* migrate widget to nullsafety
* remove double blank line after license
* address review comments in actions.dart
* nullable ObjectKey.value
* use local variable oldElement
* make State.build non-nullable
* make State.context non-nullable
* newline at eof
* make ProxyWidget.child non-nullable
* make _InactiveElements.debugContains non-nullable
* make Element.depth non-nullable
* make ProxyElement.build non-nullable
* make StatefulElement.state non-nullable
* remove 'Notice that'
* avoid cast of list in RenderObjectElement.updateChildren
* make IndexedSlot.value non-nullable
* avoid cast of list in MultiChildRenderObjectElement.mount
* make some WidgetsApp parameters non-nullable
* hitTest take non-nullable position
* make ScrollableState.position non-nullable
* use _pixels instead of pixels
* make ViewportOffset.pixels non-nullable
* make param and return type of IndexedWidgetBuilder non-nullable
* unused_import
* make context param non-nullable for Builder in animated_list.dart
* make ScrollMetrics.viewportDimension non-nullable
* make ScrollMetrics.{min,max}ScrollExtent non-nullable
* make _Location.file non-nullable
* _WidgetForTypeTests.createElement throw UnimplementedError
* update _NullWidget.build error message
* make _ShortcutsState.manager non-nullable
* Fix childCount issues for NNBD
* fix childCount computation on web
* increase max value on js side to compute childCount
* make aspect parameter of dependOnInheritedWidgetOfExactType nullable
* merge has{min,max}ScrollExtent into hasScrollExtents
* update focus_manager.dart
* address review comments in icon.dart
* address review comments in image.dart
* address review comments in routes.dart
* address review comments in scroll_activity.dart
* update doc comments
* make UserScrollNotification.direction non-nullable and required
* rename hasScrollExtents to hasContentDimensions
* unnecessary late
Co-authored-by: Ian Hickson <ian@hixie.ch>
Currently the framework uses fairly large "hit slop" values to disambiguate taps from drags/pans. This makes sense on touch devices where the interaction is not very precise, on mice however it can feel as if the UI is lagging. This is immediately noticeable on our infra dashboard, where it takes almost half of a grid square of drag before the actual drag kicks in.
One potential solution is to always use smaller constants depending on whether the interaction is mouse or touch based. The only reasonable choice is to use the pointer device kind and not target platform - same platform can have different input sources. This requires exposing the pointer device kind in a few new places in several of the gesture detectors, and using the enum to compute the correct hit slop from an expanded set of constants.
This almost works, however there are a few places (notably ListViews) which uses the touch hit slop as a default value in scroll physics. It does not seem like it will be easy to disambiguate a user provided scroll physics constant from the default and/or adjust it somehow - this might require significant changes to scroll physics which I have left out of this PR.
This PR does not adjust:
kTouchSlop used in scroll_physics.dart's minFlingDistance
kTouchSlop used in PrimaryPointerGestureRecognizer/LongPressGestureRecognizer
This allows us to rationalize the nullability of some of our APIs.
Prior to this we'd end up in a situation where Container assumed that
getClipPath would be non-null but Decoration was ok with return null.
Previous benchmarks have established the performance of sync*. Additionally, why allocate a list when you don't need to? Since these APIs are private, they can be re-arranged a bit to avoid creating as many lists. Will probably not have a large effect on benchmarks
