Dart Cheat Sheet - Full bộ "bỏ túi" các syntax trong ngôn ngữ Dart

Dart là một ngôn ngữ mới dùng cho cả Mobile và Web với Flutter Framework, thậm chí dùng cho Backend. Để giúp mọi người dễ dàng nắm bắt ngôn ngữ này hơn, 200lab Education đã tổng hợp thành bộ "bí tịch" dưới đây để tra cứu nhanh, tăng tốc phát triển phần mềm.

1. Starting Point:

void main(){
    print('Hello world');
}

2. Variables:

int year = 2021; // explicitly typed int
var month = 01; // inferred int created with var
double day; // null

p = 'aaa'; // error when compiling

dynamic numberOfCats; // dynamic variable can have any type of value

numberOfCats = '3'; // dynamic String
numberOfCats = 0.2; // dynamic double
bool isCat = true; // boolean

3. Constants:

const hourInDay = 24; // Compile-time constants
hourInDay = 23; // error can't assign to the const variable

final age = 23; // Immutables with final
age = 24; // error can't assign to the final variable

4. Conditional Expressions:

var animal = 'fish';
if (animal == 'cat' || animal = 'bear'){
    print('That is a cute animal');
} else if (animal == 'dinosaur'){
    print('Dinosaur is extincted');
} else{
   print('That is a fly animal');
}

5. Iterations:

for (int i=0 ;i < 69; i++) {
  print(i);
} // prints 0 to 69

final list = [ 'a', 'b', 'c' , 'd', 'e'];

for(final i in list){
   print(i)
} // prints: a, b, c, d, e

final list = [ 1, 2, 3, 4, 5, 6];
list.forEach(print)

6. String Interpolation:

int x = 9;
int y = 6;

print('${x + y}'); // 15
print('${"flutter".toUpperCase()}'); // 'FLUTTER'
print('$x$y'); // 96

7. Functions:

// Named Function
  String fullName() {
    String firstName = "Barry";
    String lastName = "Allen";
    return '$firstName $lastName'; // 'Barry Allen'
  }

  int lengthOfText(String text) {
    return text.length; // returns length of text
  }

  int length = lengthOfText('200lab'); // 6

  // Arrow Syntak Function
  int sum(int a, int b) => a + b;

  // Optional named arguments
  int sumNumber(int a, int b, {int c = 0}) {
    return a + b + c;
  }
  print(sumNumber(1, 2, c: 3)); // 6

  // Lamda Function
  var list = [1, 4, 3, 2, 5];
  var odds = list.where((n) => n % 2 == 1).toList();
  print(odds); // [1, 3, 5]

  // High Order Function
  list.sort((a,b){
    return a > b ? 1 : -1;
  });
  print(list); // prints: [1, 2, 3, 4, 5]

8. Parsing:

var s1 = "456";
var s2 = "12.21";
var s3 = "18.01";
var s4 = "12.a56";

print(int.parse(s1)); // 456
print(double.parse(s2)); // 12.21
print(num.parse(s3)); // 12.21
print(num.parse(s4)); // error FormatException, null

9. Null-aware Operators:

int y; // initial null value
y ??= 10; // if y null, y will be 10

print(y ?? 08); // result: 08. Display the value on the left if it's not null else return the value on the right

10. Collection: List

// dynamic list
  var countryList = ['Vietnam', 'German', 'Poland'];
  print(countryList.length); // 3
  print(countryList[1]); // German
  countryList[2] = countryList[2].toUpperCase();
  print(countryList[2]); // POLAND

  countryList.insert(countryList.length, 'Thailand');
  print(countryList); // [Vietnam, German, POLAND, Thailand]
  print('${countryList.isEmpty}'); // false
  print('${countryList.last}'); // Thailand

  var fixedList = List<int>(2); // fixed list size

11. Collection: Set

var anotherSet = {1, 3, 5, 7};

  print('${anotherSet.contains(69)}'); // false

  anotherSet.add(9);
  print(anotherSet); // {1, 3, 5, 7, 9}

  anotherSet.remove(1);
  print(anotherSet); // {3, 5, 7, 9}

  anotherSet.addAll([11, 13]);
  print(anotherSet); // {3, 5, 7, 9, 11, 13}

  var declareSet = <int>{15, 17};
  anotherSet = anotherSet.union(declareSet);
  print(anotherSet); // {3, 5, 7, 9, 11, 13, 15, 17}

12. Collection: Map

// initial Map
  final student = {
    "id": 1,
    "name": "Barry Allen",
    "age": 23,
  };

  print(student); // {id: 1, name: Barry Allen, age: 23}

  // element access by key
  print(student['name']); // print: Barry Allen

  // access all keys
  student.keys.forEach(print); // prints: id, name, age

  // update value by key
  student.update("age", (value) => 18);

  print(student); // {id: 1, name: Barry Allen, age: 18}

  // Loop over key-value
  student.forEach((key, value) {
    print('$key - $value');
  }); /*
        id - 1
        name - Barry Allen
        age - 18
      */

