            }

用法：

            @override
              Widget build(BuildContext context) {
                return Scaffold(
                    appBar: AppBar(),
                    body: PageView.builder(
                      itemCount: 4,
                      physics: CustomScrollPhysics(),
                      itemBuilder: (context, index) => Center(
                            child: Text("Item $index"),
                          ),
                    ));
              }

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