Dart/dart.pdf.txt

dart

#dart

Table of Contents

About

Chapter 1: Getting started with dart

Remarks

Links

Documentation

FAQ

Versions

Examples

Installation or Setup

Automated installation and updates

Manual install

Hello, World!

Http Request

Html

Dart

Example

Getters and Setters

Chapter 2: Asynchronous Programming

Examples

Returning a Future using a Completer

Async and Await

Converting callbacks to Futures

Chapter 3: Classes

Examples

Creating a class

Members

Constructors

Chapter 4: Collections

Examples

Creating a new List

1

2

2

2

2

3

3

5

5

5

5

5

6

6

6

6

6

8

8

8

8

9

10

10

10

10

11

13

13

13

Creating a new Set

Creating a new Map

Map each element in the collection.

Filter a list

Chapter 5: Comments

Syntax

Remarks

Examples

End of Line Comment

Multi-Line Comment

Documentation using Dartdoc

Chapter 6: Control Flow

Examples

If Else

While Loop

For Loop

Switch Case

Chapter 7: Converting Data

Examples

JSON

Chapter 8: Dart-JavaScript interoperability

Introduction

Examples

Calling a global function

Wrapping JavaScript classes/namespaces

Passing object literals

Chapter 9: Date and time

Examples

Basic usage of DateTime

Chapter 10: Enums

Examples

Basic usage

13

13

14

14

16

16

16

16

16

16

16

18

18

18

18

19

19

21

21

21

22

22

22

22

22

23

24

24

24

25

25

25

Chapter 11: Exceptions

Remarks

Examples

Custom exception

Chapter 12: Functions

Remarks

Examples

Functions with named parameters

Function scoping

Chapter 13: Libraries

Remarks

Examples

Using libraries

Libraries and visibility

Specifying a library prefix

Importing only part of a library

Lazily loading a library

Chapter 14: List Filters

Introduction

Examples

Filtering a list of integers

Chapter 15: Pub

Remarks

Examples

pub build

pub serve

Chapter 16: Regular Expressions

Syntax

Parameters

Remarks

Examples

26

26

26

26

27

27

27

27

27

29

29

29

29

29

30

30

30

32

32

32

32

33

33

33

33

33

34

34

34

34

34

Create and use a Regular Expression

Chapter 17: Strings

Examples

Concatenation and interpolation

Valid strings

Building from parts

Credits

34

35

35

35

35

35

37

About

You can share this PDF with anyone you feel could benefit from it, downloaded the latest version 
from: dart

It is an unofficial and free dart ebook created for educational purposes. All the content is extracted 
from Stack Overflow Documentation, which is written by many hardworking individuals at Stack 
Overflow. It is neither affiliated with Stack Overflow nor official dart.

The content is released under Creative Commons BY-SA, and the list of contributors to each 
chapter are provided in the credits section at the end of this book. Images may be copyright of 
their respective owners unless otherwise specified. All trademarks and registered trademarks are 
the property of their respective company owners.

Use the content presented in this book at your own risk; it is not guaranteed to be correct nor 
accurate, please send your feedback and corrections to [email protected]

https://riptutorial.com/

1

Chapter 1: Getting started with dart

Remarks

Dart is an open-source, class-based, optionally-typed programming language for building web 
applications--on both the client and server--created by Google. Dart’s design goals are:

•
•
•

Create a structured yet flexible language for web programming.
Make Dart feel familiar and natural to programmers and thus easy to learn.
Ensure that Dart delivers high performance on all modern web browsers and environments 
ranging from small handheld devices to server-side execution.

Dart targets a wide range of development scenarios, from a one-person project without much 
structure to a large-scale project needing formal types in the code to state programmer intent.

To support this wide range of projects, Dart provides the following features and tools:

•

•
•
•
•

Optional types: this means you can start coding without types and add them later as 
needed.
Isolates: concurrent programming on server and client
Easy DOM access: using CSS selectors (the same way that jQuery does it)
Dart IDE Tools: Dart plugins exist for many commonly used IDEs, Ex: WebStorm.
Dartium: a build of the Chromium Web Browser with a built-in Dart Virtual Machine

Links

•
•
•
•
•
•
•

The Dart Homepage
Official Dart News & Updates
The Dartosphere - A collection of recent Dart blog posts
Dartisans Dartisans community on Google+
Dart Web Development - Google Groups Page
Dart Language Misc - Google Groups Page
DartLang sub-Reddit

