A reference to a file on the file system.

AFile holds apath on which operations can be performed.You can get the parent directory of the file usingparent,a property inherited fromFileSystemEntity.

Create a newFile object with a pathname to access the specified file on thefile system from your program.

var myFile = File('file.txt');

TheFile class contains methods for manipulating files and their contents.Using methods in this class, you can open and close files, read to and writefrom them, create and delete them, and check for their existence.

When reading or writing a file, you can use streams (withopenRead),random access operations (withopen),or convenience methods such asreadAsString,

Most methods in this class occur in synchronous and asynchronous pairs,for example,readAsString andreadAsStringSync.Unless you have a specific reason for using the synchronous versionof a method, prefer the asynchronous version to avoid blocking your program.

If path is a link

Ifpath is a symbolic link, rather than a file,then the methods ofFile operate on the ultimate target of thelink, except fordelete anddeleteSync, which operate onthe link.

Read from a file

The following code sample reads the entire contents from a file as a stringusing the asynchronousreadAsString method:

import 'dart:async';import 'dart:io';void main() {  File('file.txt').readAsString().then((String contents) {    print(contents);  });}

A more flexible and useful way to read a file is with aStream.Open the file withopenRead, which returns a stream thatprovides the data in the file as chunks of bytes.Read the stream to process the file contents when available.You can use various transformers in succession to manipulate thefile content into the required format, or to prepare it for output.

You might want to use a stream to read large files,to manipulate the data with transformers,or for compatibility with another API, such asWebSockets.

import 'dart:io';import 'dart:convert';import 'dart:async';void main() async {  final file = File('file.txt');  Stream<String> lines = file.openRead()    .transform(utf8.decoder)       // Decode bytes to UTF-8.    .transform(LineSplitter());    // Convert stream to individual lines.  try {    await for (var line in lines) {      print('$line: ${line.length} characters');    }    print('File is now closed.');  } catch (e) {    print('Error: $e');  }}

Write to a file

To write a string to a file, use thewriteAsString method:

import 'dart:io';void main() async {  final filename = 'file.txt';  var file = await File(filename).writeAsString('some content');  // Do something with the file.}

You can also write to a file using aStream. Open the file withopenWrite, which returns anIOSink to which you can write data.Be sure to close the sink with theIOSink.close method.

import 'dart:io';void main() async {  var file = File('file.txt');  var sink = file.openWrite();  sink.write('FILE ACCESSED ${DateTime.now()}\n');  await sink.flush();  // Close the IOSink to free system resources.  await sink.close();}

The use of asynchronous methods

To avoid unintentional blocking of the program,several methods are asynchronous and return aFuture. For example,thelength method, which gets the length of a file, returns aFuture.Wait for the future to get the result when it's ready.

import 'dart:io';void main() async {  final file = File('file.txt');  var length = await file.length();  print(length);}

In addition to length, theexists,lastModified,stat, andother methods, are asynchronous.

Special 'nul' file

On Linux and Mac '/dev/null' and on Windows '\?\NUL' refer to a special file,such that all writes to it get consumed and disappear, and all reads produce emptyoutput. Note that on Windows 'nul'(without '\?'-prefix) refers to a regular filenamed 'nul' in current directory.

Other resources

• TheFiles and directoriessection of the library tour.

• Write Command-Line Apps,a tutorial about writing command-line apps, includes information aboutfiles and directories.

Implemented types

• FileSystemEntity

Constructors

File(Stringpath)

Creates aFile object.

factory

File.fromRawPath(Uint8ListrawPath)

Creates aFile object from a raw path.

factory

File.fromUri(Uriuri)

Create aFile object from a URI.

factory

Properties

absolute→File

AFile with the absolute path ofpath.

no setteroverride

hashCode→int

The hash code for this object.

no setterinherited

isAbsolute→bool

Whether this object's path is absolute.

no setterinherited

parent→Directory

The parent directory of this entity.

no setterinherited

path→String

Get the path of the file.

no setteroverride

runtimeType→Type

A representation of the runtime type of the object.

no setterinherited

uri→Uri

AUri representing the file system entity's location.

