My first animated text with Flutter. This is using a very early version of Flutter. This probably won't work by the time you stumble across this code. :)

animated_text_flutter.dart

import 'package:flutter/material.dart'
    show
        BuildContext,
        Positioned,
        Stack,
        State,
        StatefulComponent,
        Text,
        Widget,
        runApp;
import 'package:flutter/scheduler.dart' show Scheduler;

// I need this to get the size of the window
import 'dart:ui' as ui;

// To minimize line length where I need to call scheduleFrameCallback,
// I made a short-hand sched here.
//
// I could have actually done, if I really wanted less code in my app:
// final onFrame = (callback(Duration d)) =>
//    Scheduler.instance.scheduleFrameCallback(callback);
final Scheduler sched = Scheduler.instance;

void main() {
  runApp(new MovingText());
}

// This is stateful because I am keeping height
// in the widget itself.
class MovingText extends StatefulComponent {
  @override
  State createState() => new MovingTextState();
}

// I have the [height] state in the widget,
// so I made this a State.
//
// I could have put height into some global
// and then I would only need a StatelessComponent.
class MovingTextState extends State {
  double height = 0.0;

  MovingTextState() {
    // kick off the animation. Is this the best place?
    // I assume so because I assume `this` is the same instance for
    // the whole app lifecycle.
    sched.scheduleFrameCallback(updatePadding);
  }

  updatePadding(_) {
    // tell the system that my state is changing, thus we need to re-render me
    setState(() {
      height++;
      // is this bad? should I cache the height? it will change when rotated
      if (height > ui.window.size.height) {
        height = 0.0;
      }
    });
    // continue the animation
    sched.scheduleFrameCallback(updatePadding);
  }

  @override
  Widget build(BuildContext context) {
    // I can only position something in a stack. Thus, here's a Stack.
    return new Stack([new Positioned(child: new Text('hi'), top: height)]);
  }
}

Comments welcome!

See https://groups.google.com/forum/#!topic/flutter-dev/8HiWiSTRax0