Created
August 20, 2019 08:31
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flutter listview pageScrollPhysics
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class CustomScrollPhysics extends ScrollPhysics { | |
final double itemDimension; | |
CustomScrollPhysics({this.itemDimension, ScrollPhysics parent}) | |
: super(parent: parent); | |
@override | |
CustomScrollPhysics applyTo(ScrollPhysics ancestor) { | |
return CustomScrollPhysics( | |
itemDimension: itemDimension, parent: buildParent(ancestor)); | |
} | |
double _getPage(ScrollPosition position) { | |
return position.pixels / itemDimension; | |
} | |
double _getPixels(double page) { | |
return page * itemDimension; | |
} | |
double _getTargetPixels( | |
ScrollPosition position, Tolerance tolerance, double velocity) { | |
double page = _getPage(position); | |
if (velocity < -tolerance.velocity) { | |
page -= 0.5; | |
} else if (velocity > tolerance.velocity) { | |
page += 0.5; | |
} | |
return _getPixels(page.roundToDouble()); | |
} | |
@override | |
Simulation createBallisticSimulation( | |
ScrollMetrics position, double velocity) { | |
// If we're out of range and not headed back in range, defer to the parent | |
// ballistics, which should put us back in range at a page boundary. | |
if ((velocity <= 0.0 && position.pixels <= position.minScrollExtent) || | |
(velocity >= 0.0 && position.pixels >= position.maxScrollExtent)) | |
return super.createBallisticSimulation(position, velocity); | |
final Tolerance tolerance = this.tolerance; | |
final double target = _getTargetPixels(position, tolerance, velocity); | |
if (target != position.pixels) | |
return ScrollSpringSimulation(spring, position.pixels, target, velocity, | |
tolerance: tolerance); | |
return null; | |
} | |
@override | |
bool get allowImplicitScrolling => false; | |
} |
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