flutter_picker 两列的数组方式怎么写

可以使用 `Picker()` 组件，设置 `PickerDataAdapter()` 适配器，示例代码如下：

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Picker Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Picker Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _selectedFirstIndex = 0;
  int _selectedSecondIndex = 0;

  List<String> _firstList = [
    'Option 1',
    'Option 2',
    'Option 3',
    'Option 4',
    'Option 5'
  ];

  List<String> _secondList = [
    'Suboption 1',
    'Suboption 2',
    'Suboption 3',
    'Suboption 4',
    'Suboption 5'
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            showPicker();
          },
          child: Text('Show Picker'),
        ),
      ),
    );
  }

  void showPicker() {
    Picker(
        adapter: PickerDataAdapter<String>(
          pickerdata: [
            PickerDataItem(
                text: _firstList[_selectedFirstIndex],
                children: _secondList.map((e) => PickerDataItem(text: e)).toList())
          ],
        ),
        onConfirm: (Picker picker, List value) {
          setState(() {
            _selectedFirstIndex = value[0];
            _selectedSecondIndex = value[1];
          });
        },
        selecteds: [_selectedFirstIndex, _selectedSecondIndex],
        itemExtent: 50,
        height: 200,
        cancelText: 'Cancel',
        confirmText: 'Confirm')
      ..showModal(context);
  }
}

在适配器中，我们可以通过 `PickerDataItem()` 来设置每一列的数据，使用 `children` 参数来设置第二列的数据。在 `selecteds` 参数中，我们可以指定每一列的默认选中项。在 `onConfirm` 回调中，我们可以获取到选中的项，并更新 `_selectedFirstIndex` 和 `_selectedSecondIndex` 状态。