Documentation

•
•
•
•

Tour of the Dart Language
Tour of the Dart Libraries
Dart Code samples
Dart API Reference

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2

FAQ

•

Frequently Asked Questions

Versions

Version

Release Date

1.22.1

1.22.0

1.21.1

1.21.0

1.20.1

1.20.0

1.19.1

1.19.0

1.18.1

1.18.0

1.17.1

1.17.0

1.16.1

1.16.0

1.15.0

1.14.2

1.14.1

1.14.0

1.13.2

1.13.1

1.13.0

2017-02-22

2017-02-14

2016-01-13

2016-12-07

2016-10-13

2016-10-11

2016-09-07

2016-08-26

2016-08-02

2016-07-27

2016-06-10

2016-06-06

2016-05-23

2016-04-26

2016-03-09

2016-02-09

2016-02-03

2016-01-28

2016-01-05

2015-12-17

2015-11-18

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3

Version

Release Date

1.12.2

1.12.1

1.12.0

1.11.3

1.11.1

1.11.0

1.10.1

1.10.0

1.9.3

1.9.1

1.8.5

1.8.3

1.8.0

1.7.2

1.6.0

1.5.8

1.5.3

1.5.2

1.5.1

1.4.3

1.4.2

1.4.0

1.3.6

1.3.3

1.3.0

2015-10-21

2015-09-08

2015-08-31

2015-08-03

2015-07-02

2015-06-24

2015-05-11

2015-04-24

2015-04-13

2015-03-25

2015-01-13

2014-12-01

2014-11-27

2014-10-14

2014-08-27

2014-07-29

2014-07-03

2014-07-02

2014-06-24

2014-06-16

2014-05-27

2014-05-20

2014-04-30

2014-04-16

2014-04-08

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Version

Release Date

1.2.0

1.1.3

1.1.1

2014-02-25

2014-02-06

2014-01-15

1.0.0.10_r30798

2013-12-02

1.0.0.3_r30188

2013-11-12

0.8.10.10_r30107 2013-11-08

0.8.10.6_r30036

2013-11-07

0.8.10.3_r29803

2013-11-04

Examples

Installation or Setup

The Dart SDK includes everything you need to write and run Dart code: VM, libraries, analyzer, 
package manager, doc generator, formatter, debugger, and more. If you are doing web 
development, you will also need Dartium.

Automated installation and updates

•
•
•

Installing Dart on Windows
Installing Dart on Mac
Installing Dart on Linux

Manual install

You can also manually install any version of the SDK.

Hello, World!

Create a new file named hello_world.dart with the following content:

void main() { 
  print('Hello, World!'); 
}

In the terminal, navigate to the directory containing the file hello_world.dart and type the following:

dart hello_world.dart

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Hit enter to display Hello, World! in the terminal window.

Http Request

Html

<img id="cats"></img>

Dart

import 'dart:html'; 

/// Stores the image in [blob] in the [ImageElement] of the given [selector]. 
void setImage(selector, blob) { 
  FileReader reader = new FileReader(); 
  reader.onLoad.listen((fe) { 
    ImageElement image = document.querySelector(selector); 
    image.src = reader.result; 
  }); 
  reader.readAsDataUrl(blob); 
} 

main() async { 
  var url = "https://upload.wikimedia.org/wikipedia/commons/2/28/Tortoiseshell_she-cat.JPG"; 

  // Initiates a request and asynchronously waits for the result. 
  var request = await HttpRequest.request(url, responseType: 'blob'); 
  var blob = request.response; 
  setImage("#cats", blob); 
}

Example

see Example on https://dartpad.dartlang.org/a0e092983f63a40b0b716989cac6969a

Getters and Setters

void main() { 
  var cat = new Cat(); 

  print("Is cat hungry? ${cat.isHungry}");  // Is cat hungry? true 
  print("Is cat cuddly? ${cat.isCuddly}");  // Is cat cuddly? false 
  print("Feed cat."); 
  cat.isHungry = false; 
  print("Is cat hungry? ${cat.isHungry}");  // Is cat hungry? false 
  print("Is cat cuddly? ${cat.isCuddly}");  // Is cat cuddly? true 
} 

class Cat { 
  bool _isHungry = true; 

  bool get isCuddly => !_isHungry; 

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  bool get isHungry => _isHungry; 
  bool set isHungry(bool hungry) => this._isHungry = hungry; 
}

Dart class getters and setters allow APIs to encapsulate object state changes.

