Search SearchDelegate

showSuggestions(context)：这个方法显示建议的搜索内容，也就是Widget buildSuggestions(BuildContext context)方法的的调用；

2

Widget buildLeading(BuildContext context):这个方法返回一个控件，显示为搜索框左侧的按钮，一般设置为返回，这里返回一个具有动态效果的返回按钮：

Widget buildSuggestions(BuildContext context):这个方法返回一个控件，显示为搜索内容区域的建议内容。buildResults方法，是搜到到内容后的展现，

showSearch(context: context, delegate: searchBarDelegate()):跳转到搜索界面。

const searchList = ["益阳", "长沙", "衡阳", "郴州", "宁乡"];

const recentSuggest = ["益阳", "长沙"];

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: 'Flutter Demo', theme: ThemeData.light(), home: SearchBarDemo());
  }
}

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

class SearchBarDemo extends StatefulWidget {
  _SearchBarDemoState createState() => _SearchBarDemoState();
}

class _SearchBarDemoState extends State {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: Text('SearchBarDemo'), actions: [
      IconButton(
          icon: Icon(Icons.search),
          onPressed: () {
            showSearch(context: context, delegate: searchBarDelegate());
          }
          // showSearch(context:context,delegate: searchBarDelegate()),
          ),
    ]));
  }
}

class searchBarDelegate extends SearchDelegate {
  @override
  List buildActions(BuildContext context) {
    return [
      IconButton(
        icon: Icon(Icons.clear),
        onPressed: () => query = "",
      )
    ];
  }

  @override
  Widget buildLeading(BuildContext context) {
    return IconButton(
        icon: AnimatedIcon(
            icon: AnimatedIcons.menu_arrow, progress: transitionAnimation),
        onPressed: () => close(context, ''));
  }

  @override
  Widget buildResults(BuildContext context) {
    return Container(
      width: 100.0,
      height: 100.0,
      child: Card(
        color: Colors.redAccent,
        child: Center(
          child: Text(query),
        ),
      ),
    );
  }

  @override
  Widget buildSuggestions(BuildContext context) {
    final suggestionList = query.isEmpty
        ? recentSuggest
        : searchList.where((input) => input.startsWith(query)).toList();
    return ListView.builder(
        itemCount: suggestionList.length,
        itemBuilder: (context, index) => ListTile(
              title: RichText(
                  text: TextSpan(
                      text: suggestionList[index].substring(0, query.length),
                      style: TextStyle(
                          color: Colors.black, fontWeight: FontWeight.bold),
                      children: [
                    TextSpan(
                        text: suggestionList[index].substring(query.length),
                        style: TextStyle(color: Colors.grey))
                  ])),
            ));
  }
}