How to show in a ListView a Tree of Strings? - algorithm

Question

I have a Map<String, dynamic>, where dynamic is a dynamic tree of Strings. I need to show in a ListView (or another Widget that allow to show a Tree structure) the Strings and their children. Each String is a collapsable item (if has children) of the ListView. For example:
Text
text
text
text
text
text
text
text
text
this is the code of an example of the tree:
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);
}
this is de ouput of joinedTree:
{
A:
{
A11:
{
A21: null,
A22: null
},
A12: null
},
B:
{
B11:
{
B21: null
}
},
C: null
}

Answer 1

if your tree look like this, detail Entry class please reference full code
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',
),
];
inside ListView.builder, build item with
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(),
),
);
}
full code
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);
}
}