Also, introduce Colors and Typography to hold the material colors and the
typography declarations. Previously we expected clients of these libraries to
import them into a namespace, but that doesn't play nice with re-exporting them
from material.dart.
Move the animation libraries into src/animation and change importers to use
package:sky/animation.dart. Also, move scheduler.dart into the animation
library so that the animation library can be self-contained.
Add a way of having keys based on numeric types or DateTimes by having a ValueKey<T> class.
Remove the redundant ways of declaring things, except for leaving one shorthand -- you can say `new Key(s)` instead of `new ValueKey<String>(s)`.
Adds itemsWrap:bool (default false) to ScrollableList and PageableList. If itemsWrap is true then scrolling past the last item wraps around to the first. Similarly, scrolling before the first item wraps around to the last.
Added abstract ExtentScrollBehavior of ScrollBehavior. Renamed fields called contentsExtents to contentExtent, containerExtents to containerExtent, contentSize to contentExtent, etc.
BoundedBehavior is now a subclass of ExtentScrollBehavior.
Added UnboundedBehavior subclass of ExtentScrollBehvaior; contentExtent and maxScrollOffset are double.INFINITY, minScrollExtent is double.NEGATIVE_INFINITY.
Changed the pageable_list.dart example: tapping on the toolbar changes
the scroll direction. This exposed some problems:
- Scrollable.syncFields() didn't update scrollDirection
- Viewport updated its RenderObject fields in the wrong order
- FixedHeightScrollable scrollDirection changes didn't update the scrollBehavior
There may be similar problems with VariableHeightList and ScrollableViewport.
I will fix those in a separate CL.
