File I/O

Save and load data with dart:io.

File input/output

To save tasks to a file you use the File class from dart:io. import 'dart:io'; is required.

You write with File('tasks.txt').writeAsStringSync(content) and read with .readAsStringSync(). This makes data persistent.

Synchronous methods suit simple command-line programs; asynchronous alternatives are preferred for large files.

A File example

Typical usage: var file = File('tasks.txt'); file.writeAsStringSync('data'); print(file.readAsStringSync());.

Here you first write to the file, then read the same file and print it. writeAsStringSync creates the file (or overwrites it).

To write many values you join them line by line with tasks.map((t) => t.title).join('\n').

Exercise Write tasks to a file and read back

Add import 'dart:io';. In main define var tasks = <Task>[Task('Code write'), Task('Test write')];. Create var file = File('tasks.txt');. Write the titles with file.writeAsStringSync(tasks.map((t) => t.title).join('\n'));. Print with print(file.readAsStringSync());.

Show example solution

import 'dart:io';

abstract class Trackable {
  bool get isDone;
}

class Task implements Trackable {
  final String title;
  bool done;
  Task(this.title, {this.done = false});

  @override
  bool get isDone => done;
}

void main() {
  var tasks = <Task>[Task('Code write'), Task('Test write')];
  var file = File('tasks.txt');
  file.writeAsStringSync(tasks.map((t) => t.title).join('\n'));
  print(file.readAsStringSync());
}

Test yourself

Which method writes to a file?
- print
- writeAsStringSync
- save
- toString
Show answer

writeAsStringSync — writeAsStringSync writes a string to a File.
dart:io import
```
import 'dart:____';
```
Show answer
```
import 'dart:io';
```
File input/output parts

import 'dart:io'

Import
File(...)

File object
writeAsStringSync

Writing
readAsStringSync

Reading

Next lesson: Putting it together

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