See dartpad example here: https://dartpad.dartlang.org/c25af60ca18a192b84af6990f3313233

Read Getting started with dart online: https://riptutorial.com/dart/topic/843/getting-started-with-dart

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Chapter 2: Asynchronous Programming

Examples

Returning a Future using a Completer

Future<Results> costlyQuery() { 
  var completer = new Completer(); 

  database.query("SELECT * FROM giant_table", (results) { 
    // when complete 
    completer.complete(results); 
  }, (error) { 
    completer.completeException(error); 
  }); 

  // this returns essentially immediately, 
  // before query is finished 
  return completer.future; 
}

Async and Await

import 'dart:async'; 

Future main() async { 
  var value = await _waitForValue(); 
  print("Here is the value: $value"); 
  //since _waitForValue() returns immediately if you un it without await you won't get the 
result 
  var errorValue = "not finished yet"; 
  _waitForValue(); 
  print("Here is the error value: $value");// not finished yet 
} 

Future<int> _waitForValue() => new Future((){ 

  var n = 100000000; 

  // Do some long process 
  for (var i = 1; i <= n; i++) { 
    // Print out progress: 
    if ([n / 2, n / 4, n / 10, n / 20].contains(i)) { 
      print("Not done yet..."); 
    } 

    // Return value when done. 
    if (i == n) { 
      print("Done."); 
      return i; 
    } 
  } 
});

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See example on Dartpad: https://dartpad.dartlang.org/11d189b51e0f2680793ab3e16e53613c

Converting callbacks to Futures

Dart has a robust async library, with Future, Stream, and more. However, sometimes you might 
run into an asynchronous API that uses callbacks instead of Futures. To bridge the gap between 
callbacks and Futures, Dart offers the Completer class. You can use a Completer to convert a 
callback into a Future.

Completers are great for bridging a callback-based API with a Future-based API. For example, 
suppose your database driver doesn't use Futures, but you need to return a Future. Try this code:

  // A good use of a Completer. 

  Future doStuff() { 
    Completer completer = new Completer(); 
    runDatabaseQuery(sql, (results) { 
      completer.complete(results); 
    }); 
    return completer.future; 
  }

If you are using an API that already returns a Future, you do not need to use a Completer.

Read Asynchronous Programming online: https://riptutorial.com/dart/topic/2520/asynchronous-
programming

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Chapter 3: Classes

Examples

Creating a class

Classes can be created as follow:

class InputField { 
  int maxLength; 
  String name; 
}

The class can be instantiated using the new keyword after which the field values will be null by 
default.

var field = new InputField();

Field values can then be accessed:

// this will trigger the setter 
field.name = "fieldname"; 

// this will trigger the getter 
print(field.name);

Members

A class can have members.

Instance variables can be declared with/without type annotations, and optionally initialized. 
Uninitialised members have the value of null, unless set to another value by the constructor.

class Foo { 
  var member1; 
  int member2; 
  String member3 = "Hello world!"; 
}

Class variables are declared using the static keyword.

class Bar { 
  static var member4; 
  static String member5; 
  static int member6 = 42; 
}

If a method takes no arguments, is fast, returns a value, and doesn't have visible side-effects, then 

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10

 
a getter method can be used:

class Foo { 
  String get bar { 
    var result; 
    // ... 
    return result; 
  } 
}

Getters never take arguments, so the parentheses for the (empty) parameter list are omitted both 
for declaring getters, as above, and for calling them, like so:

main() { 
  var foo = new Foo(); 
  print(foo.bar); // prints "bar" 
}

There are also setter methods, which must take exactly one argument:

class Foo { 
  String _bar; 

  String get bar => _bar; 

  void set bar(String value) { 
    _bar = value; 
  } 
}

The syntax for calling a setter is the same as variable assignment:

main() { 
  var foo = new Foo(); 
  foo.bar = "this is calling a setter method"; 
}

Constructors

A class constructor must have the same name as its class.

Let's create a constructor for a class Person:

class Person { 
  String name; 
  String gender; 
  int age; 

  Person(this.name, this.gender, this.age); 
}

The example above is a simpler, better way of defining the constructor than the following way, 
which is also possible:

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class Person { 
  String name; 
  String gender; 
  int age; 

  Person(String name, String gender, int age) { 
    this.name = name; 
    this.gender = gender; 
    this.age = age; 
  } 
}

Now you can create an instance of Person like this:

var alice = new Person('Alice', 'female', 21);

Read Classes online: https://riptutorial.com/dart/topic/1511/classes

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Chapter 4: Collections

Examples

Creating a new List

Lists can be created in multiple ways.

