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Code Explained - Tools: Question Text :
​import 'package:flutter/material.dart';

class QuestionText extends StatefulWidget {

  final String _question;
  final int _questionNumber;

  QuestionText(this._question, this._questionNumber);

  @override
  State createState() => new QuestionTextState();
}

class QuestionTextState extends State<QuestionText> with SingleTickerProviderStateMixin {

  Animation<double> _fontSizeAnimation;
  AnimationController _fontSizeAnimationController;

  @override
  void initState() {
    super.initState();
    _fontSizeAnimationController = new AnimationController(duration: new Duration(milliseconds: 500), vsync: this);
    _fontSizeAnimation = new CurvedAnimation(parent: _fontSizeAnimationController, curve: Curves.bounceOut);
    _fontSizeAnimation.addListener(() => this.setState(() {}));
    _fontSizeAnimationController.forward();

  }

  @override
  void dispose() {
    _fontSizeAnimationController.dispose();
    super.dispose();
  }

  @override
  void didUpdateWidget(QuestionText oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget._question != widget._question) {
      _fontSizeAnimationController.reset();
      _fontSizeAnimationController.forward();
    }
  }

  @override
  Widget build(BuildContext context) {
    return new Material(
      color: Colors.white,

      child: new Padding(
          padding: new EdgeInsets.symmetric(vertical: 50.0, horizontal: 30.0),
          child: new Center(
            child: new Text( widget._questionNumber.toString() + ": " + widget._question,
              style: new TextStyle(fontSize: _fontSizeAnimation.value * 20),
            ),
          )
      ),
    );
  }
}

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