examples/widgets/dropdown.dart asserts on selection #397
Description
In examples/widgets/dropdown.dart when you select something from the drop-down you get:
-- EXCEPTION IN SCHEDULER CALLBACK --
Bad state: Future already completed
Stack trace:
#0 _AsyncCompleter.complete (dart:async/future_impl.dart:40)
#1 TransitionRoute._handleStatusChanged (flutter/packages/flutter/lib/src/widgets/routes.dart:86)
#2 Performance._checkStatusChanged (flutter/packages/flutter/lib/src/animation/performance.dart:288)
#3 Performance.didTick (flutter/packages/flutter/lib/src/animation/performance.dart:315)
#4 Performance._tick (flutter/packages/flutter/lib/src/animation/performance.dart:310)
#5 SimulationStepper._tick (flutter/packages/flutter/lib/src/animation/simulation_stepper.dart:103)
#6 Ticker._tick (flutter/packages/flutter/lib/src/animation/ticker.dart:67)
#7 Scheduler.invokeCallback (flutter/packages/flutter/lib/src/animation/scheduler.dart:81)
#8 Scheduler.beginFrame.<anonymous closure> (flutter/packages/flutter/lib/src/animation/scheduler.dart:62)
#9 _HashVMBase&MapMixin&&_LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:340)
#10 Scheduler.beginFrame (flutter/packages/flutter/lib/src/animation/scheduler.dart:60)
...