The fluent application creates a list of expansion panels

original text

https://medium.flutterdevs.com/expansionpanellist-in-flutter-48aa06f764e

Reference resources

• https://api.flutter.dev/flutter/material/ExpansionPanelList-class.html

Text

Learn how to Flutter The application creates a list of extension panels

In this paper , We'll talk about ExpansionPanelList In Flutter. . We will implement an extension panel list Demo , And learn how to customize its style with different attributes in your Flutter Applications .

Expansion Panel List:

It is a similar to listView Materiality of Flutter The widget . It can only have an expansion panel as a child . In some cases , We may need to display a list , The child elements can be expanded / Collapse to show / Hide some detailed data . To display such a list flutter, A file named ExapansionPanelList The widget of .

In this list , Every subelement is expsionpanel The widget . In this list , We can't use different widgets as child windows . We can use expsioncallback Property to handle the state adjustment of things ( Expand or crash ).

Demo module :

This demo video shows how to work in a Flutter Expansion panel list . It shows how the extension panel list will work in your Flutter Applications . It shows a list , In this list, children can expand / Collapse to show / Hide some details . It will show up on your device .

Constructor:

To use ExpansionPanelList, You need to call the following constructor :

const ExpansionPanelList({
  Key? key,
  this.children = const <ExpansionPanel>[],
  this.expansionCallback,
  this.animationDuration = kThemeAnimationDuration,
  this.expandedHeaderPadding = _kPanelHeaderExpandedDefaultPadding,
  this.dividerColor,
  this.elevation = 2,
})

Properties:

ExpansionPanelList Some properties of are as follows :

• > children: This property is used for expansion panels List Child elements . Their layout is similar to [ListBody].
• > expansionCallback: This property is used whenever an expansion is pressed / Callback called when the button is collapsed . The parameter passed to the callback is the index of the panel pressed , And whether the panel is currently expanded .
• > animationDuration: This property is used when expanding or collapsing , We can observe that some animations occur within a certain period of time . We can use the expansion panel List Of animationDuration Property to change the duration . We just need to provide in microseconds 、 Duration value in milliseconds or minutes .
• > expandedHeaderPadding: This property is used for padding around the panel header when expanding . By default ,16px The space is added vertically to the title during expansion ( Above and below ).
• > dividerColor: When [ expsionpanel.isexpanded ] by false when , This property defines the color of the separator . If ‘ dividerColor’ It's empty , Then use [ DividerThemeData.color ]. If null, Then use [ ThemeData.dividerColor ].
• > elevation: This property is used to define when extending [ expsionpanel ] The promotion of . This use [ kElevationToShadow ] To simulate shadows , It does not use. [ Material ] Any height characteristic of . By default , The value of elevation is 2.

How to achieve dart Code in file :

You need to implement it separately in your code :

stay lib Create a folder called main.dart The new dart file .

First , We will generate virtual data . We will create a list <Map<String, dynamic>> And add variables _ items Is equivalent to generating a list . In this list , We will add number、 id、 title、 description and isExpanded.

List<Map<String, dynamic>> _items = List.generate(
    10,
        (index) => {
      'id': index,
      'title': 'Item $index',
      'description':
      'This is the description of the item $index. Lorem Ipsum is simply dummy text of the printing and typesetting industry.',
      'isExpanded': false
    });

In the text , We will add ExpansionPanelList() The widget . In this widget , We will add an elevation of 3, Add... In parentheses expsioncallback Index and isExpanded. We will add setState () Method . In the method , We will add _ items [ index ][‘ isexpanded’] equal not isExpanded.

ExpansionPanelList(
  elevation: 3,
  expansionCallback: (index, isExpanded) {
    setState(() {
      _items[index]['isExpanded'] = !isExpanded;
    });
  },
  animationDuration: Duration(milliseconds: 600),
  children: _items
      .map(
        (item) => ExpansionPanel(
      canTapOnHeader: true,
      backgroundColor:
      item['isExpanded'] == true ? Colors._cyan_[100] : Colors._white_,
      headerBuilder: (_, isExpanded) => Container(
          padding:
          EdgeInsets.symmetric(vertical: 15, horizontal: 30),
          child: Text(
            item['title'],
            style: TextStyle(fontSize: 20),
          )),
      body: Container(
        padding: EdgeInsets.symmetric(vertical: 15, horizontal: 30),
        child: Text(item['description']),
      ),
      isExpanded: item['isExpanded'],
    ),
  )
      .toList(),
),

We will increase animationDuration by 600 millisecond . We will add child nodes , because variable_items Mapping to expsionpanel () The widget . In this widget , We will add canTapOnHeader was true,backgroundColor,headerBuilder return Container () The widget . In this widget , We're going to add padding , And add text to its sub attributes . In the text , We will add Conatiner And its sub attributes , We're going to add text . When we run the application , We should get screen output , Just like the screenshot below .

All the code

import 'package:flutter/material.dart';
import 'package:flutter_expansion_panel_list/splash_screen.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        theme: ThemeData(
          primarySwatch: Colors._teal_,
        ),
        home: Splash());
  }
}

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

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

class _HomePageState extends State<HomePage> {
  List<Map<String, dynamic>> _items = List.generate(
      10,
          (index) => {
        'id': index,
        'title': 'Item $index',
        'description':
        'This is the description of the item $index. Lorem Ipsum is simply dummy text of the printing and typesetting industry.',
        'isExpanded': false
      });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        automaticallyImplyLeading: false,
        title: Text('Flutter Expansion Panel List Demo'),
      ),
      body: SingleChildScrollView(
        child: ExpansionPanelList(
          elevation: 3,
          // Controlling the expansion behavior
          expansionCallback: (index, isExpanded) {
            setState(() {
              _items[index]['isExpanded'] = !isExpanded;
            });
          },
          animationDuration: Duration(milliseconds: 600),
          children: _items
              .map(
                (item) => ExpansionPanel(
              canTapOnHeader: true,
              backgroundColor:
              item['isExpanded'] == true ? Colors._cyan_[100] : Colors._white_,
              headerBuilder: (_, isExpanded) => Container(
                  padding:
                  EdgeInsets.symmetric(vertical: 15, horizontal: 30),
                  child: Text(
                    item['title'],
                    style: TextStyle(fontSize: 20),
                  )),
              body: Container(
                padding: EdgeInsets.symmetric(vertical: 15, horizontal: 30),
                child: Text(item['description']),
              ),
              isExpanded: item['isExpanded'],
            ),
          )
              .toList(),
        ),
      ),
    );
  }
}

Conclusion

In this paper , I have simply explained ExpansionPanelList Basic structure ; You can modify this code according to your choice . This is a small introduction extension /panellist On User Interaction From my side , Its work uses Flutter.

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