Flutter PageView：禁用左侧或右侧滚动

Question

我有一个 PageView，如何禁用向左或向右滚动。我知道通过使用NeverScrollableScrollPhysics我们可以禁用滚动，但如何禁用一个方向的滚动。

Answer 1

您可以创建自己的ScrollPhysics以只允许向右移动：

            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"),
                          ),
                    ));
              }

Answer 2

您还可以使用我最近编写的horizo​​ntal_blocked_scroll_physicals库，它允许您阻止左右移动。