Dart Cheat Sheet

userObject?.userName //The code snippet above is equivalent to following: (userObject != null) ? userObject.userName : null //You can chain multiple uses of ?. together in a single expression userObject?.userName?.toString() // The preceeding code returns null and never calls toString() if either userObject or userObject.userName is null 

// allows you to make a sequence of operations on the same object // rather than doing this var user = User(); user.name = "Nicola"; user.email = "[[email protected]](/cdn-cgi/l/email-protection)"; user.age = 24; // you can do this var user = User() ..name = "Nicola" ..email = "[[email protected]](/cdn-cgi/l/email-protection)" ..age = 24; 

// to insert multiple values into a collection. var list = [1, 2, 3]; var list2 = [0, ...list]; print(list2.length); //Print: 4 

// condition ? exprIfTrue : exprIfFalse bool isAvailable; isAvailable ? orderproduct() : addToFavourite(); 

int x; // The initial value of any object is null // ?? null aware operator x ??=6; // ??= assignment operator, which assigns a value of a variable only if that variable is currently null print(x); //Print: 6 x ??=3; print(x); // Print: 6 - result is still 6 print(null ?? 10); // Prints: 10. Display the value on the left if it's not null else return the value on the right 

// functionswhich are asynchronous: they return after setting up a possibly time-consuming operation // The async and await keywords support asynchronous programming Future<String> login() { String userName="Temidjoy"; return Future.delayed( Duration(seconds: 4), () => userName); } // Asynchronous main() async { print('Authenticating please wait...'); print(await userName()); } 

// To ensure that some code runs whether or not an exception is thrown try { cookFood(); } catch (e) { print('Error: $e'); // Handle the exception first. } finally { cleanKitchen(); // Then clean up. } 

try { int c = 3/0; print(c); } on IntegerDivisionByZeroException { // A specific exception print('Can not divide integer by 0.') } on Exception catch (e) { // Anything else that is an exception print('Unknown exception: $e'); } catch (e) { // No specified type, handles all print('Something really unknown: $e'); } 

// throws or raises and exception throw IntegerDivisionByZeroException(); // You can also throw arbitrary objects throw "Product out of stock!"; 

class Phone { void use(){ _call(); _sendMessage(); } } // Use extends to create a subclass class SmartPhone extends Phone { void use(){ // use super to refer to the superclass super.use(); _takePhotos(); _playGames(); } } 

// A person. The implicit interface contains greet(). class Person { // In the interface, but visible only in this library. final String _name; // Not in the interface, since this is a constructor. Person(this._name); // In the interface. String greet(String who) => 'Hello, $who. I am $\_name.'; } // An implementation of the Person interface. class Impostor implements Person { String get _name => ''; String greet(String who) => 'Hi $who. Do you know who I am?'; } String greetBob(Person person) => person.greet('Bob'); void main() { print(greetBob(Person('Kathy'))); // Hello, Bob. I am Kathy. print(greetBob(Impostor())); // Hi Bob. Do you know who I am? } 

// provide read and write access to an object’s properties class Cat { String name; // getter String get catName { return name; } // setter void set catName(String name){ this.name = name; } } 

// abstract class—a class that can’t be instantiated // This class is declared abstract and thus can't be instantiated. abstract class AbstractContainer { // Define constructors, fields, methods... void updateChildren(); // Abstract method. } 

class Cat { String name; Cat(this.name); } void main(){ Cat myCat = Cat("Kitty"); print(myCat.name); // Prints: Kitty } 

// instance of a class // below myCat is Object of class Cat void main(){ Cat myCat = Cat(); myCat.name = "Kitty"; myCat.voice(); // Prints: Meow } 

class Cat { String name; // method void voice(){ print("Meow"); } } 

// small one line functions that dont have name int add(a,b) => a+b; // lambda functions mostly passed as parameter to other functions const list = ['apples', 'bananas', 'oranges']; list.forEach( (item) => print('${list.indexOf(item)}: $item')); //Prints: 0: apples 1: bananas 2: oranges 

// functions that contain just one expression, you can use a shorthand syntax bool isFav(Product product) => favProductsList.contains(product); 

// a map is an object that associates keys and values var person = Map<String, String>(); // To initialize the map, do this: person['firstName'] = 'Nicola'; person['lastName'] = 'Tesla'; print(person); //Print: {firstName: Nicola, lastName: Tesla} print(person['lastName']); //Print: Tesla var nobleGases = { // Key: Value 2: 'helium', 10: 'neon', 18: 'argon', }; 

// A set in Dart is an unordered collection of unique items. var halogens = {'fluorine', 'chlorine', 'bromine', 'iodine', 'astatine'}; // to create an empty set var names = <String>{}; Set<String> names = {}; // This works, too. //var names = {}; // Creates a map, not a set. 

