How to animate expandable Flutter widget to slide it out of the screen

Question

I have two expandable buttons in a row occupied all screen width. On left button click I want left button to occupy whole screen width and right button to disappear by siding right, out of the screen. Here is what I achieved so far:

As you noticed, the right button gets squashed at the end when there is no enough space to render it. I just want it to continue moving out of the screen without changing it's width. I could achieve this by setting text one line for button, but I want the solution to work in general for all widgets (to look like there is the space to the right enough to render it).

Current solution:

import 'package:flutter/material.dart';

void main() => runApp(TestAnimation());

class TestAnimation extends StatefulWidget {
  @override
  _TestAnimationState createState() => _TestAnimationState();
}

class _TestAnimationState extends State<TestAnimation> with SingleTickerProviderStateMixin {
  AnimationController _animationController;
  Animation _animation;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(duration: Duration(seconds: 2), vsync: this);
    _animation = IntTween(begin: 100, end: 0).animate(_animationController);
    _animation.addListener(() => setState(() {}));
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Row(
            children: <Widget>[
              Expanded(
                flex: 100,
                child: OutlineButton(
                  child: Text("Left"),
                  onPressed: () {
                    if (_animationController.value == 0.0) {
                      _animationController.forward();
                    } else {
                      _animationController.reverse();
                    }
                  },
                ),
              ),
              Expanded(
                flex: _animation.value,
                // Uses to hide widget when flex is going to 0
                child: SizedBox(
                  width: 0,
                  child: OutlineButton(
                    child: Text(
                      "Right",
                    ),
                    onPressed: () {},
                  ),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

UPDATE: Other way would to define TextOverflow for Text Widget.

Expanded(
                flex: _animation.value,
                // Uses to hide widget when flex is going to 0
                child: SizedBox(
                  width: 0.0,
                  child: OutlineButton(
                    child: Text(
                      "Right",
                      overflow: TextOverflow.ellipsis, // Add this
                    ),
                    onPressed: () {},
                  ),
                ),
              )

This ( right button gets squashed) can be solved with help of FittedBox widget.

import 'package:flutter/material.dart';

void main() => runApp(TestAnimation());

class TestAnimation extends StatefulWidget {
  @override
  _TestAnimationState createState() => _TestAnimationState();
}

class _TestAnimationState extends State<TestAnimation> with SingleTickerProviderStateMixin {
  AnimationController _animationController;
  Animation _animation;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(duration: Duration(seconds: 2), vsync: this);
    _animation = IntTween(begin: 100, end: 0).animate(_animationController);
    _animation.addListener(() => setState(() {}));
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Row(
            children: <Widget>[
              Expanded(
                flex: 100,
                child: OutlineButton(
                  child: Text("Left"),
                  onPressed: () {
                    if (_animationController.value == 0.0) {
                      _animationController.forward();
                    } else {
                      _animationController.reverse();
                    }
                  },
                ),
              ),
              Expanded(
                flex: _animation.value,
                // Uses to hide widget when flex is going to 0
                child: SizedBox(
                  width: 0.0,
                  child: OutlineButton(
                    child: FittedBox(    //Add this
                      child: Text(
                        "Right",
                      ),
                    ),
                    onPressed: () {},
                  ),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
}

output: