当我使用 onDelete() 方法删除小部件时可能会出现什么问题

下面是它的工作原理：

错误是当我从中间或第一个开始删除表单时，据我了解，首先单击的表单没有被删除，我应该正确写什么？

这是我的代码：

import 'package:flutter/material.dart';
import 'data.dart';

class FormData extends StatefulWidget {
  @override
  _FormDataState createState() => _FormDataState();
}

class _FormDataState extends State<FormData> {
  List<Data> _data = [];
  List<Widget> _children = [];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('AddPage'),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.save),
            onPressed: () {},
          )
        ],
      ),
      body: SingleChildScrollView(
        child: Center(
          child: Column(
            children: <Widget>[
              Container(
                child: _children.length <= 0
                    ? Text(
                        'tap [+] button for add',
                        style: TextStyle(color: Colors.yellow, fontSize: 18.0),
                      )
                    : Column(
                        children: _children,
                      ),
              ),
              Container(
                child: RaisedButton(
                  child: Icon(Icons.add),
                  onPressed: () => onAddForm(_data.length),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }
    void onAddForm(int keyValue) {
    setState(() {
      _data.add(Data());
    });
    _children = List.from(_children)
      ..add(Card(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            Expanded(
              flex: 85,
              child: Column(
                children: <Widget>[
                  TextField(
                    style: TextStyle(color: Colors.lime[600]),
                    onChanged: (val) {
                      onChangedName(keyValue, val);
                    },
                    decoration: InputDecoration(
                        hintText: 'name',
                        hintStyle: TextStyle(color: Colors.lime[900])),
                  ),
                  TextField(
                    keyboardType: TextInputType.number,
                    onChanged: (val) {
                      onChangedNumber(keyValue, val);
                    },
                    decoration: InputDecoration(
                      hintText: 'phoneNumber',
                      hintStyle: TextStyle(color: Colors.grey)
                      ),
                  )
                ],
              ),
            ),
            Expanded(
              flex: 15,
              child: FlatButton(
                child: Stack(
                  children: <Widget>[
                    Icon(Icons.delete, size: 28,),
                    Positioned(
                      top: -20,
                      right: -15,
                      child: CircleAvatar(
                        radius: 12,
                        backgroundColor: Colors.red,
                        child: Text(
                          '$keyValue',
                          style: TextStyle(color: Colors.white),
                        ),
                      ),
                    )
                  ],
                  overflow: Overflow.visible,
                ),
                onPressed: ()=>onDelete(keyValue),
              ),
            )
          ],
        ),
      ));
  }

  void onDelete(int index) {
    setState(() {
      _data.removeAt(index);
      _children.removeAt(index);
    });
    print(_data);
  }

  onChangedName(int index, String record) {
    setState(() {
      _data[index].phoneNumber = record;
    });
  }

  onChangedNumber(int index, String record) {
    setState(() {
      _data[index].phoneNumber = record;
    });
  }
}