The recommended way is to use a List literal:

var vegetables = ['broccoli', 'cabbage'];

The List constructor can be used as well:

var fruits = new List();

If you prefer stronger typing, you can also supply a type parameter in one of the following ways:

var fruits = <String>['apples', 'oranges']; 
var fruits = new List<String>();

For creating a small growable list, either empty or containing some known initial values, the literal 
form is preferred. There are specialized constructors for other kinds of lists:

var fixedLengthList1 = new List(8); 
var fixedLengthList2 = new List.filled(8, "initial text"); 
var computedValues = new List.generate(8, (n) => "x" * n); 
var fromIterable = new List<String>.from(computedValues.getRange(2, 5));

See also the Effective Dart style guide about collections.

Creating a new Set

Sets can be created via the constructor:

var ingredients = new Set(); 
ingredients.addAll(['gold', 'titanium', 'xenon']);

Creating a new Map

Maps can be created in multiple ways.

Using the constructor, you can create a new map as follow:

var searchTerms = new Map();

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13

Types for the key and value can also be defined using generics:

var nobleGases = new Map<int, String>(); 
var nobleGases = <int, String>{};

Maps can otherwise be created using the map literal:

var map = { 
    "key1": "value1", 
    "key2": "value2" 
};

Map each element in the collection.

All collection objects contain a map method that takes a Function as an argument, which must take 
a single argument. This returns an Iterable backed by the collection. When the Iterable is 
iterated, each step calls the function with a new element of the collection, and the result of the call 
becomes the next element of the iteration.

You can turn an Iterable into a collection again by using the Iterable.toSet() or Iterable.toList() 
methods, or by using a collection constructor which takes an iterable like Queue.from or List.from.

Example:

main() { 
  var cats = [ 
    'Abyssinian', 
    'Scottish Fold', 
    'Domestic Shorthair' 
  ]; 

  print(cats); // [Abyssinian, Scottish Fold, Domestic Shorthair] 

  var catsInReverse = 
  cats.map((String cat) { 
    return new String.fromCharCodes(cat.codeUnits.reversed); 
  }) 
  .toList(); // [nainissybA, dloF hsittocS, riahtrohS citsemoD] 

  print(catsInReverse); 
}

See dartpad example here: https://dartpad.dartlang.org/a18367ff767f172b34ff03c7008a6fa1

Filter a list

Dart allows to easily filter a list using where.

var fruits = ['apples', 'oranges', 'bananas']; 
fruits.where((f) => f.startsWith('a')).toList(); //apples

Of course you can use some AND or OR operators in your where clause.

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Read Collections online: https://riptutorial.com/dart/topic/859/collections

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Chapter 5: Comments

Syntax

•
•
•

// Single-line comment
/* Multi-line/In-line comment */
/// Dartdoc comment

Remarks

It is good practice to add comments to your code to explain why something is done or to explain 
what something does. This helps any future readers of your code to more easily understand your 
code.

Related topic(s) not on StackOverflow:

•

Effective Dart: Documentation

Examples

End of Line Comment

Everything to the right of // in the same line is commented.

int i = 0; // Commented out text

Multi-Line Comment

Everything between /* and */ is commented.

void main() { 
  for (int i = 0; i < 5; i++) { 
    /* This is commented, and 
    will not affect code */ 
    print('hello ${i + 1}'); 
  } 
}

Documentation using Dartdoc

Using a doc comment instead of a regular comment enables dartdoc to find it and generate 
documentation for it.

/// The number of characters in this chunk when unsplit. 
int get length => ...

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You are allowed to use most markdown formatting in your doc comments and dartdoc will process 
it accordingly using the markdown package.

/// This is a paragraph of regular text. 
/// 
/// This sentence has *two* _emphasized_ words (i.e. italics) and **two** 
/// __strong__ ones (bold). 
/// 
/// A blank line creates another separate paragraph. It has some `inline code` 
/// delimited using backticks. 
/// 
/// * Unordered lists. 
/// * Look like ASCII bullet lists. 
/// * You can also use `-` or `+`. 
/// 
/// Links can be: 
/// 
/// * http://www.just-a-bare-url.com 
/// * [with the URL inline](http://google.com) 
/// * [or separated out][ref link] 
/// 
/// [ref link]: http://google.com 
/// 
/// # A Header 
/// 
/// ## A subheader

Read Comments online: https://riptutorial.com/dart/topic/2436/comments

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Chapter 6: Control Flow

Examples

If Else

Dart has If Else:

if (year >= 2001) { 
  print('21st century'); 
} else if (year >= 1901) { 
  print('20th century'); 
} else { 
  print('We Must Go Back!'); 
}

Dart also has a ternary if operator:

var foo = true; 
print(foo ? 'Foo' : 'Bar'); // Displays "Foo".