no setterinherited

Methods

copy(StringnewPath)→Future<File>

Copies this file.

copySync(StringnewPath)→File

Synchronously copies this file.

create({boolrecursive =false,boolexclusive =false})→Future<File>

Creates the file.

createSync({boolrecursive =false,boolexclusive =false})→ void

Synchronously creates the file.

delete({boolrecursive =false})→Future<FileSystemEntity>

Deletes thisFile.

override

deleteSync({boolrecursive =false})→ void

Synchronously deletes thisFile.

override

exists()→Future<bool>

Checks whether the file system entity with this path exists.

inherited

existsSync()→bool

Synchronously checks whether the file system entity with this pathexists.

inherited

lastAccessed()→Future<DateTime>

The last-accessed time of the file.

lastAccessedSync()→DateTime

The last-accessed time of the file.

lastModified()→Future<DateTime>

Get the last-modified time of the file.

lastModifiedSync()→DateTime

Get the last-modified time of the file.

length()→Future<int>

The length of the file.

lengthSync()→int

The length of the file provided synchronously.

noSuchMethod(Invocationinvocation)→ dynamic

Invoked when a nonexistent method or property is accessed.

inherited

open({FileModemode =FileMode.read})→Future<RandomAccessFile>

Opens the file for random access operations.

openRead([int?start,int?end])→Stream<List<int>>

Creates a new independentStream for the contents of this file.

openSync({FileModemode =FileMode.read})→RandomAccessFile

Synchronously opens the file for random access operations.

openWrite({FileModemode =FileMode.write,Encodingencoding =utf8})→IOSink

Creates a new independentIOSink for the file.

readAsBytes()→Future<Uint8List>

Reads the entire file contents as a list of bytes.

readAsBytesSync()→Uint8List

Synchronously reads the entire file contents as a list of bytes.

readAsLines({Encodingencoding =utf8})→Future<List<String>>

Reads the entire file contents as lines of text using the givenEncoding.

readAsLinesSync({Encodingencoding =utf8})→List<String>

Synchronously reads the entire file contents as lines of textusing the givenEncoding.

readAsString({Encodingencoding =utf8})→Future<String>

Reads the entire file contents as a string using the givenEncoding.

readAsStringSync({Encodingencoding =utf8})→String

Synchronously reads the entire file contents as a string using thegivenEncoding.

rename(StringnewPath)→Future<File>

Renames this file.

override

renameSync(StringnewPath)→File

Synchronously renames this file.

override

resolveSymbolicLinks()→Future<String>

Resolves the path of a file system object relative to thecurrent working directory.

inherited

resolveSymbolicLinksSync()→String

Resolves the path of a file system object relative to thecurrent working directory.

inherited

setLastAccessed(DateTimetime)→Future

Modifies the time the file was last accessed.

setLastAccessedSync(DateTimetime)→ void

Synchronously modifies the time the file was last accessed.

setLastModified(DateTimetime)→Future

Modifies the time the file was last modified.

setLastModifiedSync(DateTimetime)→ void

Synchronously modifies the time the file was last modified.

stat()→Future<FileStat>

Calls the operating system'sstat() function onpath.

inherited

statSync()→FileStat

Synchronously calls the operating system'sstat() function onpath.

inherited

toString()→String

A string representation of this object.

inherited

watch({intevents =FileSystemEvent.all,boolrecursive =false})→Stream<FileSystemEvent>

Start watching theFileSystemEntity for changes.

inherited

writeAsBytes(List<int>bytes, {FileModemode =FileMode.write,boolflush =false})→Future<File>

Writes a list of bytes to a file.

writeAsBytesSync(List<int>bytes, {FileModemode =FileMode.write,boolflush =false})→ void

Synchronously writes a list of bytes to a file.

writeAsString(Stringcontents, {FileModemode =FileMode.write,Encodingencoding =utf8,boolflush =false})→Future<File>

Writes a string to a file.

writeAsStringSync(Stringcontents, {FileModemode =FileMode.write,Encodingencoding =utf8,boolflush =false})→ void

Synchronously writes a string to a file.

Operators

operator ==(Objectother)→bool

The equality operator.

inherited