13. Class:

class Cat {
    // field
    String name = 'Milo';

    // function
    void call(){
        print('Meow meow');
    }
}

14. Constructors:

class Location {
  // Properties
  double _lat;
  double _lng;

  // get value
  double get long => _lng;
  double get lat => _lat;

  // set value
  set latitude (double value) => _lat = value;
  set longitude (double value) => _lng = value;

  // constructor
  Location(this._lat,this._lng);

  // named constructor
  Location.withPosition(double lat,double lang){
    _lat = lat;
    _lng = lang;
  }
}

void main(){

  final location = Location(69.96,96.69);
  final location2 = Location.withPosition(12.23,23.21);

  location2.latitude = 11.0;
  location2.longitude = 12.21;

  print('new latitude: ${location2.lat}'); // 11.0
  print('new longitude: ${location2.long}'); // 12.21

}

15. Static members/ Methods:

class Channel{
    
    static String name = 'Channel name' ;

    static void changeChannelName(String name){
        print('New name: $name');
    }
}

16. Enum:

enum WeekDays { MON, TUES, WED, THURS, FRI, SAT,SUN, }

void main(){
  print(WeekDays.values); // [WeekDays.SUN, WeekDays.MON, WeekDays.TUES, WeekDays.WED, WeekDays.THURS, WeekDays.FRI, WeekDays.SAT]

  var today = WeekDays.SUN;

  switch(today){
    case WeekDays.MON:
    case WeekDays.TUES:
    case WeekDays.WED:
    case WeekDays.THURS:
    case WeekDays.FRI:
      print('Working day');
      break;
    case WeekDays.SAT:
    case WeekDays.SUN:
      print('Relaxing day');
      break;
  }
}

17. Inheritance:

class Person {
  String name;
  int age;

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

class Student extends Person{
    String id;
    Student({String id, String name, int age}) : super(name, age){
      this.id = id;
    }
}

void main() {
  final student1 = Student(id: "123",name: "Barry",age: 22);
  
  print('id: ${student1.id}');
  print('name: ${student1.name}');
  print('age: ${student1.age}');
  
}

18. Abstract / Interface:

class Person {
  String name;
  int age;
  int money = 0;

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

abstract class LenderBehavior {
  bool lendMoney(BorrowerBehavior borrower, int money);
  requestPayment();
}

abstract class BorrowerBehavior {
  void askForMoney(LenderBehavior lender, int money);
  void receiveMoney(LenderBehavior lender, money);
  int payMoneyBack();
}

class Lender extends Person implements LenderBehavior {
  BorrowerBehavior borrower;
  Lender(String name, int age) : super(name, age);

  @override
  bool lendMoney(BorrowerBehavior borrower, int money) {
    // if lender doesn't have enough money => false;
    if (this.money < money) return false;

    this.borrower = borrower;
    this.money -= money;

    // give money for borrower
    borrower.receiveMoney(this, money);

    return true;
  }

  @override
  requestPayment() {
    int returnMoney = borrower.payMoneyBack();

    if (returnMoney == null) {
      print("Borrower doesn't have enough money");
    } else {
      print("Yeah he is awesome guy");
      this.money += returnMoney;
      this.borrower = null;
    }
  }
}

class Borrower extends Person implements BorrowerBehavior {
  LenderBehavior lender;
  int debt = 0;

  Borrower(String name, int age) : super(name, age);

  @override
  void askForMoney(LenderBehavior lender, int money) {
    if (lender.lendMoney(this, money)) {
      print("what a hero");
    } else {
      print("I have to find someone else");
    }
  }

  @override
  int payMoneyBack() {
    int returnMoney;
    // if borrower has enough money for pay back to lender
    if (money >= debt) {
      money -= debt;
      returnMoney = debt;
      debt = 0;
      this.lender = null;
    } else {
      return null;
    }
    return returnMoney;
  }

  @override
  void receiveMoney(LenderBehavior lender, money) {
    this.lender = lender;
    debt = money;
    this.money += money;
  }
}

void main() {
  Lender lenderObj = new Lender("Barry", 22);
  lenderObj.money = 2000;
  Borrower borrowerObj = new Borrower("Duong", 18);

  // Example 1
  borrowerObj.askForMoney(lenderObj, 1000); // what a hero
  lenderObj.requestPayment(); // Yeah he is awesome guy

  // Example 2
  borrowerObj.askForMoney(lenderObj, 1000);
  borrowerObj.money = 800;
  lenderObj.requestPayment(); // Borrower doesn't have enough money
}

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