While Loop

While loops and do while loops are allowed in Dart:

while(peopleAreClapping()) { 
  playSongs(); 
}

and:

do { 
  processRequest(); 
} while(stillRunning());

Loops can be terminated using a break:

while (true) { 
  if (shutDownRequested()) break; 
  processIncomingRequests(); 
}

You can skip iterations in a loop using continue:

for (var i = 0; i < bigNumber; i++) { 
  if (i.isEven){ 
    continue; 
  } 
  doSomething(); 

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}

For Loop

Two types of for loops are allowed:

for (int month = 1; month <= 12; month++) { 
  print(month); 
}

and:

for (var object in flybyObjects) { 
  print(object); 
}

The for-in loop is convenient when simply iterating over an Iterable collection. There is also a 
forEach method that you can call on Iterable objects that behaves like for-in:

flybyObjects.forEach((object) => print(object));

or, more concisely:

flybyObjects.forEach(print);

Switch Case

Dart has a switch case which can be used instead of long if-else statements:

var command = 'OPEN'; 

switch (command) { 
  case 'CLOSED': 
    executeClosed(); 
    break; 
  case 'OPEN': 
    executeOpen(); 
    break; 
  case 'APPROVED': 
    executeApproved(); 
    break; 
  case 'UNSURE': 
    // missing break statement means this case will fall through 
    // to the next statement, in this case the default case 
  default: 
    executeUnknown(); 
}

You can only compare integer, string, or compile-time constants. The compared objects must be 
instances of the same class (and not of any of its subtypes), and the class must not override ==.

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One surprising aspect of switch in Dart is that non-empty case clauses must end with break, or 
less commonly, continue, throw, or return. That is, non-empty case clauses cannot fall through. 
You must explicitly end a non-empty case clause, usually with a break. You will get a static 
warning if you omit break, continue, throw, or return, and the code will error at that location at 
runtime.

var command = 'OPEN'; 
switch (command) { 
  case 'OPEN': 
    executeOpen(); 
    // ERROR: Missing break causes an exception to be thrown!! 

  case 'CLOSED': // Empty case falls through 
  case 'LOCKED': 
    executeClosed(); 
    break; 
}

If you want fall-through in a non-empty case, you can use continue and a label:

      var command = 'OPEN'; 
      switch (command) { 
        case 'OPEN': 
          executeOpen(); 
          continue locked; 
locked: case 'LOCKED': 
          executeClosed(); 
          break; 
      }

Read Control Flow online: https://riptutorial.com/dart/topic/923/control-flow

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Chapter 7: Converting Data

Examples

JSON

    import 'dart:convert'; 

    void main() { 
        var jsonString = """ 
          { 
            "cats": { 
                    "abysinnian": { 
                        "origin": "Burma", 
                        "behavior": "playful" 
                    } 
                } 
        } 
      """; 

      var obj = JSON.decode(jsonString); 

      print(obj['cats']['abysinnian']['behavior']); // playful 
    }

See example on dartpad: https://dartpad.dartlang.org/7d5958cf10e611b36326f27b062108fe

Read Converting Data online: https://riptutorial.com/dart/topic/2778/converting-data

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Chapter 8: Dart-JavaScript interoperability

Introduction

Dart-JavaScript interoperability lets us run JavaScript code from our Dart programs.

The interoperability is achieved by using the js library to create Dart stubs. These stubs describe 
the interface we'd like to have with the underlying JavaScript code. At runtime calling the Dart stub 
will invoke the JavaScript code.

Examples

Calling a global function

Suppose we'd like to invoke the JavaScript function JSON.stringify which receives an object, 
encodes it into a JSON string and returns it.

All we'd have to do is write the function signature, mark it as external and annotate it with the @JS 
annotation:

 @JS("JSON.stringify") 
external String stringify(obj);

The @JS annotation will be used from here on out to mark Dart classes that we'd like to use in 
JavaScript as well.

Wrapping JavaScript classes/namespaces

Suppose we'd like to wrap the Google Maps JavaScript API google.maps:

@JS('google.maps') 
library maps; 

import "package:js/js.dart"; 

@JS() 
class Map { 
  external Map(Location location); 
  external Location getLocation(); 
}

We now have the Map Dart class which corresponds to the JavaScript google.maps.Map class.

