Question

There are two types of ScrollPhysics that I want to apply to my ListView. When user reaches the bottom of the List, I want BouncingScrollPhysics() to take place, but when user reaches the top, it shouldn t bounce but rather perform ClampingScrollPhysics(). How to achieve this?

Answer 1

<>Screenshot:

/>

// create 2 instance variables
var _controller = ScrollController();
ScrollPhysics _physics = ClampingScrollPhysics();

@override
void initState() {
  super.initState();
  _controller.addListener(() {
    if (_controller.position.pixels <= 56)
      setState(() => _physics = ClampingScrollPhysics());
    else
      setState(() => _physics = BouncingScrollPhysics());
  });
}

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: ListView.builder(
      controller: _controller,
      physics: _physics,
      itemCount: 20,
      itemBuilder: (_, i) => ListTile(title: Text("Item $i")),
    ),
  );
}

Answer 2

I don t wont to reload every time it change the scroll position. And I hit upon a good one. so I leave it for future readers!

    _controller.addListener(() {
      if (_controller.position.pixels < 0) _controller.jumpTo(0);
    });

Answer 3

页: 1 履历:

我发现,在伟大的。页: 1

ListView(
  physics: const BottomModalScrollPhysics(),
  children: [...],
)

import  package:flutter/foundation.dart ;
import  package:flutter/material.dart ;
import  package:flutter/widgets.dart ;

class BottomModalScrollPhysics extends ScrollPhysics {
  /// Creates scroll physics that prevent the scroll offset from exceeding the
  /// top bound of the modal.
  const BottomModalScrollPhysics({ScrollPhysics? parent})
      : super(parent: parent);

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

  @override
  double applyBoundaryConditions(ScrollMetrics position, double value) {
    assert(() {
      if (value == position.pixels) {
        throw FlutterError.fromParts(<DiagnosticsNode>[
          ErrorSummary(
               $runtimeType.applyBoundaryConditions() was called redundantly. ),
          ErrorDescription(
               The proposed new position, $value, is exactly equal to the current position of the  
               given ${position.runtimeType}, ${position.pixels}.
 
               The applyBoundaryConditions method should only be called when the value is  
               going to actually change the pixels, otherwise it is redundant. ),
          DiagnosticsProperty<ScrollPhysics>(
               The physics object in question was , this,
              style: DiagnosticsTreeStyle.errorProperty),
          DiagnosticsProperty<ScrollMetrics>(
               The position object in question was , position,
              style: DiagnosticsTreeStyle.errorProperty)
        ]);
      }
      return true;
    }());
    final direction = position.axisDirection;
    // Normal vertical scroll
    if (direction == AxisDirection.down) {
      if (value < position.pixels &&
          position.pixels <= position.minScrollExtent) {
        // underscroll
        return value - position.pixels;
      }

      if (value < position.minScrollExtent &&
          position.minScrollExtent < position.pixels) {
        // hit top edge
        return value - position.minScrollExtent;
      }
    }
    // Reversed vertical scroll
    else if (direction == AxisDirection.up) {
      if (position.maxScrollExtent <= position.pixels &&
          position.pixels < value) {
        // overscroll
        return value - position.pixels;
      }

      if (position.pixels < position.maxScrollExtent &&
          position.maxScrollExtent < value) {
        // hit bottom edge
        return value - position.maxScrollExtent;
      }
    }
    if (parent != null) return super.applyBoundaryConditions(position, value);
    return 0.0;
  }
}

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