ScrollBehaviors now allow or disallow scrolling speeds to be affected by the number of pointers on the screen.ScrollBehavior.multitouchDragStrategy, by default, prevents multiple pointers interacting wih the scrollable at the same time from affecting the speed of scrolling.

Prior to this change, for each pointer dragging aScrollable widget, the scroll speed would increase. This did not match platform expectations when interacting with Flutter applications.

Now, the inheritedScrollBehavior manages how multiple pointers affect scrolling widgets as specified byScrollBehavior.multitouchDragStrategy. This enum,MultitouchDragStrategy, can also be configured for the prior behavior.

This change fixed the unexpected ability to increase scroll speeds by dragging with more than one finger.

If you have relied on the previous behavior in your application, there are several ways to control and configure this feature.

• ExtendScrollBehavior,MaterialScrollBehavior, orCupertinoScrollBehavior to modify the default behavior, overridingScrollBehavior.multitouchDragStrategy.

  • With your ownScrollBehavior, you can apply it app-wide by settingMaterialApp.scrollBehavior orCupertinoApp.scrollBehavior.
  • Or, if you wish to only apply it to specific widgets, add aScrollConfiguration above the widget in question with your customScrollBehavior.

Your scrollable widgets then inherit and reflect this behavior.

• Instead of creating your ownScrollBehavior, another option for changing the default behavior is to copy the existingScrollBehavior, and set differentmultitouchDragStrategy.
  • Create aScrollConfiguration in your widget tree, and provide a modified copy of the existingScrollBehavior in the current context usingcopyWith.

To accommodate the new configurationDragGestureRecognizer was updated to supportMultitouchDragStrategy as well in other dragging contexts.

Code before migration:

MaterialApp(// ...);

Code after migration:

classMyCustomScrollBehaviorextendsMaterialScrollBehavior{// Override behavior methods and getters like multitouchDragStrategy@overrideMultitouchDragStrategygetMultitouchDragStrategy(BuildContextcontext)=>MultitouchDragStrategy.sumAllPointers;}​// Set ScrollBehavior for an entire application.MaterialApp(scrollBehavior:MyCustomScrollBehavior(),// ...);

Code before migration:

finalScrollControllercontroller=ScrollController();ListView.builder(controller:controller,itemBuilder:(BuildContextcontext,intindex){returnText('Item$index');},);

Code after migration:

classMyCustomScrollBehaviorextendsMaterialScrollBehavior{// Override behavior methods and getters like multitouchDragStrategy@overrideMultitouchDragStrategygetMultitouchDragStrategy(BuildContextcontext)=>MultitouchDragStrategy.sumAllPointers;}​// ScrollBehavior can be set for a specific widget.finalScrollControllercontroller=ScrollController();ScrollConfiguration(behavior:MyCustomScrollBehavior(),child:ListView.builder(controller:controller,itemBuilder:(BuildContextcontext,intindex){returnText('Item$index');},),);

Code before migration:

finalScrollControllercontroller=ScrollController();ListView.builder(controller:controller,itemBuilder:(BuildContextcontext,intindex){returnText('Item$index');},);

Code after migration:

// ScrollBehavior can be copied and adjusted.finalScrollControllercontroller=ScrollController();ScrollConfiguration(behavior:ScrollConfiguration.of(context).copyWith(multitouchDragStrategy:MultitouchDragStrategy.sumAllPointers,),child:ListView.builder(controller:controller,itemBuilder:(BuildContextcontext,intindex){returnText('Item$index');},),);

Landed in version: 3.18.0-4.0.pre
In stable release: 3.19.0

API documentation:

• ScrollConfiguration
• ScrollBehavior
• MaterialScrollBehavior
• CupertinoScrollBehavior
• MultitouchDragStrategy
• DragGestureRecognizer

Relevant issue:

• Issue #11884

Relevant PRs:

• Introduce multi-touch drag strategies for DragGestureRecognizer