Running new Map(someLocation) in Dart will invoke new google.maps.Map(location) in JavaScript.

Note that you don't have to name your Dart class the same as the JavaScript class:

@JS("LatLng") 

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class Location { 
  external Location(num lat, num lng); 
}

The Location Dart class corresponds to the google.maps.LatLng class.

Using inconsistent names is discouraged as they can create confusion.

Passing object literals

It's common practice in JavaScript to pass object literals to functions:

// JavaScript 
printOptions({responsive: true}); 
Unfortunately we cannot pass Dart Map objects to JavaScript in these cases.

What we have to do is create a Dart object that represents the object literal and contains all of its 
fields:

// Dart 
@JS() 
@anonymous 
class Options { 
  external bool get responsive; 

  external factory Options({bool responsive}); 
}

Note that the Options Dart class doesn't correspond to any JavaScript class. As such we must 
mark it with the @anonymous annotation.

Now we can create a stub for the original printOptions function and call it with a new Options 
object:

// Dart 
@JS() 
external printOptions(Options options); 

printOptions(new Options(responsive: true));

Read Dart-JavaScript interoperability online: https://riptutorial.com/dart/topic/9240/dart-javascript-
interoperability

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Chapter 9: Date and time

Examples

Basic usage of DateTime

DateTime now = new DateTime.now(); 
DateTime berlinWallFell = new DateTime(1989, 11, 9); 
DateTime moonLanding = DateTime.parse("1969-07-20 20:18:00");  // 8:18pm

You can find more in depth information here.

Read Date and time online: https://riptutorial.com/dart/topic/3322/date-and-time

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Chapter 10: Enums

Examples

Basic usage

enum Fruit { 
  apple, banana 
} 

main() { 
  var a = Fruit.apple; 
  switch (a) { 
    case Fruit.apple: 
      print('it is an apple'); 
      break; 
  } 

  // get all the values of the enums 
  for (List<Fruit> value in Fruit.values) { 
    print(value); 
  } 

  // get the second value 
  print(Fruit.values[1]); 
}

Read Enums online: https://riptutorial.com/dart/topic/5107/enums

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Chapter 11: Exceptions

Remarks

Dart code can throw and catch exceptions. Exceptions are errors indicating that something 
unexpected happened. If the exception isn’t caught, the isolate that raised the exception is 
suspended, and typically the isolate and its program are terminated.

In contrast to Java, all of Dart’s exceptions are unchecked exceptions. Methods do not declare 
which exceptions they might throw, and you are not required to catch any exceptions.

Dart provides Exception and Error types, as well as numerous predefined subtypes. You can, of 
course, define your own exceptions. However, Dart programs can throw any non-null object—not 
just Exception and Error objects—as an exception.

Examples

Custom exception

class CustomException implements Exception { 
  String cause; 
  CustomException(this.cause); 
} 

void main() { 
  try { 
    throwException(); 
  } on CustomException { 
    print("custom exception is been obtained"); 
  } 
} 

throwException() { 
  throw new CustomException('This is my first custom exception'); 
}

Read Exceptions online: https://riptutorial.com/dart/topic/3334/exceptions

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Chapter 12: Functions

Remarks

Dart is a true object-oriented language, so even functions are objects and have a type, Function. 
This means that functions can be assigned to variables or passed as arguments to other functions. 
You can also call an instance of a Dart class as if it were a function.

Examples

Functions with named parameters

When defining a function, use {param1, param2, …} to specify named parameters:

void enableFlags({bool bold, bool hidden}) { 
  // ... 
}

When calling a function, you can specify named parameters using paramName: value

enableFlags(bold: true, hidden: false);

Function scoping

Dart functions may also be declared anonymously or nested. For example, to create a nested 
function, just open a new function block within an existing function block

void outerFunction() { 

    bool innerFunction() { 
        /// Does stuff 
    } 
}

The function innerFunction may now be used inside, and only inside, outerFunction. No other other 
functions has access to it.

Functions in Dart may also be declared anonymously, which is commonly used as function 
arguments. A common example is the sort method of List object. This method takes an optional 
argument with the following signature:

int compare(E a, E b)

The documentation states that the function must return 0 if the a and b are equal. It returns -1 if a < 
b and 1 if a > b.

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Knowing this, we can sort a list of integers using an anonymous function.

