(These are changes cherry-picked from in-flight branches since they are
more independent and could be helpful even without those changes.)
- Change RouteBuilder's signature to take a single argument in which the
other fields are placed, so that we can keep iterating on those
arguments without having to break compatibility each time. Also, this
makes defining route builders much simpler (only one argument to
ignore rather than a variable number).
- Expose the next performance to RouteBuilders, since sometimes the
route itself might not be where it's used.
- Allow BuildContext to be used to walk children, just like it can for
ancestors
- Allow BuildContext to be used to get the Widget of the current
BuildContext
- Allow StatefulComponentElement to be referenced with a type
specialisation so that you don't have to cast when you know what the
type you're dealing with actually is.
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.
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)`.
Similar to widgets.dart, rendering.dart exports the entire rendering layer.
Also, update the examples to use rendering.dart and widgets.dart. Also clean up
some exports so that the examples have more sensible imports.
Added a ScrollListener listener to Scrollable. The ScrollListener runs each time the Scrollable's scrollOffset changes. This can be used to keep overlay widgets in sync with a Scrollable below them.
Removed the Scrollable ScrollClient API. It was no longer used and was clumsy to use as a ScrollListener.
Added global function findScrollableAncestor() to scrollable.dart.
Added examples/widgets/overlay_geometry.dart. The app's Scaffold is contained by a Stack. The Stack is used to display green overlay "Markers" at the corners of the most recently selected list item and where the corresponding tap occurred. The app uses widget.localToGlobal() to compute the global overlay positions of the markers. The ScrollListener is used to keep the markers' positions up to date.
