页面局部更新

局部刷新 简单的例子

https://www.jianshu.com/p/e9f48141218d?tdsourcetag=s_pctim_aiomsg

void main() {
  runApp(Sample2());
}
class _Sample2State extends State<Sample2> {
  int count = 0;
  Text cacheText;
  @override
  void initState() {
    cacheText = Text(
      'cache_text',
      textDirection: TextDirection.ltr,
    );
  }
  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        RaisedButton(
          child: Text(
            '$count',
            textDirection: TextDirection.ltr,
          ),
          onPressed: () {
            print(this.widget);
            setState(() {
              count += 1;
            });
          },
        ),
        cacheText,
        Text('no_cache_text', textDirection: TextDirection.ltr),
      ],
    );
  }
}