flutter SearchDelegate如何在不单击放大镜的情况下显示结果

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Custom Search Delegate'),
          actions: [
            IconButton(
              icon: Icon(Icons.search),
              onPressed: () {
                // 打开搜索界面
                showSearch(context: context, delegate: MySearchDelegate());
              },
            ),
          ],
        ),
      ),
    );
  }
}

class MySearchDelegate extends SearchDelegate<String> {
  @override
  List<Widget> buildActions(BuildContext context) {
    // 可以在这里添加一些操作按钮，例如清除搜索框内容
    return [
      IconButton(
        icon: Icon(Icons.clear),
        onPressed: () {
          query = '';
        },
      ),
    ];
  }

  @override
  Widget buildLeading(BuildContext context) {
    // 可以在这里添加一些前置操作按钮，例如返回按钮
    return IconButton(
      icon: Icon(Icons.arrow_back),
      onPressed: () {
        close(context, null);
      },
    );
  }

  @override
  Widget buildResults(BuildContext context) {
    // 当用户输入时，立即显示搜索结果
    return ListView.builder(
      itemCount: query.length == 0 ? 1 : query.length * 2,
      itemBuilder: (context, index) {
        if (query.length == 0) {
          return ListTile(
            title: Text('请输入搜索关键词'),
          );
        } else {
          return ListTile(
            title: Text('结果 $index: $query'),
          );
        }
      },
    );
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    // 这里可以返回搜索建议，但我们在这里直接显示结果
    return buildResults(context);
  }
}