// ordered group of objects var list = [1, 2, 3]; print(list.length); //Print: 3 print(list[1]); //Print: 2 // other ways of list declaration and initializations List<String> cities = <String>["New York", "Mumbai", "Tokyo"]; // To create a list that’s a compile-time constant const constantCities = const ["New York", "Mumbai", "Tokyo"]; 

for(int i=0; i< 10; i++){ print(i); } var numbers = [1,2,3]; // for-in loop for lists for(var number in numbers){ print(number); } 

do { workHard(); } while (!dreamsAchieved); 

do-while loop verifies the condition after the execution of the statements inside the loop

while (!dreamsAchieved) { workHard(); } 

while loop check condition before iteration of the loop

enum Pet {dog, cat} Pet myPet = Pet.dog; switch(myPet){ case Pet.dog: print('My Pet is Dog.'); break; case Pet.cat: print('My Pet is Cat.'); break; default: print('I don\'t have a Pet'); } // Prints: My Pet is Dog. 

if(age < 18){ print("Teen"); } else if( age > 18 && age <60){ print("Adult"); } else { print("Old"); } 

// !expr inverts the expression (changes false to true, and vice versa) // || logical OR // && logical AND bool isOutOfStock = false; int quantity = 3; if (!isOutOfStock && (quantity == 2 || quantity == 3)) { // ...Order the product... } 

print(2 == 2); //Print: true - Equal print(2 != 3); //Print: true - Not Equal print(3 > 2); //Print: true - Grater than print(2 < 3); //Print: true - Less than print(3 >= 3); //Print: true - Greater than or equal to print(2 <= 3); //Print: true - Less than or equal to 

print(2 + 3); //Print: 5 print(2 - 3); //Print: -1 print(2 * 3); //Print: 6 print(5 / 2); //Print: 2.5 - Result is a double print(5 ~/ 2); //Print: 2 - Result is an int print(5 % 2); //Print: 1 - Remainder int a = 1, b; // Increment b = ++a; // preIncrement - Increment a before b gets its value. b = a++; // postIncrement - Increment a AFTER b gets its value. //Decrement b = --a; // predecrement - Decrement a before b gets its value. b = a--; // postdecrement - Decrement a AFTER b gets its value. 

// Importing core libraries import 'dart:math'; // Importing libraries from external packages import 'package:test/test.dart'; // Importing files import 'path/to/my\_other\_file.dart'; 

// This is a normal, one-line comment. /// This is a documentation comment, used to document libraries, /// classes, and their members. Tools like IDEs and dartdoc treat /// doc comments specially. /\* Comments like these are also supported. \*/ 

// can use single or double qoutes for String type var firstName = 'Nicola'; var lastName = "Tesla"; //can embed variables in string with $ String fullName = "$firstName $lastName"; // concatenate with + var name = "Albert " + "Einstein"; String upperCase = '${firstName.toUpperCase()}'; print(upperCase); //Print: NICOLA 

int age = 20; // integers, range -2^63 to 2^63 - 1 double height = 1.85; // floating-point numbers // You can also declare a variable as a num num x = 1; // x can have both int and double values num += 2.5; print(num); //Print: 3.5 String name = "Nicola"; bool isFavourite = true; bool isLoaded = false; 

int x = 2; // explicitly typed var p = 5; // type inferred - Generic var with type inference dynamic z = 8; // variable can take on any type z = "cool"; // cool // if you never intend to change a variable use final or const. Something like this: final email = "[[email protected]](/cdn-cgi/l/email-protection)"; // Same as var but cannot be reassigned final String email = "[[email protected]](/cdn-cgi/l/email-protection)"; // you can't change the value const qty = 5; // Compile-time constant 

// top-level function where app execution starts void main(){ print("Hello World!"); // Print to console } 

Every app has a main() function