List<int> numbers = [4,1,3,5,7]; 

numbers.sort((int a, int b) { 
   if(a == b) { 
      return 0; 
   } else if (a < b) { 
      return -1; 
   } else { 
      return 1; 
   } 
});

Anonymous function may also be bound to identifiers like so:

Function intSorter = (int a, int b) { 
   if(a == b) { 
      return 0; 
   } else if (a < b) { 
      return -1; 
   } else { 
      return 1; 
   } 
}

and used as an ordinary variable.

numbers.sort(intSorter);

Read Functions online: https://riptutorial.com/dart/topic/2965/functions

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Chapter 13: Libraries

Remarks

The import and library directives can help you create a modular and shareable code base. Every 
Dart app is a library, even if it doesn’t use a library directive. Libraries can be distributed using 
packages. See Pub Package and Asset Manager for information about pub, a package manager 
included in the SDK.

Examples

Using libraries

Use import to specify how a namespace from one library is used in the scope of another library.

import 'dart:html';

The only required argument to import is a URI specifying the library. For built-in libraries, the URI 
has the special dart: scheme. For other libraries, you can use a file system path or the package: 
scheme. The package: scheme specifies libraries provided by a package manager such as the pub 
tool. For example:

import 'dart:io'; 
import 'package:mylib/mylib.dart'; 
import 'package:utils/utils.dart';

Libraries and visibility

Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts 
with an underscore _, it’s private to its library.

If you for example have class A in a separate library file (eg, other.dart), such as:

library other; 

class A { 
  int _private = 0; 

  testA() { 
    print('int value: $_private');  // 0 
    _private = 5; 
    print('int value: $_private'); // 5 
  } 
}

and then import it into your main app, such as:

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import 'other.dart'; 

void main() { 
  var b = new B(); 
  b.testB(); 
} 

class B extends A { 
  String _private; 

  testB() { 
    _private = 'Hello'; 
    print('String value: $_private'); // Hello 
    testA(); 
    print('String value: $_private'); // Hello 
  } 
}

You get the expected output:

String value: Hello 
int value: 0 
int value: 5 
String value: Hello

Specifying a library prefix

If you import two libraries that have conflicting identifiers, then you can specify a prefix for one or 
both libraries. For example, if library1 and library2 both have an Element class, then you might 
have code like this:

import 'package:lib1/lib1.dart'; 
import 'package:lib2/lib2.dart' as lib2; 
// ... 
var element1 = new Element(); // Uses Element from lib1. 
var element2 = 
    new lib2.Element();       // Uses Element from lib2.

Importing only part of a library

If you want to use only part of a library, you can selectively import the library. For example:

// Import only foo and bar. 
import 'package:lib1/lib1.dart' show foo, bar; 

// Import all names EXCEPT foo. 
import 'package:lib2/lib2.dart' hide foo;

Lazily loading a library

Deferred loading (also called lazy loading) allows an application to load a library on demand, if and 
when it’s needed. To lazily load a library, you must first import it using deferred as.

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import 'package:deferred/hello.dart' deferred as hello;

When you need the library, invoke loadLibrary() using the library’s identifier.

greet() async { 
  await hello.loadLibrary(); 
  hello.printGreeting(); 
}

In the preceding code, the await keyword pauses execution until the library is loaded. For more 
information about async and await, see more examples here asynchrony support or visit the 
asynchrony support part of the language tour.

Read Libraries online: https://riptutorial.com/dart/topic/3332/libraries

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Chapter 14: List Filters

Introduction

Dart filters lists through the List.where and List.retainWhere methods. The where function takes one 
argument: a boolean function that is applied to each element of the list. If the function evaluates to 
true then the list element is retained; if the function evaluates to false, the element is removed.

Calling theList.retainWhere(foo) is practically equivalent to setting theList = theList.where(foo).

Examples

Filtering a list of integers

[-1, 0, 2, 4, 7, 9].where((x) => x > 2) --> [4, 7, 9]

Read List Filters online: https://riptutorial.com/dart/topic/10948/list-filters

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Chapter 15: Pub

Remarks

When you install the Dart SDK, one of the tools that you get is pub. The pub tool provides 
commands for a variety of purposes. One command installs packages, another starts up an HTTP 
server for testing, another prepares your app for deployment, and another publishes your package 
to pub.dartlang.org. You can access the pub commands either through an IDE, such as 
WebStorm, or at the command line.

For an overview of these commands, see Pub Commands.

Examples

pub build

Use pub build when you’re ready to deploy your web app. When you run pub build, it generates 
the assets for the current package and all of its dependencies, putting them into new directory 
named build.

