Styjun

I get the list of files from the user's folder. The names of the files I transfer to the ListView.builder. It's work, but I think, this is bad architecture.

A method _getFilesFromDir() call with a high frequency.

How to make the correct list generation, so as not to update the interface without changing the file list?

class CharacteristList extends StatefulWidget 
 @override
 _CharacteristListState createState() => new _CharacteristListState();
 
class _CharacteristListState extends State<CharacteristList> 
 List<String> filesList = new List<String>();
 List<String> filesL = new List<String>();
 @override 
 void initState() 
 super.initState();
 filesList = [];
 
 Future<List<String>> _getFilesFromDir() async
 filesL = await FilesInDirectory().getFilesFromDir();
 setState(() 
 filesList = filesL;
 );
 return filesList;
 
 _getFilesCount()
 _getFilesFromDir();
 int count = filesList.length;
 return count;
 
 @override
 Widget build(BuildContext context) 
 return new Scaffold(
 appBar: new AppBar(
 title: const Text('Список документов'),
 ),
 body: new Column(
 children: <Widget>[
 new Expanded(
 child: new ListView.builder(
 //TODO не успевает сформировать список файлов
 itemCount: _getFilesCount(),
 itemBuilder: (context, index)
 return new CharacteristListItem(filesList[index]);
 ,
 ),
 ),
 ],
 ),
 floatingActionButton: new FloatingActionButton(
 onPressed: () 
 Navigator.push(context,
 new MaterialPageRoute(builder: (context)
 => new StartScreen()),
 );,
 child: new Icon(Icons.add),
 ),
 );
 

Don't call _getFilesCount() in build(). build() can be called very frequently. Call it in initState() and store the result instead of re-reading over and over again.

I changed the architecture of the class - I used FutureBuilder.

class _CharacteristListState extends State<CharacteristList> 

 @override
 Widget build(BuildContext context) 

 return new Scaffold(
 appBar: new AppBar(
 title: const Text('Список документов'),
 ),
 body: new Center(
 child: new Column(
 children: <Widget>[
 new FutureBuilder(
 future: _inFutureList(),
 builder: (BuildContext context, AsyncSnapshot snapshot) 
 if(snapshot.connectionState == ConnectionState.waiting)
 return new Text('Data is loading...');
 
 else
 return customBuild(context, snapshot);
 
 
 )
 ],
 ),
 ),
 floatingActionButton: new FloatingActionButton(
 onPressed: () 
 Navigator.push(context,
 new MaterialPageRoute(builder: (context)
 => new StartScreen()),
 );,
 child: new Icon(Icons.add),
 ),
 );
 

 Widget customBuild(BuildContext context, AsyncSnapshot snapshot)
 List<String> values = snapshot.data;
 return new Container(
 child: new Expanded(
 child: new ListView.builder(
 itemCount: values.length,
 itemBuilder: (context, index)
 return new CharacteristListItem(values[index]);
 ,
 ),
 )
 );
 

 Future<List<String>>_inFutureList() async
 var filesList = new List<String>();
 filesList = await FilesInDirectory().getFilesFromDir();
 await new Future.delayed(new Duration(milliseconds: 500));
 return filesList;
 

 // add dependancy in pubspec.yaml
 path_provider:

 import 'dart:io' as io;
 import 'package:path_provider/path_provider.dart';

 //Declare Globaly
 String directory;
 List file = new List();
 @override
 void initState() 
 // TODO: implement initState
 super.initState();
 _listofFiles();
 

 // Make New Function
 void _listofFiles() async 
 directory = (await getApplicationDocumentsDirectory()).path;
 setState(() 
 file = io.Directory("$directory/resume/").listSync(); //use your folder name insted of resume.
 );
 

 // Build Part
 @override
 Widget build(BuildContext context) 
 return MaterialApp(
 navigatorKey: navigatorKey,
 title: 'List of Files',
 home: Scaffold(
 appBar: AppBar(
 title: Text("Get List of Files with whole Path"),
 ),
 body: Container(
 child: Column(
 children: <Widget>[
 // your Content if there
 Expanded(
 child: ListView.builder(
 itemCount: file.length,
 itemBuilder: (BuildContext context, int index) 
 return Text(file[index].toString());
 ),
 )
 ],
 ),
 ),
 ),
 );