algorithm - 如何在 ListView 中显示字符串树？

Question

我有一个 Map<String, dynamic> ，其中 dynamic 是 Strings 的动态树.我需要在 ListView 中显示(或另一个允许显示树结构的小部件)字符串及其子项。每个 String 都是 ListView 的一个可折叠项(如果有子项)。例如:

Text
     text 
           text
           text
     text 
text
     text
text
text

这是树的示例代码:

void main() {
  Map<String, dynamic> joinTrees(int level, int maxLevel,
      List<List<String>> trees, Map<String, dynamic> tmpMap) {
    if (maxLevel < 0) return {};
    List<String> nodes = trees.map((tree) => tree[level]).toSet().toList();
    print(nodes);

    for (String node in nodes) {
      List<List<String>> childrenBranchs =
          trees.where((tree) => tree[level] == node).toList();
      if (childrenBranchs.length == 1 &&
          childrenBranchs[0][childrenBranchs[0].length - 1] == node) {
        print("leaf: " + node);
        tmpMap[node] = null;
      } else {
        Map<String, dynamic> childrenTree = joinTrees(
            level + 1, maxLevel, childrenBranchs, new Map<String, dynamic>());
        print("node: " + node);
        tmpMap[node] = childrenTree;
      }
    }
    return tmpMap;
  }

  List<List<String>> trees = [
    ["A", "A11", "A21"],
    ["A", "A12"],
    ["A", "A11", "A22"],
    ["B", "B11", "B21"],
    ["C"]
  ];
  int maxLength = trees
      .map((tree) => tree.length)
      .toList()
      .reduce((curr, next) => curr > next ? curr : next);
  int maxLevel = maxLength - 1;

  print(trees);
  print(maxLength);
  Map<String, dynamic> joinedTree =
      joinTrees(0, maxLevel, trees, new Map<String, dynamic>());
  print(joinedTree);
}

这是 joinedTree 的输出:

{
 A: 
    {
     A11: 
          {
           A21: null, 
           A22: null
          }, 
     A12: null
    }, 
 B: 
    {
     B11: 
         {
           B21: null
         }
    }, 
 C: null

}

Answer 1

如果你的树是这样的，详细的Entry类请引用完整代码

final List<Entry> data = <Entry>[
  Entry(
    'A',
    <Entry>[
      Entry(
        'A11',
        <Entry>[
          Entry('A21'),
          Entry('A22'),
        ],
      ),
      Entry('A12'),
    ],
  ),
  Entry(
    'B',
    <Entry>[
      Entry(
        'B11',
        <Entry>[
          Entry('B21'),
        ],
      ),
    ],
  ),
  Entry(
    'C',
  ),
];

在 ListView.builder 中，构建项目

Widget _buildTiles(Entry root) {
    if (root.children.isEmpty) {
      return Padding(
        padding: const EdgeInsets.only(left: 10.0),
        child: ListTile(title: Text(root.title)),
      );
    }
    return Padding(
      padding: const EdgeInsets.only(left: 10.0),
      child: ExpansionTile(
        key: PageStorageKey<Entry>(root),
        title: Text(root.title),
        children: root.children.map(_buildTiles).toList(),
      ),
    );
  }

完整代码

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: ExpansionTileSample(),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

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

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class ExpansionTileSample extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('ExpansionTile'),
        ),
        body: ListView.builder(
          itemBuilder: (BuildContext context, int index) =>
              EntryItem(data[index]),
          itemCount: data.length,
        ),
      ),
    );
  }
}

// One entry in the multilevel list displayed by this app.
class Entry {
  Entry(this.title, [this.children = const <Entry>[]]);

  final String title;
  final List<Entry> children;
}

// The entire multilevel list displayed by this app.
final List<Entry> data = <Entry>[
  Entry(
    'A',
    <Entry>[
      Entry(
        'A11',
        <Entry>[
          Entry('A21'),
          Entry('A22'),
        ],
      ),
      Entry('A12'),
    ],
  ),
  Entry(
    'B',
    <Entry>[
      Entry(
        'B11',
        <Entry>[
          Entry('B21'),
        ],
      ),
    ],
  ),
  Entry(
    'C',
  ),
];

// Displays one Entry. If the entry has children then it's displayed
// with an ExpansionTile.
class EntryItem extends StatelessWidget {
  const EntryItem(this.entry);

  final Entry entry;

  Widget _buildTiles(Entry root) {
    if (root.children.isEmpty) {
      return Padding(
        padding: const EdgeInsets.only(left: 10.0),
        child: ListTile(title: Text(root.title)),
      );
    }
    return Padding(
      padding: const EdgeInsets.only(left: 10.0),
      child: ExpansionTile(
        key: PageStorageKey<Entry>(root),
        title: Text(root.title),
        children: root.children.map(_buildTiles).toList(),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return _buildTiles(entry);
  }
}