To use pub build, just run it in your package’s root directory. For example:

$ cd ~/dart/helloworld 
$ pub build 
Building helloworld...... 
Built 5 files!

pub serve

This command starts up a development server, or dev server, for your Dart web app. The dev 
server is an HTTP server on localhost that serves up your web app’s assets.

Start the dev server from the directory that contains your web app’s pubspec.yaml file:

$ cd ~/dart/helloworld 
$ pub serve 
Serving helloworld on http://localhost:8080

Read Pub online: https://riptutorial.com/dart/topic/3335/pub

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Chapter 16: Regular Expressions

Syntax

•

var regExp = RegExp(r'^(.*)$', multiLine: true, caseSensitive: false);

Parameters

Parameter

Details

String source

The regular expression as a String

{bool multiline}

Whether this is a multiline regular expression. (matches ^ and $ at the 
beginning and end of each line individually not the whole String)

{bool 
caseSensitive}

If the expression is case sensitive

Remarks

Dart regular expressions have the same syntax and semantics as JavaScript regular expressions. 
See http://ecma-international.org/ecma-262/5.1/#sec-15.10 for the specification of JavaScript 
regular expressions.

This means that any JavaScript resource you find about Regular Expressions online applies to 
dart.

Examples

Create and use a Regular Expression

var regExp = new RegExp(r"(\w+)"); 
var str = "Parse my string"; 
Iterable<Match> matches = regExp.allMatches(str);

It's a good idea to use "raw strings" (prefix with r) when writing regular expressions so you can 
use unescaped backslashes in your expression.

Read Regular Expressions online: https://riptutorial.com/dart/topic/3624/regular-expressions

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Chapter 17: Strings

Examples

Concatenation and interpolation

You can use the plus (+) operator to concatenate strings:

'Dart ' + 'is ' + 'fun!'; // 'Dart is fun!'

You can also use adjacent string literals for concatenation:

'Dart ' 'is ' 'fun!';    // 'Dart is fun!'

You can use ${} to interpolate the value of Dart expressions within strings. The curly braces can 
be omitted when evaluating identifiers:

var text = 'dartlang'; 
'$text has ${text.length} letters'; // 'dartlang has 8 letters'

Valid strings

A string can be either single or multiline. Single line strings are written using matching single or 
double quotes, and multiline strings are written using triple quotes. The following are all valid Dart 
strings:

'Single quotes'; 
"Double quotes"; 
'Double quotes in "single" quotes'; 
"Single quotes in 'double' quotes"; 

'''A 
multiline 
string'''; 

""" 
Another 
multiline 
string""";

Building from parts

Programmatically generating a String is best accomplished with a StringBuffer. A StringBuffer 
doesn't generate a new String object until toString() is called.

var sb = new StringBuffer(); 

sb.write("Use a StringBuffer"); 

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sb.writeAll(["for ", "efficient ", "string ", "creation "]); 
sb.write("if you are ") 
sb.write("building lots of strings"); 

// or you can use method cascades: 

sb 
  ..write("Use a StringBuffer") 
  ..writeAll(["for ", "efficient ", "string ", "creation "]) 
  ..write("if you are ") 
  ..write("building lots of strings"); 

var fullString = sb.toString(); 

print(fullString); 
// Use a StringBufferfor efficient string creation if you are building lots of strings 

sb.clear(); // all gone!

Read Strings online: https://riptutorial.com/dart/topic/5003/strings

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Credits

S. 
No

1

2

3

4

5

6

7

8

9

Chapters

Contributors

Getting started with 
dart

4444, Challe, Community, Damon, Florian Loitsch, Gomiero, 
Kleak, losnake, martin, Raph, Timothy C. Quinn

Asynchronous 
Programming

Challe, Damon, Ray Hulha, Zied Hamdi

Classes

Ganymede, Hoylen, Jan Vladimir Mostert, Raph

Collections

Alexi Coard, Damon, Jan Vladimir Mostert, Kleak, lrn, Pacane, 
Raph

Comments

Challe

Control Flow

Ganymede, Jan Vladimir Mostert, Pacane, Raph

Converting Data

Damon

Dart-JavaScript 
interoperability

Date and time

10 Enums

11 Exceptions

Meshulam Silk

Challe

Challe

Challe

12

Functions

Jan Vladimir Mostert, Kim Rostgaard Christensen

13

Libraries

Challe, Ganymede

14

List Filters

jxmorris12

15 Pub

Challe

16 Regular Expressions

enyo

17 Strings

Challe

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37