flutter 选择器

Flutter中的选择器有多种实现方式，以下是其中两种常见的实现方式：

1. CupertinoPicker

CupertinoPicker是一个iOS风格的选择器，可以在Flutter中使用。使用CupertinoPicker需要引入cupertino库，示例代码如下：

import 'package:flutter/cupertino.dart';

class MyPicker extends StatefulWidget {
  @override
  _MyPickerState createState() => _MyPickerState();
}

class _MyPickerState extends State<MyPicker> {
  List<String> items = ['item1', 'item2', 'item3'];
  int currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return CupertinoPicker(
      itemExtent: 30,
      onSelectedItemChanged: (index) {
        setState(() {
          currentIndex = index;
        });
      },
      children: items.map((item) => Text(item)).toList(),
      scrollController: FixedExtentScrollController(initialItem: currentIndex),
    );
  }
}

2. DropdownButton

DropdownButton是一个下拉菜单，也可以用作选择器。示例代码如下：

import 'package:flutter/material.dart';

class MyDropdownButton extends StatefulWidget {
  @override
  _MyDropdownButtonState createState() => _MyDropdownButtonState();
}

class _MyDropdownButtonState extends State<MyDropdownButton> {
  List<String> items = ['item1', 'item2', 'item3'];
  String currentItem = 'item1';

  @override
  Widget build(BuildContext context) {
    return DropdownButton<String>(
      value: currentItem,
      onChanged: (value) {
        setState(() {
          currentItem = value;
        });
      },
      items: items.map((item) {
        return DropdownMenuItem<String>(
          value: item,
          child: Text(item),
        );
      }).toList(),
    );
  }
}