Scroll physics on iOS is excessively damped #32448
Description
I have a complex ListView with approximately 300 rows, and scrolling is demonstrating too much friction compared to a native list view on iOS. After some debugging, I figured out that it's because of this line in scroll_physics.dart:
The createBallisticSimulation method seems to get called several times per second during the ballistic part of scroll movements on my ListView, which I think is because the ScrollMetrics.maxScrollExtent property is changing slightly as Flutter discovers the rendered sizes of the widgets as they scroll into the viewport. However, each time it gets called, the velocity gets scaled down by 0.91, which effectively adds a lot of additional friction to the otherwise quite smooth BouncingScrollSimulation.
I've worked around the issue by making my own ScrollPhysics class which changes the constant to 1.0 (i.e. no multiplication), and it works great, but it would be nice to have it fixed in the framework.
@override
Simulation createBallisticSimulation(ScrollMetrics position, double velocity) {
final Tolerance tolerance = this.tolerance;
if (velocity.abs() >= tolerance.velocity || position.outOfRange) {
return BouncingScrollSimulation(
spring: spring,
position: position.pixels,
velocity: velocity * 0.91, // TODO(abarth): We should move this constant closer to the drag end.
leadingExtent: position.minScrollExtent,
trailingExtent: position.maxScrollExtent,
tolerance: tolerance,
);
}
return null;
}
Steps to Reproduce
Scroll any reasonably complex ListView on iOS and observe that the physics
seem to be excessively damped compared to native iOS list views.
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