Text ------widget树由两个widget:Center(及其子widget)和Text组成

import 'package:flutter/material.dart';

void main() => runApp(new Center(
        child: new Text(
      'Hello, world!',
      textDirection: TextDirection.ltr,
      textAlign: TextAlign.center,
      maxLines: 1,
      overflow: TextOverflow.ellipsis,
      style: TextStyle(fontSize: 80.0, color: Colors.yellow),
    )));